CA2218302A1

CA2218302A1 - Magnetic device, and process and apparatus for producing the same

Info

Publication number: CA2218302A1
Application number: CA 2218302
Authority: CA
Inventors: Shinji Furukawa; Nobuyoshi Yano; Floyd B. Humphrey
Original assignee: Unitika Ltd
Current assignee: Unitika Ltd
Priority date: 1996-10-15
Filing date: 1997-10-14
Publication date: 1998-04-15
Also published as: EP0837480A1

Abstract

A magnetic device comprising a soft magnetic thin film formed on a substrate, including a central area and a second area having a film thickness that is smaller than that of the central area, and wherein said magnetic device has a magnetic hysteresis loop which exhibits a discontinuous magnetization reversal. Also disclosed is a process and an apparatus for producing the magnetic device.

Description

MAGNETIC DEVICE, AND PROCESS AND
APPARATUS FOR PRODUCING THE SAME

FIELD OF THE INVENTION
This invention relates to a magnetic device which utilizes an abrupt change in magnetization that occurs in response to a change in an externally applied magnetic field.
The invention also relates to a process and an apparatus for producing the magnetic device.
BAC~GROUND OF THE INVENTION
The magnetization behavior of magnetic materials has been extensively utilized in various devices. Magnetic materials that are recently drawing the attention of researchers include those which, when the strength of a magnetic field exceeds a certain critical value, exhibit a sudden magnetic flux reversal as a discontinuous response.
If a pickup coil is placed in the neighborhood of such a magnetic material, a sharp voltage pulse is induced by the discontinuous magnetic flux reversal in the magnetic material. The resulting signal finds wide use in various magnetic devices for measuring magnetic fields (e.g., the earth's field), rotational speeds and flow rates.
Electronic article surveillance systems for preventing the theft of merchandise and article identification systems for enabling rapid delivery have recently gained in popularity. In addition to oscillation circuits, LC resonant circuits, magnetostrictive resonance materials and high permeability materials, magnetic materials which exhibit the above-described discontinuous magnetic flux reversal are used as identification markers. For example, Examined Japanese Patent Publication No. Hei-3-27958 (corresponding to U.S. Patents 4,660,025, 4,686,516 and 4,797,658) teaches a marker in the form of a filament of an Fe-based amorphous metal and a system using the marker.
The magnetization of the metal filament in a longitudinal direction is sufficiently stable so as not to readily undergo magnetic flux reversal, but the moment an externally applied magnetic field reaches a certain magnitude, a 180~ magnetic flux reversal occurs very abruptly. This property, which is also called a "large Barkhausen reversal", is utilized in the anti-theft systems described above. If an alternating magnetic field transmitted as an interrogating signal in the surveillance zone reaches a critical value, the metal filament undergoes a discontinuous magnetic flux reversal and an abrupt voltage pulse is induced in the detection coil. The waveform of the resulting pulse is subjected to frequency analysis and in accordance with the intensity or proportion of higher-order harmonic waves, the marker signal is used to determine whether an alarm should be sounded. This system is advantageous in that the marker is inexpensive and provides a highly discriminating performance.
In addition to the above-described amorphous metal filament, many other magnetic materials have been found to exhibit a discontinuous magnetization response. For example, Unexamined Published Japanese Patent Application No. Hei-1-150881 (corresponding to U.S. Patent 4,980,670) and No.
Hei-6-94841 (corresponding to U.S. Patent 5,313,192) teach materials obtained by annealing elongated amorphous metal ribbons in a magnetic field. According to Unexamined Published Japanese Patent Application No. Hei-4-218905 (corresponding to U.S. Patent 5,181,020), a thin film having a strong uniaxial magnetic anisotropy which is formed on a flexible polymeric substrate such as a resin film exhibits a discontinuous magnetic flux reversal and has good square hysteresis loop characteristics similar to the metal filament.
The thin film described in Unexamined Published Japanese Patent Application No. Hei-4-218905 (corresponding to U.S. Patent 5,181,020) produces an abrupt and discontinuous magnetization response similar to the amorphous metal filament if it is rendered in an elongated form measuring, for example, 1 mm wide by 50 mm long by 0.5 ~m thick along the axis that is easily magnetized (the magnetic easy axis). However, the magnetic characteristics of the thin film are highly sensitive to a demagnetizing field and have been found to deteriorate markedly when provided in a shorter, wider and thicker form. Although there is a strong need today for miniaturizing sensors and anti-theft markers, S it cannot be met by the above noted magnetic materials because they cannot provide an abrupt and discontinuous magnetization response unless provided in an elongated form.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the above problems of the prior art.
It is therefore an object of the present invention to provide a magnetic device which exhibits satisfactory magnetic characteristics despite its compact size. Another object of the invention is to provide a process for easily producing the magnetic device. A further object of the invention is to provide an apparatus for easily producing the magnetic device.
The above objects have been achieved, in a first embodiment of the present inventions, by providing a magnetic device comprising a soft magnetic thin film formed on a substrate, said soft magnetic thin film includes a central area and a second area having a film thickness that is smaller than that of the central area, and wherein said magnetic device has a magnetic hysteresis loop which exhibits a discontinuous magnetization reversal.

In a second embodiment of the present invention, the soft magnetic thin film of said second area has a film thickness gradient.
In a third embodiment, the present invention provides a process for producing the above-described magnetic device, which comprises:
positioning a mask member having an opening over said substrate with sufficient clearance so as not to contact the substrate, and depositing a magnetic thin film through the opening of said mask member and onto said substrate.
In a fourth embodiment, the present invention provides a process for producing the above-described magnetic device, which comprises:
winding a substrate on a cylindrical can, winding a mask member having an opening corresponding to the shape of said thin film onto said substrate via a spacer so as not to contact the substrate, and depositing a soft magnetic thin film through the opening of said mask member and onto said substrate.
In a fifth embodiment, the present invention provides a process for producing the above-described magnetic device, which comprises:
winding a substrate on a cylindrical can, positioning a mask member having an opening corresponding to the shape of said thin film over said substrate with sufficient clearance so as not to contact said substrate, and depositing a soft magnetic film through the opening of said mask member and onto said wound substrate.
In a sixth embodiment, the present invention provides an apparatus for producing the above-described magnetic device, which comprises:
means for superposing, in the followiny order, (1) a substrate, (2) a spacer and (3) a mask member having an opening corresponding to the shape of said thin film around a cylindrical can in such manner that the mask member does not contact the substrate,, means for depositing a soft magnetic thin film through the opening of said mask member and onto said .
substrate, and means for winding the superposed substrate, spacer and mask member.
In a seventh embodiment, the present invention provides an apparatus for producing the above-described magnetic device, means for winding a substrate or a cylindrical can, means for positioning a mask member having an opening corresponding to the shape of said thin film over said substrate with sufficient clearance so as not to contact said substrate, and means for depositing a soft magnetic film through the opening of said mask member and onto said wound substrate In an eighth embodiment, the present invention provides a process for producing a magnetic device comprising a thin film formed on a substrate, including a central area and a second area having a film thickness that is smaller than that of the central area, which comprises:
positioning a mask member between said substrate and a thin film deposition source, to thereby selectively block deposition from said deposition source, and depositing a thin film onto said substrate while moving said mask member and said substrate relative to each other, to thereby vary the area blocked by said mask member over time and form said second area having a reduced film thickness.
The magnetic device of the present invention has a discontinuous magnetization response characteristic which is not overly sensitive to the shape of the magnetic device.
Hence, the magnetic device of the invention exhibits satisfactory magnetic characteristics despite its compact size.

