Classifications

• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2405—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting characterised by the tag technology used
  • G08B13/2408—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting characterised by the tag technology used using ferromagnetic tags
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/04—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering with simultaneous application of supersonic waves, magnetic or electric fields
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/007—Heat treatment of ferrous alloys containing Co
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2405—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting characterised by the tag technology used
  • G08B13/2408—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting characterised by the tag technology used using ferromagnetic tags
  • G08B13/2411—Tag deactivation
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2428—Tag details
  • G08B13/2437—Tag layered structure, processes for making layered tags
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2428—Tag details
  • G08B13/2437—Tag layered structure, processes for making layered tags
  • G08B13/244—Tag manufacturing, e.g. continuous manufacturing processes
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2428—Tag details
  • G08B13/2437—Tag layered structure, processes for making layered tags
  • G08B13/2442—Tag materials and material properties thereof, e.g. magnetic material details
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
  • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
  • H01F1/147—Alloys characterised by their composition
  • H01F1/153—Amorphous metallic alloys, e.g. glassy metals
  • H01F1/15308—Amorphous metallic alloys, e.g. glassy metals based on Fe/Ni
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
  • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
  • H01F1/147—Alloys characterised by their composition
  • H01F1/153—Amorphous metallic alloys, e.g. glassy metals
  • H01F1/15341—Preparation processes therefor
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/0206—Manufacturing of magnetic cores by mechanical means
  • H01F41/0213—Manufacturing of magnetic circuits made from strip(s) or ribbon(s)
  • H01F41/0226—Manufacturing of magnetic circuits made from strip(s) or ribbon(s) from amorphous ribbons
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F13/00—Apparatus or processes for magnetising or demagnetising
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/42—Piezoelectric device making
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49002—Electrical device making
  • Y10T29/4902—Electromagnet, transformer or inductor

Definitions

• the present invention relates to magnetic amo ⁇ hous alloys and to a method
• the present invention is also directed
• the present invention furthermore is directed to a
• magnetomechanical electronic article surveillance system employing such a marker
• amo ⁇ hous magnetostrictive alloy as well as to a method for making the amo ⁇ hous magnetostrictive alloy and a
• alloy strips in a magnetic field of 4 kOe which was oriented across the ribbon width, i.e. pe ⁇ endicular to the ribbon axis and in the ribbon plane.
• Amo ⁇ hous metals can be prepared in the
• Alloys for practical use are basically composed of Fe, Co and /or Ni
• J s is the saturation magnetization
• the applied field before reaching saturation can be varied from values well below
• transformer cores for example (cf. Herzer et al,
• amorphous metals provides a useful means to achieve control of the vibrational
• bias magnet magnetized ferromagnetic strip
• the marker at the resonance frequency provides the marker with signal identity.
• This signal identity can be removed by changing the resonant frequency by means of the applied field.
• the marker can, for example, be deactivated by degaussing the bias magnet, which removes the applied magnetic field, and thus changes the resonant frequency appreciably.
• Such systems originally cf. European Application 0 093 281, and Application PCT WO 90/03652 used markers made of amo ⁇ hous
• article surveillance systems removes a number of deficiencies associated with the markers of the prior art which use as prepared amorphous material.
• the markers of the prior art which use as prepared amorphous material.
• ribbon width i.e. the magnetic field direction was oriented perpendicular to the ribbon
• Such transverse field-annealing can be performed, for example, batch ⁇
• annealing can be performed in a continuous mode by transporting the alloy ribbon
• the uniaxial anisotropy can also be caused by mechanisms other
• a typical situation is, for example, that the anisotropy is
• the visible domains are generally closure domains while
• Gyorgy states that the domain structure of the pe ⁇ endicularly
• annealed sample is typical for a uniaxial material with the easy axis normal to the
• closure domain stripes are oriented parallel to the applied
• transverse field-annealing seems to be cleariy advantageous if a linear hysteresis loop and low
• transverse field-annealing is much easier to conduct experimentally than perpendicular field-
• amorphous ribbons can be generally saturated
• the internal magnetic field in a sample with finite dimensions is composed of the
• the demagnetizing field normal to the ribbon plane is fairly large and, for a
• annealing temperature This is typically accomplished by a field strength of about
• transverse field-annealing In comparison transverse field-annealing can be successfully done in considerably lower fields in excess of a few hundred Oe only.
• surveillance system which can be cut into an oblong, ductile, magnetostrictive strip which can be activated and deactivated by applying or removing a pre-magnetization
• a further object is to provide such an alloy wherein the resonant frequency f r
• Another object of the present invention is to provide such an alloy which,
• Another object of this invention is to provide a magnetomechanical electronic article surveillance system which is operable with a marker having a resonator
• a resonator a marker embodying such a resonator and a magnetomechanical article surveillance system employing such a marker
• the resonator is an amo ⁇ hous magnetostrictive alloy and wherein the raw amo ⁇ hous magnetostrictive alloy is annealed in a such a way that a fine
• domain structure is formed with a domain width less than about 40 ⁇ m and that an
• anisotropy is induced which is pe ⁇ endicular to the ribbon axis and points out of the ribbon plane at an angle larger than 5° up to 90° with respect to the ribbon plane.