The process and apparatus of the present invention enable easy production of a compact magnetic device having a discontinuous magnetization response characteristic.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a simplified schematic diagram showing an example of the magnetic device of the present invention.
Fig. 2 is a simplified schematic diagram showing another example of the magnetic device of the present lnventlon .
Fig. 3 is a simplified schematic diagram showing yet another example of the magnetic device of the present invention.
Fig. 4 is a simplified schematic diagram showing an example of the apparatus for producing the magnetic device of the present invention.
Fig. 5 shows a partially enlarged view of the film forming zone of the apparatus of Fig. 4, and particularly the relative positions of a substrate, mask member and spacer provided therebetween.
Fig. 6 is a simplified schematic diagram illustrating the operating principle of the second production process of the present invention.
Fig. 7 is a simplified schematic diagram showing another example of the apparatus for producing the magnetic device of the present invention.

Fig. 8 is a simplified schematic diagram showing two different ways to cut out the magnetic device of the present invention from a substrate with a thin film produced with the apparatus of Fig. 7.
Fig. 9 is a simplified schematic diagram showing an example of thin film deposition with a mask member fixed on a substrate.
Fig. 10 is a simplified schematic diagram showing an example of thin film deposition with a rod of a mask member set on a substrate such that its longitudinal direction coincides with the direction of movement of the substrate.
Fig. 11 is a simplified schematic diagram showing an example of thin film deposition with a rod of a mask member set obliquely on a substrate such that its longitudinal direction forms a certain angle with the direction of movement of the substrate.
Fig. 12 is a simplified schematic diagram showing an example of thin film deposition with a sawtooth edged a mask member set on a substrate.
Fig. 13 is a diagram showing the hysteresis loop of the magnetic device manufactured in Example 1.
Fig. 14 is a diagram showing the hysteresis loop of the magnetic device manufactured in Comparative Example 1.
Fig. 15 is a graph showing the thickness gradient of the thin film formed in Example 2.

Fig. 16 is a diagram showing the hysteresis loop of the magnetic device manufactured in Example 2.
Fig. 17 is a diagram showing the hysteresis loop of the magnetic device manufactured in Comparative Example 2.
Fig. 18 is a diagram showing the hysteresis loop of the magnetic device manufactured in Example 3.
Fig. 19 is a diagram showing the hysteresis loop of the magnetic device manufactured in Example 4.
Fig. 20 is a diagram showing the hysteresis loop of the magnetic device manufactured in Comparative Example 3.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be described in further detail with reference to the accompanying drawings.
The magnetic devices according to the first and second embodiments of the present invention are described first.
The magnetic device of the present invention comprises a soft magnetic thin film formed on a substrate comprising an area having a smaller film thickness than the central area of the soft magnetic thin film. The soft magnetic thin film formed in that area desirably has a film thickness gradient.
Fig. 1 is a simplified schematic diagram showing an example of the magnetic device of the present invention.
Fig. l(a) is a plan view of the magnetic device and Fig. l(b) is a section A-A' of Fig. l(a). The magnetic device generally indicated by l in Fig. 1 is circular and an area 2 extending from position C to either end E has a smaller film thickness than the central area 3, and the film thickness of the area 2 progressively decreases toward either end.
Fig. 2 is a simplified schematic diagram showing another example of the magnetic device of the present invention. Similar to Fig. l, Fig. 2ta) is a plan view of the magnetic device, and Fig. 2(b) is a section A-A' of Fig.

2(a). The magnetic device generally indicated by 1 in Fig. 2 is rectangular, and an area 2 extending from position C to either end E has a smaller film thickness than the central area 3. Furthermore, the film thickness of the area 2 decreases progressively toward either end of the longer side.
Fig. 3 is a simplified schematic diagram showing yet another example of the magnetic device of the present invention. Similar to Fig. 1, Fig. 3(a) is a plan view of the magnetic device and Fig. 3(b) is a section A-A' of Fig.

3(a). The magnetic device generally indicated by 1 in Fig. 3 is rectangular and two areas 2 extending from position C to D
have a smaller film thickness than the central area 3.
Furthermore, the area between position D and either end E has the same film thickness as the central area.
With an area or areas thus formed being a smaller film thickness than the central area, the direction of magnetization of the magnetic device is reversed momentarily in a critical magnetic field, whereupon an abrupt magnetic pulse is radiated to the surroundings.
It should be noted that in the magnetic device of the invention, the soft magnetic thin film is present even in the area or areas which have a smaller film thickness than the central area. The magnetic device shown in Fig. 3 has a film thickness that is controlled to be smaller not at opposite ends but in areas slightly offset toward the center. If the film thickness of these areas is zero, the thin film is interrupted in the middle, such that the first object of the invention is not attained. On the other hand, the magnetic devices shown in Figs. 1 and 2 have a film thickness that is controlled to be smaller at opposite ends such that the film thickness decreases progressively toward either end until it becomes zero at the farthest end. These magnetic devices produce sufficiently abrupt magnetic pulses to attain the first object of the present invention.
In the case of controlling the film thickness at either end as shown in Figs. 1 and 2, the film thickness of the magnetic device preferably decreases progressively over a length of about 1 to 20 mm, more preferably 2 to 10 mm, and it becomes almost zero at the farthest end of the device.
The gradient of such a decrease in film thickness is desirably low.

In the case of controlling areas slightly offset from either end toward the center as shown in Fig. 3, the film thickness of the magnetic device preferably changes over a length of about 0.1 to 5 mm, more preferably 0.5 to 2 mm such that the smallest thickness ranges preferably from about 10%
to about 80% of the thickness in the central area. This range is more preferably from about 20% to about 70%, and most preferably about 30~ to about 65%.
The composition of the magnetic device of the present invention is selected in consideration of both the magnetic characteristics of the thin film per se and the characteristics required by the magnetic device. For example, the soft magnetic thin film either has uniaxial magnetic anisotropy or it may be isotropic. If the magnetic device is to be manufactured using an isotropic thin film, satisfactory device characteristics are easier to obtain with the circular shape shown in Fig. 1 than with the rectangular shapes shown in Figs. 2 and 3. On the other hand, if the magnetic device is to be manufactured using a thin film having uniaxial magnetic anisotropy, satisfactory device characteristics can be easily obtained even if the thin film is rectangular as shown in Figs. 2 and 3. In this case, the magnetic easy axis of the rectangular thin film may be aligned with the direction A-A' such that the areas with a controlled thin film cross the magnetic easy axis to cover the entire width of the magnetic device. Preferably, the magnetic easy axis forms an angle of no more than 20~, more preferably no more than 10~, with the lengthwise direction of the magnetic device. Most preferably, the two directions are S parallel to one another.
The areas of the magnetic device where the film thickness is controlled to be smaller than in the central area may be at either end of the device as shown in Fig. 2 or slightly offset therefrom toward the center as shown in Fig. 3. In the case of Fig. 3, the device characteristics thus obtained tend to be highly reproducible.
On the other hand, more abrupt magnetic pulses are sometimes obtained in the case of Fig. 2. Therefore, the areas of the magnetic device where the film thickness is controlled to be smaller than in the central area may be determined as appropriate depending on the intended application.
The general size of the magnetic device of the present invention is as follows. In the case of the circular ones, the diameter is generally within the range of from 8 mm to 70 mm, preferably 20 mm to 40 mm. In the case of the rectangular ones, the length of the shorter side is generally within the range of from 0.5 mm to 40 mm, preferably from 1 mm to 20 mm, and the length of the longer side is generally within the range of from 10 mm to 70 mm, preferably from 20 mm to 50 mm. Too short diameter of the circular magnetic device or too short length of the shorter side of the rectangular magnetic device is not preferable since the abrupt magnetization reversal would not be obtained or the intensity of the signal radiated to the surroundings by the magnetization reversal is not sufficient. On the other hand, too long diameter of the circular magnetic device or too long length of the shorter side of the rectangular magnetic device is not preferable since the abrupt magnetization reversal would not be obtained or the large device is not easy to handle. In addition, too short length of the longer side of the rectangular magnetic device is not preferable since the abrupt magnetization reversal would not be obtained, and too long length of the longer side of the rectangular magnetic device is not preferable since the large device is not easy to handle. In addition to the circular magnetic devices and rectangular magnetic devices described above, magnetic devices of other shapes have similar tendencies.
The operating mechanism of the magnetic device of the present invention is discussed below as follows. With respect to a magnetic material which experiences magnetic flux reversal as a result of the motion of magnetic domain walls, when the walls of reverse domains generated at either end of a sample of the magnetic material jump by moving very fast the moment the applied magnetic field reaches a critical value, abrupt magnetic pulses are radiated to the surroundings. On the other hand, the shorter and wider the shape of the sample, the greater the demagnetizing field that works on the sample. This makes the sample less likely to be magnetized but, at the same time, the discontinuous behavior of reverse domains is suppressed. Because of this effect, it has been extremely difficult to realize satisfactorily compact magnetic devices as discussed above.
In order to avoid the influence of the demagnetizing field, it would be effective to constrain the magnetic walls of reverse domains by a certain kind of force, and to have them jump by releasing the constraint the moment a magnetic field having a particular strength is reached. This force which constrains the magnetic walls is called a "pinning"
force, and in the present invention, the film thickness is controlled in selected areas to thereby provide an effect that is comparable to a pinning force. The coercivity of the thin film largely depends on its thickness and increases with an increasing film thickness. If the film thickness is reduced at either end, the coercivity of that area becomes greater than that of the other areas. As a result, the movement of the magnetic walls of the reverse domains present in that area is restricted such that they will move slowly as the strength of the external magnetic field increases. with the gradual increase in the external magnetic field, the tips of the reverse domains move inwardly. The moment they reach the central area beyond the areas having a controlled film thickness, the magnetic domain walls move fast enough to complete a magnetic flux reversal. This is because the central area has a smaller coercivity due to a sufficient film thickness. As a result of this rapid movement of the magnetic flux domains, abrupt magnetic pulses are radiated to the surroundings.
The above-described mechanism is realized in any of the magnetic devices shown in Figs. 1 to 3. It should also be noted that in magnetic devices which have a controlled film thickness at either end as in Figs. 1 and 2, an additional mechanism may come into play depending on the composition of the device to thereby generate magnetic pulses. For example, in a magnetic device having a geometry such that the film thickness decreases progressively toward either end, the magnetic field leakage will act on both ends.
This produces a local distribution of the demagnetizing field which is entirely different from what develops in a geometry having no changes in film thickness. Because of these effects, the domain structure at the farthest ends of the magnetic device becomes very stable and will not easily change. Ideally, such a magnetic device does not develop a closure domain structure, but develop a single domain at the farthest ends. Thus, upon the application of an external magnetic field, new reverse domains will nucleate. If the nucleating magnetic field is greater than the coercivity of the film, the magnetic domain walls will move very fast the moment the reverse domains have nucleated and magnetic pulses subsequently radiate.
Specific examples of the alloy composition of the soft magnetic thin film of the magnetic device of the present invention include crystalline materials such as NiFe, FeAlSi, FeAl and FeSi, fine crystalline Fe or Co alloy materials containing B, C, N, O, etc., and amorphous materials such as CoFeSiB, CoZrNb and FeC.
To form thin films of these materials, evaporation, plating and other commonly known techniques may be employed.
In the present invention, the use of a sputtering process is particularly preferred.
Depending on its composition, the magnetic device of the invention may desirably have uniaxial magnetic anisotropy. This property can be imparted by various methods such as the application of stress to the magnetic device, annealing in a uniaxial magnetic field, and annealing under an applied stress. An especially preferred sputtering method is described in Unexamined Published Japanese Patent Application No. Hei-4-218905 (corresponding to U.S. Patent 5,181,020), in which thin-film forming particles impinge on a substrate at an angle. According to this method, strong uniaxial magnetic anisotropy is readily induced in the sputtered film as such, to thereby produce a soft magnetic thin film having satisfactory magnetic characteristics.