• the lower bound for the anisotropy angle is necessary to achieve the desired refinement of the domain structure which is necessary to reduce eddy current
• crystallinity is introduced from the top and bottom surfaces of the ribbon or
• substantially linear includes the possibility of the hysteresis
• non-linear loop triggers fewer false alarms in harmonic systems compared to
• the annealing is preferably done in such a way that the induced
• anisotropy axis is at an angle less than 90° with respect to the ribbon plane, which
• the oblique magnetic easy axis can be obtained, for example, by annealing in
• a preferred method in order to achieve the above objects therefore includes applying a magnetic annealing field whose strength (in Oe) is lower than the saturation induction (in Gauss) of the amo ⁇ hous alloy at the annealing temperature.
• This field typically 2 kOe to 3 kOe in strength, is applied at angle between about 60° and 89° with respect to a line across the ribbon width.
• This field induces a magnetic easy anisotropy axis which is parallel to the magnetization direction during annealing (which typically does not coincide with the field direction for such moderate field strengths) and which is finally oriented at angle of at least about 5-
• transition metals such as Cr and/or Mn and wherein
• compositions generally reveal a
• compositions should be generally selected which, moreover, when
• annealed in a magnetic field have an anisotropy field of less than about 13 Oe.
• composition such as Fe 24 Co 18 Ni 40 Si 2 B 16 , Fe 24 Co 16 Ni 43 Si 1 B 16 or Fe 23 Co 1s Ni 45 Si 1 B 16 , a
• saturation magnetostriction between about 5ppm and about 15ppm, and/or when
• ribbon has a thickness less than about 30 ⁇ m, a length of about 35mm to 40mm and a width less then about 13mm preferably between about 4 mm to 8 mm i.e., for
• compositions for this case have e.g. a composition such as
• Figures 1a and 1b represent a comparative example of the typical domain
• Fig. 1a is a schematic sketch of this domain
• Fig. 1b is an experimental example of this domain structure for an
• Figures 2a and 2b represent a comparative example of the typical domain
• FIG. 2a is a schematic sketch of this domain structure
• Fig. 2b is an experimental example of this domain structure for an amo ⁇ hous Fe 24 Co 18 Ni 40 Si 2 B 18 alloy annealed for about 6s at 350°C in a pe ⁇ endicular field of about 10 kOe.
• Figures 3a and 3b show the typical hysteresis loops as obtained after (a)
• dashed lines in each case are the idealized, linear loops and serve to demonstrate the linearity and the definition of the anisotropy field H k .; the particular sample shown in the figure is an amo ⁇ hous Fe 24 Co 18 Ni 40 Si 2 B 18 alloy annealed for about 6s at 350°C in each case.
• Figure 4 is a comparative example according to the prior art for the typical
• Figure 5 is an inventive example for the typical behavior of the resonant
• Figures 6a and 6b illustrate the principles of the field annealing technique according to this invention
• Fig. 6a is a schematic sketch of the ribbon's cross section (across the ribbon width) and illustrates the orientation of the magnetic field vector and the magnetization during annealing
• Fig. 6b shows the theoretically
• the field strength H is
• Figure 7 shows the temperature dependence of the saturation magnetization J s of an amo ⁇ hous Fe 24 Co 18 Ni 40 Si 2 B 18 alloy.
• Figures 8a and 8b show an example for the domain structure of an
• anisotropy oriented perpendicular to the ribbon axis and oblique to the normal of the
• Fig. 8a is a schematic sketch of this domain structure
• Fig. 8b is an
• Figures 9a and 9b show an inventive example for the (a) magnetic and (b)
• Fig. 9a shows the hysteresis loop which is linear almost up to saturation at H k
• Fig. 9b shows the resonant frequency f r
• Figure 10 compares the typical behavior of the damping factor Q '1 as a
• example is an amorphous Fe 24 Co 18 Ni 40 Si 2 B 18 alloy annealed in a continuos mode for
• FIGS 11a, 11b and 11c demonstrate the effect of the strength of the
• Fig. 11a shows the maximum resonant signal amplitude
• Fig. 11b shows the domain size and the estimated angle of the
• Fig. 11c shows the anisotropy
• region II represents one preferred embodiment of the invention. the particular
• Fig. 12a shows the typical form of the hysteresis loop in its center part when annealed in a "pe ⁇ endicular" field of a strength larger and smaller than the saturation
• Fig. 12b shows the
• FIGS 13a and 13b demonstrate the influence of the strength and the
• FIG. 13a shows the maximum resonant signal amplitude and Fig. 13b shows the
• Figure 14 demonstrates the influence of the strength and the orientation of
• Figures 15a and 15b show an example for the deterioration of the linearity of
• Fig. 15a shows the hysteresis loop and the prevailing magnetization processes
• Fig. 15b shows the resonant frequency f r
• the resonant amplitude A1 as a function of a static magnetic bias field H is a 38mm long, 6mm wide and appr. 25 ⁇ m thick strip cut
• Figures 16a and 16b show a cross section through an annealing fixture in
• Fig. 16a demonstrates how the ribbon is oriented in the magnetic field if the opening
• Fig. 16b shows a configuration
• FIGS. 17a, 17b, 17c and 17d respectively show different cross sections of
• Figure 18 is a view of a magnet system formed by a yoke and permanent
• Figures 19a and 19b show an example for continuously annealing a straight
• FIG. 19b shows a longitudinal section of the magnet system and the oven inside the magnet; the ribbon is supplied from a reel, transported through the oven by the rollers which are driven by a motor, and is finally wound on another reel with orientation of the ribbon within the magnetic field being supported by an annealing fixture 5;
• Figures 20a and 20b show the principles of a multilane annealing device according to the invention.