Unexamined Published Japanese Patent Application No.
Hei-7-220971 (corresponding to EP-A-737,949) teaches another method of imparting uniaxial magnetic anisotropy. According to this published patent application, a magnetostrictive thin film is formed on a resin substrate having anisotropic thermal shrinkage under appropriate conditions. As a result, not only is uniaxial magnetic anisotropy induced in compliance with the anisotropic thermal shrinkage of the substrate, but a soft magnetic property is also ensured.
The magnetic device of the invention comprises a soft magnetic thin film formed on a substrate. The substrate is not limited to any particular type, and can be selected from common types such as glass, metals and resins. The use of a polyethylene terephthalate (PET) film is preferred since it is flexible and suited to large-scale production.
The magnetic device of the present invention has magnetic characteristics which exhibit an abrupt magnetic flux reversal in magnetic hysteresis, and it is characterized in that its discontinuous magnetization response characteristics are not so sensitive to the device shape. As already noted, conventional materials are highly affected by a demagnetizing field, and their characteristics have been found to abruptly deteriorate when fabricated in a wider and shorter form. However, the magnetic device of the present invention is less affected by the shape factor, and will effectively operate in sizes of one inch or less to produce a discontinuous abrupt magnetic flux reversal even if it is of a geometry having a high demagnetizing field coefficient.
Consequently, the present invention provides a very effective solution for meeting the need for smaller sensors and markers which is sure to become more pressing in the years to come.
Next, the process for producing the magnetic device of the present invention is described below. The production of the magnetic device of the present invention starts with preparing a thin film having a thickness difference in selected areas. This may be effectively accomplished by plasma or acid etching of a thin film which is exposed in only those areas where the film thickness needs to be controlled, but which is covered in other areas. However, it is more advantageous from the viewpoint of productivity and the like to cover a selected area of the substrate with a mask member during film formation so that the deposition of particles in that area is restricted to reduce the thickness of the film being formed in that area.
Thus, according to the first embodiment of the process for producing the magnetic device of the present invention, a mask member having a shape which restricts the inflow of particles deposited on a substrate is set with a sufficient clearance to prevent contact with the substrate, and wherein said clearance effectively controls the thickness gradient of the film that is formed.
It is a commonly adopted practice to form a patterned thin film on a substrate with a mask member placed in contact with the substrate in order to restrict the inflow of particles deposited on the substrate. However, according to this method, there is no film deposition under the mask member, whereas a film of the same thickness is deposited in those areas corresponding to the mask openings. Hence, cannot be used to produce a thin film for the magnetic device of the present invention which has a thickness difference in selected areas.
On the other hand, if a mask member having a desired shape in accordance with the size and characteristics of the magnetic device is set with a sufficient clearance to prevent contact with the substrate as a thin film is formed thereon, the vapourized film-forming particles will pass around behind the shade of the mask member. This results in a deposit on the corresponding areas of the substrate, to thereby form a thin film having a thickness gradient which gradually decreases in thickness. By cutting the substrate with the thus obtained thin film to a device shape such that it has a smaller film thickness in areas other than the central area, the magnetic device of the present invention can be produced which exhibits a discontinuous abrupt magnetic flux reversal.
In the present invention, the gradient of film thickness is chiefly controlled by the clearance (distance) between the substrate and the mask member. On the other hand, the amount of particles that pass around behind the shade of the mask member to deposit on corresponding areas of the substrate is largely influenced by the shape of the apparatus employed and its characteristics such as the mean free path and the plasma density which are determined by the operating pressure. Therefore, the distance between the substrate and the mask member cannot be specified by any unique value, except that a distance of about 0.1 to 5 mm is generally preferred.
If a thin film is formed with a flat substrate such as a glass plate that is successively fed into the film forming stage, a flat plate mask member can be superposed on the substrate with a spacer typically interposed therebetween to provide the necessary clearance from the substrate. Hence, the production process of the present invention is relatively easy to implement.
On the other hand, if a roll-to-roll apparatus is employed such that a highly flexible resin film is fed into the film forming stage as it is wound in a roll and a deposited film is then taken up, the mask member is not easy to set since the film is formed on the substrate which is wound around a cylindrical can. Therefore, the present invention also provides a process and an apparatus for efficiently producing the above-described magnetic device of the present invention using a roll-to-roll apparatus. The process and apparatus for attaining this aspect of the invention are described in detail below.
According to the first embodiment of the process of the present invention, a thin film is formed on a continuous substrate which is wound onto a cylindrical can in the roll-to-roll apparatus as follows. To produce the intended magnetic device by this process, a mask member of a given shape and having an opening of a given shape for restricting the inflow of particles deposited on the substrate is wound around the can superposed on the substrate with a spacer provided therebetween to prevent contact with the substrate.
The thin film is formed on the substrate as the substrate, the spacer and the mask member are taken up.
The mask member for use in the present invention may be selected from among metal (e.g. stainless steel~ folls, glass cloths, resin films, etc. The mask member is wrapped around the cylindrical can with the interposed spacer to provide sufficient clearance from the substrate and, hence, may occasionally fail to be thoroughly cooled with the can.
If, on account of this insufficient cooling, the mask member is heated during deposition by sputtering, evaporation and the like methods, the mask member is preferably made of a heat-resistant material such as glass, metal or a polyimide.
An example of the spacer for use in the present invention is a beam-like element consisting of a plurality of metal wires running parallel to each other. Metal wires such as copper wires are preferred as the spacer because the distance from the substrate can be controlled by the wire diameter and because the metal wires have a high heat resistance. As discussed above, the preferred range of the wire diameter is not uniquely determined since it depends on the apparatus used to produce the magnetic device of the invention. Generally speaking, the range of the wire diameter is from about 0.5 to about 5 mm.
Fig. 4 is a simplified schematic diagram showing an example of the roll-to-roll apparatus for producing the magnetic device of the present invention. Fig. 5 shows a partially enlarged film forming zone of the apparatus of Fig.

4, particularly the relative positions of the substrate 4, mask member lO and spacer 9 provided therebetween.
As shown in Fig. 5, the mask member 10 has a circular opening 13 because the magnetic device to be produced is of the circular type shown in Fig. 1; however, the present invention is not so limited, and an opening of a desired shape may be provided in the mask member 10.

Because vapourized film-forming particles will pass around behind the mask member and deposit in corresponding areas of the substrate, the area where the particles are deposited to form a thin film accordingly becomes larger than the opening in the mask member. Considering this fact, the opening provided in the mask member may be rendered somewhat smaller than the magnetic device that is to be finally produced. As an example, a circular opening having a size of about 15 to 22 mm will suffice if a magnetic device with a diameter of 25 mm is required.
In Fig. 5, only one opening is provided in the mask member but this is just for the sake of convenience in explanation. In order to realize mass production of magnetic devices, a plurality of openings are preferably arranged side by side so that many magnetic devices can be simultaneously manufactured in one step. In this case, utmost care must be exercised in determining the distance between openings provided in the mask member. As discussed above, due to the clearance between the mask member and the substrate, a thin film will be deposited considerably outward from the opening in the mask member. If the distance between openings is unduly small, the individual devices will overlap.
Therefore, the distance between openings formed in the mask is preferably as large as possible, and are generally spaced by at least 10 mm, possibly at least 15 mm. As an example, if magnetic devices having a diameter of 25 mm are to be manufactured on a film substrate having a width of 1 m, about 20 to 30 openings can be provided per 1 m of the mask member in both horizontal and vertical directions. Hence, about 400 to 900 magnetic devices can be manufactured simultaneously per square meter of the mask member.
As shown in Figs. 4 and 5, metal wires as spacers 9 are placed on top of the substrate 4 and the mask member 10 having a circular opening 13 is placed on the spacers 9 such that the substrate 4, the spacers 9 and the mask member 10 are wound around a can 11 in superposition on each other.
Thin-film forming particles 14 pass through the circular opening 13 to deposit on the substrate 4. Because the spacers 9 provide a certain clearance between the substrate 4 and the mask member 10, the particles 14 will pass around behind the mask member in an area near the circular opening 13 to deposit in a corresponding area of the substrate 4. As a result, a thin film is deposited on the substrate 4 to a larger extent than the diameter of the circular opening 13, and the area of the deposited thin film which is near the circumference decreases in film thickness towards the peripheral edge thereof.
The apparatus for producing magnetic devices by the above method has both means for winding the substrate, the spacer and the mask around the can in superposition, and means for taking up the overlapping substrate, spacer and mask member. In order to wind the respective materials for the substrate, spacer and mask member around the can in superposition and to take them up after a thin film has been formed, a roll of the respective superposed materials may be fed into the film coater unit. In the film coater unit, the superposed materials are wound onto the can, and the substrate is taken up together with the deposited film.
Alternatively, the respective materials may be separately fed into the film coater unit such that they are superposed on the can 11 and, after a thin film has been formed, the respective materials are separately taken up (this is the method illustrated in Fig. 4).
Referring to Fig. 4, the substrate 4, the spacer 9 and the mask member 10 are supplied by associated feed rolls 8 and guide rolls 7, and are superposed on each other on the peripheral surface of the can 11. As the can 11 rotates in the direction of the arrow shown in Fig. 4, the superposed materials are fed onto a deposition source 12, where a thin film is deposited on the substrate. Thereafter, the substrate with the deposited film, the spacer and the mask member pass on associated guide rolls 6 and are wound up by associated take-up rolls S.
Thus, the mask member is supplied in a continuous form such as a film or a foil and onto a deposition source simultaneously with the substrate on which a thin film is being formed. This method provides great latitude in selecting the shape of the magnetic device depending upon the shape of the opening in the mask member and, hence, is suitable for producing circular magnetic devices. In addition, the clearance between the mask member and the substrate can be held constant, and this is very effective for controlling the film thickness.
If rectangular magnetic devices of the types shown in Figs. 2 and 3 are to be produced by a roll-to-roll apparatus, a more simplified process and apparatus can be employed. The process and the apparatus of this second embodiment are described below.
The simplified process for producing the magnetic device of the invention with a roll-to-roll apparatus is realized. A thin film is formed on a substrate as it is wound onto a cylindrical can. A mask of a given shape for restricting the inflow of particles deposited on the substrate is set below the can with a sufficient clearance to prevent contact with the substrate, and where the thin film is formed as the substrate is taken up.
Fig. 6 is a simplified schematic diagram illustrating the operating principle of this production process. A thin film is deposited on the substrate 4 using deposition source 12 such as a sputtering cathode. As shown, a mask member 10 is placed in a selected area below the can, preferably just underneath it, with sufficient clearance to prevent contact with the substrate 4. In those areas of the substrate 4 which are not covered with the mask member 10, vapourized film-forming particles 14 travel directly to the substrate 4, thereby forming a thin film (having a greater thickness as indicted by 15), whereas in the area of the substrate which is just above the mask member 10, the particles 14 are blocked by the mask member 10 and fail to form a thin film.
However, in the neighborhood of either end of the mask member 10, the particles 14 pass around behind the mask and are deposited in the corresponding areas of the substrate, to form a thin film (having a smaller thickness as indicated by 2) which progressively decreases in thickness. This effect is utilized by the subject production method of the invention.
Fig. 7 is a simplified schematic diagram showing an example of a (roll-to-roll) apparatus for producing the magnetic device of the invention by the method described above. In Fig. 7, the substrate 4 is wound onto can 11 after passing on guide roll 7, and a thin film is deposited on the substrate 4 by deposition source 12. In the apparatus shown in Fig. 7, a plurality of linear mask members 10 (four mask members are shown in Fig. 7) are set just beneath the can 11 such that they do not contact the substrate 4, and films having a smaller thickness 2 similar to the one shown in Fig.
6 are formed in those areas of the substrate which correspond to the shades of the mask members 10. The substrate having the thin film formed thereon is sent to a take-up roll via guide roll 6. The thin film on the substrate 4 wound up by the take-up roll consists of alternating bands of the thicker portion 15 and the thinner portion 2, and the magnetic device of the invention is cut out from the substrate 4.
Fig. 8 is a simplified schematic diagram showing two deferent ways to cut out the magnetic device of the present invention from the substrate with the thin film that was manufactured with the apparatus of Fig. 7. As described above, the thin film formed on the substrate 4 consists of alternating bands of the thicker portion 15 and the thinner portion 2. If a magnetic device of the shape indicated by 16 is cut out from this substrate, the device 1 has a thin film of the smaller thickness 2 at each of the farthest ends as shown in Fig. 8(a) and this is the magnetic device shown in Fig. 2. If, on the other hand, a magnetic device of the shape indicated by 17 is cut out from the substrate, the device 1 has a thin film having a smaller thickness in areas slightly offset toward the center as shown in Fig. 8(b) and this is the magnetic device shown in Fig. 3.
As seen from Fig. 8, the width of the mask member 10 determines the shape of the areas 2 of the thin film having a controlled thickness, and it ranges preferably from 0.1 to 30 mm, with the range of 0.5 to 10 mm being more preferred. If the width of the mask member 10 is less than 0.1 mm, it is too narrow to provide the intended film thickness gradient.
On the other hand, if the width of the mask member 10 exceeds 30 mm, the overall size of the magnetic device increases to the extent that a compact magnetic device is not realized which is a primary objective of the invention.
As described above, the distance between the mask member 10 and the substrate 4 cannot be uniquely determined because it varies with the characteristics of the specific film coater unit that is employed. However, in most cases, a range of from about 0.1 to about 5 mm is preferred.
The mask member 10 may be rectangular or in the form of a round bar. Alternatively, it may assume any cross-sectional shape such as a triangle or an ellipse. A suitable shape may be selected as appropriate in consideration of the gradient of the film thickness of the magnetic device or the shape of the areas of the thin film which are to have a controlled thickness. Fig. 7 shows the case of using linear masks. Because the surface of the can is curved, the clearance between the mask member and the can increases progressively with increasing distance from the center line of the can and this may occasionally deteriorate the film thickness control. If this possibility exists, it is effective to install a protector to ensure that a thin film is formed only in the neighborhood of the central position of the can.
Forming a mask member having the same curvature as the can is a very effective means because it permits the clearance between the mask member and the substrate to be -held constant.
In addition to the first process described above, the magnetic device of the invention can also be produced by a second process which is described below.
In this second process, the magnetic device comprising a substrate and a thin film formed thereon including a central area and an area having a film thickness that is smaller than that of the central area is preferably produced by either evaporation or sputtering. In order to prepare this thin film on the substrate, a mask member for selectively blocking the deposition of a thin film is used.
The second process for producing the magnetic device of the invention is characterized in that the mask member for selective blocking of the deposition of the thin film LS
provided between the substrate and an evaporation source or a sputtering cathode. In this case, either the substrate or the mask member is moved such that the region of the substrate which is shaded by the mask member varies over time.

Consider the case shown in Fig. 9, where masks 19 are fixed on a stationary substrate 18 and particles are deposited on the substrate to form a thin film. No film is deposited at all in the areas of the substrate which are beneath the mask members 19. However, in the open areas which are not covered with the mask members 19, a film of uniform thickness is deposited on the substrate 18. As a result, the deposited thin film is interrupted at areas 20 where no film is formed, and the film has a discontinuous thickness profile in which the thickness of the film changes discontinuously from one region to another. Hence, this method is not capable of producing a thin film having a thickness gradient that is needed for the magnetic device of the invention which should exhibit an abrupt magnetic flux reversal when the strength of an external magnetic field reaches a critical value.
If a thin film is formed by moving either of the substrate or the mask member, the thickness of the thin film thus formed is affected by the relative positions of the mask member and the substrate. Consider the case shown in Fig.
10, where rods of mask member 19 are set such that their lengthwise direction is aligned with the direction of movement of the substrate 18. The substrate travels in the direction shown by the arrow in Fig. 10. Even if the mask member 19 or the substrate 18 move relative to each other, a given point on the substrate 18 is at all times in a position such that it is shaded or not shaded by the mask members 19.
In this case, the film formed on the substrate 19 is of the same type as shown in Fig. 9 and no thin film will form that has the desired thickness gradient.
However, if, as in the present invention, the substrate or the mask member is moved such that the region of the substrate which is shaded by the mask member varies with time, a film is obtained which has an area of continuously ranging thickness. Even if the mask member 19 consists of rods as shown in Fig. 10, they may be set obliquely as shown in Fig. 11 such that their lengthwise axes form an angle with the direction of movement of the substrate 18. The substrate travels in the direction shown by the arrow in Fig. 11. If this requirement is met, the region of the substrate which is shaded by the mask member 19 varies with time and the thickness of the film thus formed can be adjusted by the length of time over which the substrate 18 is covered by the mask member 19. As a result, the thin film is provided with areas 2 having the desired thickness gradient. The extent of the areas 2 is determined by the angle that the lengthwise axis of the mask member 19 forms with the direction of movement of either the substrate 18 or the mask member 19.
The film thickness gradient can be adjusted more precisely by using a nonlinear mask member, for example, one having a sawtooth edge as indicated by 19 in Fig. 12. The substrate travels in the direction shown by the arrow in Fig.
12. If the substrate 18 or the mask member 19 having such a nonlinear shape is moved, the length of time over which the substrate is covered by the shade of the sawtooth edge 21 varies continuously, to thereby form areas 2 having a film thickness gradient. In this case, the lengthwise axis of the mask member l9 may be in complete alignment with the direction of movement of the substrate 18 or the mask member 19.
The foregoing description has been directed to a method of forming a thin film on a substrate that is held in a flat state. Flexible substrates such as resin films or metal foils can be processed by the roll-to-roll method in which a roll of the substrate is unwound and passed around a cylindrical can so that a thin film is continuously formed on the substrate as it is wound by a take-up roll, and the invention is also effective for this method. In this case, the mask member is set below the can around which the substrate has been wound. In order to achieve more precise adjustment of the film thickness, it is more effective to bend the mask member in conformance with the curvature of the can so that the mask member maintains a constant clearance from the substrate.

The following Examples and comparative Examples are provided for the purpose of further illustrating the present invention. However, the present invention should not be construed as being limited thereto.
Example 1 A fluororesin impregnated glass cloth 75 ~m thick (product of Yodogawa Kasei Co., Ltd.) was punched to form circular holes (15 mm~) at intervals of 30 mm, and the thus prepared sheet was used as a mask member. A roll-to-roll apparatus was used in the coating process. A PET
(polyethylene terephthalate) film 100 ~m thick was wrapped as a substrate onto a water-cooled can, and copper wires 0.9 mm in diameter were placed as spacers on top of the substrate.
The separately prepared mask member was superposed on the copper wires. Thus, the mask member was set on the substrate with a clearance of about 0.9 mm provided therebetween.
Using a DC magnetron sputtering apparatus of the type described in Unexamined Published Japanese Patent Application No. Hei-4-218905 (corresponding to U.S. Patent 5,181,020), in which magnets are positioned below a target and the magnetic flux from the magnets is guided by yokes to generate a high-density plasma on the target surface, an amorphous thin film having the composition Co5lFe26SilOBl3 (the subscripts represent atomic %) was formed in a thickness of 0.5 ~m on the substrate, which was taken up continuously together with the spacers and the mask member. The substrate with the thin film formed thereon was cut out in a specified geometry to manufacture magnetic device samples of the invention. Each sample was circular with a diameter of about 25 mm, and in the area extending over the range of 7.5 to 12.5 mm from the center of the circle, the film thickness decreased continuously to provide a thickness gradient.
The magnetic characteristics of each sample were measured with an ac B-H tracer (AC, BH-lOOK of Riken Denshi Co., Ltd.) at 60 Hz. Since each sample exhibited uniaxial magnetic anisotropy, the measurement was conducted with a pickup coil set in the center of the sample in the direction of the magnetic easy axis. The result is shown in Fig. 13.
As seen in Fig. 13, in each sample of the invention, the magnetic device had a satisfactory square hysteresis loop and the magnetization changed abruptly at -1 Oe and +0.6 Oe to provide discontinuous jumps in magnetization.
Comparative Example 1 An amorphous thin film having the composition Co5lFe26SilOB13 (the subscripts represent atomic %) was formed on a PET (polyethylene terephthalate) film using the same apparatus and under the same conditions as in Example 1, except that no spacer copper wires were not interposed between the substrate and the mask member (i.e., the substrate was in contact with the mask member). Circular thin films were formed each having a diameter of 15 mm equal to the diameter of the openings in the mask member. These thin films had a substantially uniform thickness. Magnetic device samples were cut out from the circular thin films and their magnetic characteristics were measured using the same method as in Example l. The result is shown in Fig. 14. As seen from Fig. 14, the magnetic device samples made of the thin films having a uniform thickness did not produce the desired square hysteresis loop under the influence of a strong demagnetizing field. In addition, the change in magnetization was continuous, and no discontinuous jumps in magnetization were observed.
Example 2 A 100-~m thick PET (polyethylene terephthalate) film was set as a substrate on a roll-to-roll apparatus of the same type as used in Example 1. Two stainless steel bars each having a diameter of 4 mm were spaced apart by 20 mm and set as masks just beneath the can, with the smallest clearance from the substrate adjusted to 0.1 mm.
Then, by continuously taking up the substrate, an amorphous thin film having the composition Co5lFe26SilOBl3 (the subscripts represent atomic %) was formed in a thickness of 0.5 ~m on the substrate using a DC magnetron sputtering apparatus of the same type as used in Example l. Two bands of a film having a smaller thickness were observed on the substrate at a spacing of about 20 mm in the direction of travel of the substrate, and the change in the film thickness was continuous.
The thickness profile of the thin film was evaluated by the following procedure. A water-soluble ink was preliminarily printed in a pattern of 1 mm x 50 mm on the substrate PET film. The length of the ink pattern and that of the mask were oriented in a vertical direction. After film formation, the water-soluble ink and the overlying thin film were washed away with water. Thus, a level difference was established between the area retaining the thin film and the area from which it was removed, and the difference was measured with a surface profile measuring system Dektak 300 of Dektak Co., Ltd. As a result, the film thickness was found to be 0.6 ~m in the central area between the traces of the two masks (which corresponded to the central area of the magnetic device). The thickness profile in the neighborhood of each mask was measured by scanning at 0.5-mm intervals.
The result is shown in Fig. 15. As seen from Fig. 15, the thickness of the thin film deposited on the substrate varied continuously on account of the masks, and the thickness was smallest at an area corresponding to the center of either mask (about 63% of the thickness at the areas not covered by the mask). Thus, by providing the above masking structure, areas having a smaller thickness than at the center of the magnetic device were formed, and the film thickness continuously varied to provide a gradient.
For the measurement of magnetic characteristics, a PET film not having a printed pattern of a water-soluble ink S was used as a substrate, and a thin film was formed thereon under the same conditions described above. From the substrate having the thin film formed thereon, rectangular samples measuring about 28 mm long by 10 mm wide were cut out such that the area having the smaller thickness would occur at either, to thereby obtain magnetic device samples of the invention.
The magnetic characteristics of these samples were measured by the same method as employed in Example 1. Since each magnetic device sample exhibited uniaxial magnetic anisotropy in the longitudinal direction, the measurements were conducted along the magnetic easy axis. The result is shown in Fig. 16. As seen from Fig. 16, the magnetic device samples of the invention each had a satisfactory square hysteresis loop, and the magnetization changed abruptly at -1 Oe and +1.1 Oe to provide discontinuous jumps in magnetization.
Comparative Example 2 An amorphous thin film having the composition Co5~Fe26Sil0B13 (the subscripts represent atomic %) was formed on a PET film using the same apparatus and under the same conditions as in Example 2, except that a mask member was not set below the can. As a result, a thin film was uniformly deposited on the substrate with no thickness gradient. From this substrate, rectangular samples measuring 28 mm long by 10 mm wide as in Example 2 were cut out such that the length of each sample was oriented parallel to the width of the substrate. The magnetic characteristics of the cut out samples were measured by the same method as used in Example 2. The result is shown in Fig. 17. As seen from Fig. 17, the magnetic device samples made of thin films having a uniform thickness did not produce the desired square hysteresis loop, but rather produced a largely skewed loop under the influence of a strong demagnetizing field. In addition, the change in magnetization was continuous, and discontinuous jumps in magnetization were not obtained.
Example 3 From the substrate prepared in Example 2, rectangular magnetic device samples measuring about 38 mm long by 10 mm wide were cut out such that areas having a smaller thickness were located 5 mm from either end. The magnetic characteristics of these samples were measured by the same method as used in Example 1. Since each magnetic device sample exhibited uniaxial magnetic anisotropy in the longitudinal direction, the measurements were conducted along the magnetic easy axis. The result is shown in Fig. 18. As seen from Fig. 18, the magnetic device samples of the invention each had a satisfactory square hysteresis loop, and the magnetization changed abruptly at +0.4 Oe to provide discontinuous jumps in magnetization.
Example 4 A 100-~m thick polyethylene terephthalate (PET) film was set as a substrate on a roll-to-roll apparatus, and stainless steel sheets measuring 10 mm wide by 30 cm long which were bent to the curvature of the can were set as mask members just beneath the can. The two stainless steel sheets as mask members were spaced apart by 20 mm. The lengthwise direction of each mask member formed an angle of 5~ with the direction of travel of the substrate.
By continuously taking up the substrate on the setup described above, an amorphous thin metallic film having the composition Co5lFe26Sil0Bl3 (the subscripts represent atomic %) was formed in a thickness of 0.5 ~m on the substrate using a DC magnetron sputtering apparatus. Two bands of a film having a smaller thickness were observed on the substrate at a spacing of about 17 mm in the direction of travel of the substrate, and the change in film thickness was continuous.
From the thus prepared substrate, rectangular samples measuring 25 mm long on the longer side (across the width of the substrate) by 10 mm wide were cut out such that the area having the smaller thickness was located at either end. The cut-out samples were magnetic devices. The magnetic characteristics of these devices were measured with an ac B-H
tracer (AC, BH-100 K of Riken Denshi Co., Ltd.) at 60 Hz.
The result is shown in Fig. 19.
As seen from Fig. 19, the magnetic device samples manufactured by the process of the invention had a satisfactory square hysteresis loop, and the magnetization changed abruptly at -0.7 Oe and +0.9 Oe to provide discontinuous jumps in magnetization.
Comparative Example 3 An amorphous metallic thin film having the composition Co5lFez6Sil0Bl3 (the subscripts represent atomic %) was formed on a polyethylene terephthalate (PET) film using the same apparatus and under the same conditions as in Example 4, except that the length of the mask members was adjusted parallel to the direction of travel of the substrate (i.e., the angle between the lengthwise direction of the mask members and the direction of travel of the substrate was zero degrees). Because of this parallel alignment, the region of the substrate which was shaded by the mask members did not vary with time. The substrate having a thin film thus formed thereon was characterized as having two bands of film-free areas that were spaced apart by about 20 mm in the direction of travel of the substrate, and the change in film thickness at the boundary was clearly visible.

From the thus prepared substrate, rectangular samples measuring 25 mm long on the longer side (across the width of the substrate) by 10 mm wide were cut out such that a film-free area was located at either end. The cut-out samples were magnetic devices. The magnetic characteristics of these devices were measured as in Example 1, and the result is shown in Fig. 20.
As seen from Fig. 20, the magnetic device samples manufactured without varying over time the region of the substrate shaded by the mask members had hysteresis characteristics exhibiting a lower degree of squareness as compared to the samples of Fig. 19.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims

1. A magnetic device comprising a soft magnetic thin film formed on a substrate, including a central area and a second area having a film thickness that is smaller than that of the central area, and wherein said magnetic device has a magnetic hysteresis loop which exhibits a discontinuous magnetization reversal.

2. The magnetic device as claimed in claim 1, wherein the soft magnetic thin film of said second area has a film thickness gradient.

3. The magnetic device as claimed in claim 1, wherein the film thickness in areas other than said central area is smaller than that of said central area.

4. The magnetic device as claimed in claim 1 having a circular shape, and including a central area of uniform film thickness and a peripheral area having a film thickness that is smaller than that of the central area and which progressively decreases toward the periphery of the magnetic device.

5. The magnetic device as claimed in claim 4, wherein the film thickness at said peripheral area progressively decreases over a distance of about 1 to 20 mm and becomes almost zero at the periphery.

6. The magnetic device as claimed in claim 1 having a rectangular shape, and including a central area of uniform film thickness and an area at opposite ends thereof having a film thickness that is smaller than that of the central area and which progressively decreases toward an edge of the device.

7. The magnetic device as claimed in claim 6, wherein the film thickness at said opposite ends progressively decreases over a distance of about 1 to 20 mm and becomes almost zero at the edge.

8. The magnetic device as claimed in claim 1 having a rectangular shape, and including a central area of uniform thickness and an area offset from an end thereof having a film thickness that is smaller than that of the central area.

9. The magnetic device as claimed in claim 8, having an area at an end of said magnetic device having a film thickness that is the same as that of the central area.

10. The magnetic device as claimed in claim 8, wherein the film thickness at the offset area changes over a length of about 0.1 to 5 mm such that the smallest thickness of said offset area ranges from about 10% to about 80% that of the central area.

11. A process for producing a magnetic device comprising a soft magnetic thin film formed on a substrate, including a central area and a second area having a film thickness that is smaller than that of the central area, and wherein said magnetic device has a magnetic hysteresis loop which exhibits a discontinuous magnetization reversal, comprising the steps of:
positioning a mask member having an opening over said substrate with sufficient clearance so as not to contact the substrate, and depositing a soft magnetic thin film through the opening of said mask member and onto said substrate.

12. The process as claimed in claim 11, wherein the soft magnetic thin film of said second area has a film thickness gradient, and which process further comprises the step of controlling the film thickness gradient by adjusting the distance between the mask member and the substrate.

13. The process as claimed in claim 11, wherein the distance between the mask member and the substrate is about 0.1 to 5 mm.

14. A process for producing a magnetic device comprising a soft magnetic thin film of a given shape formed on a substrate, including a central area and a second area having a film thickness that is smaller than that of the central area, and wherein said magnetic device has a magnetic hysteresis loop which exhibits a discontinuous magnetization reversal, comprising the steps of:
winding a substrate on a cylindrical can, winding a mask member having an opening corresponding to the shape of said thin film onto said substrate via a spacer so as not to contact the substrate, and depositing a soft magnetic film through the opening of said mask member and onto said substrate.

15. The process as claimed in claim 14, wherein said spacer comprises a plurality of metal wires having a diameter of about 0.5 to about 5 mm.

16. A process for producing a magnetic device comprising a soft magnetic thin film of a given shape formed on a substrate, including a central area and a second area having a film thickness that is smaller than that of the central area, and wherein said magnetic device has a magnetic hysteresis loop which exhibits a discontinuous magnetization reversal, comprising the steps of:
winding a substrate on a cylindrical can, positioning a mask member having an opening corresponding to the shape of said thin film over said substrate with sufficient clearance so as not to contact said substrate, and depositing a soft magnetic film through the opening of said mask member and onto said wound substrate.

17. An apparatus for producing a magnetic device comprising a soft magnetic thin film of a given shape formed on a substrate, including a central area and a second area having a film thickness that is smaller than that of the central area, and wherein said magnetic device has a magnetic hysteresis loop which exhibits a discontinuous magnetization reversal, which comprises:
means for superposing, in the following order, (1) a substrate, (2) a spacer and (3) a mask member having an opening corresponding to the shape of said thin film around a cylindrical can in such manner that the mask member does not contact the substrate, means for depositing a soft magnetic thin film through the opening of said mask member and onto said substrate, and means for winding the superposed substrate, spacer and mask member.

18. An apparatus for producing a magnetic device comprising a soft magnetic thin film of a given shape formed on a wound substrate, including a central area and a second area having a film thickness that is smaller than that of the central area, and wherein said magnetic device has a magnetic hysteresis loop which exhibits a discontinuous magnetization reversal, which comprises:
means for winding a substrate on a cylindrical can, means for positioning a mask member having an opening corresponding to the shape of said thin film over said substrate with sufficient clearance so as not to contact said substrate, and means for depositing a soft magnetic film through the opening of said mask member and onto said wound substrate.

19. A process for producing a magnetic device comprising a thin film formed on a substrate, including a central area and a second area having a film thickness that is smaller than that of the central area, comprising the steps of:
positioning a mask member between said substrate and a thin film deposition source, to thereby selectively block deposition from said deposition source, and depositing a thin film onto said substrate while moving said mask member and said substrate relative to each other, to thereby, vary the area blocked by said mask member over time and form said second area having a reduced film thickness.

20. The process as claimed in claim 19, wherein said thin film deposition source comprises an evaporation source or a sputtering cathode.

21. The process as claimed in claim 19, wherein said mask member comprises a plurality of rods having a lengthwise axis, and which process comprises positioning the lengthwise axes of said rods at an angle relative to the direction of movement of said substrate.

22. The process as claimed in claim 19, wherein said mask member has a nonlinear shape.