• Figure 21 shows the principles of a feed-back control of the annealing
• Figures 22a and 22b compare the resonant signal amplitude of an amo ⁇ hous Fe 24 Co 18 Ni 40 Si 2 B 18 alloy after annealing in a magnetic field oriented transverse to the ribbon (prior art) or at angle of about 85° between the field direction and a line
• Fig. 22a shows the maximum
• amplitude A1 and Fig. 22b shows the amplitude at the bias field where the resonant
• Figure 23 is another comparison of the resonant signal amplitude of an
• Figure 24 is a schematic representation of the signal amplitude A1 versus the
• domain widths of about 5 and 15 ⁇ m are representative for the annealing technique
• Amorphous metal alloys within the Fe-Co-Ni-Si-B system were prepared by
• the ribbons used for the experiments were 6 mm wide and
• the ribbons were annealed in a continuos mode by transporting the alloy ribbon from one reel to another reel (or alternatively to the floor) through an oven in
• the annealing was performed in ambient atmosphere.
• the annealing temperature was varied from about 300°C to about 420°C.
• An upper bound for the annealing temperature results from the Curie temperature and the crystallization temperature.
• Another upper bound for the annealing temperature results from the requirement that the ribbon is ductile enough after the heat treatment to be cut to short strips.
• the highest annealing temperature preferably should be lower than the lowest of said material characteristic temperatures. Thus, typically, the upper bound of the annealing temperature is around 420°C.
• the annealing speed can be significantly increased up to at least 20 m/min by increasing the oven length by e.g. 1m to 2m in length.
• the ribbon was transported through the oven in a straight path and was
• the pole shoes had an diameter of 100 mm and were
• the cylindrical annealing fixture (length: 300mm,
• the oven was positioned in the magnet so that the applied magnetic field was pe ⁇ endicular to the long axis of the annealing fixture and such that ribbon was cooled while still in the presence of the applied field. By turning the fixture around its long axis, the ribbon plane could be positioned at any angle with the applied magnetic field, which at the same time was pe ⁇ endicular to the ribbon axis.
• the yoke was about 400mm long with an air-gap of about 100mm.
• the field strength produced in the center of the yoke was about 2 kOe.
• the furnace, this time, was of cylindrical shape (diameter 110 mm, length 400 mm).
• a mineral insulated wire was used as the heating wire which again guaranteed the absence of an appreciable magnetic field produced by
• the heating wire was wound on a length of 300mm which gave
• annealing fixture again could be turned around its long axis, in order to position the
• This second set-up is more suitable for manufacturing than the electromagnet construction.
• the homogenous field zone can be made
• the annealed ribbon was cut to short pieces typically 38mm long.
• the hysteresis loop was measured at a frequency of 60 Hz in a sinusoidal field of
• the anisotropy field is the defined as the magnetic
• K u is the energy needed per volume unit to
• the magnetoresonant properties such as the resonant frequency f r and the
• resonant amplitude A1 were determined as a function of a superimposed dc bias
• bursts of a small alternating magnetic field oscillating at the resonant frequency with a peak amplitude of about 18 mOe.
• the on-time of the burst was about 1.6 ms with
• the signal decays exponentially after the excitation i.e. when the
• the decay time depends on the alloy composition and the heat
• treatment may range from about a few hundred microseconds up to several
• a sufficiently long decay time of at least about 1 ms is important to
• A1 or A This resonant signal amplitude will be referred to as A1 or A, respectively, in the following.
• FIGS 1a and 1b show the typical slab domain structures obtained after
• Figures 2a and 2b show the stripe domain structure with closure domains after annealing the same sample in a pe ⁇ endicular field of 15 kOe, which yields a uniaxial anisotropy pe ⁇ endicular to the ribbon plane.
• amo ⁇ hous ribbon is typically in the order of 20-30 ⁇ m, and hence, much smaller
• the ribbon width which typically is several millimeters or more. Accordingly, the
• the domain width for the case of the pe ⁇ endicular anisotropy is much smaller, typically 10 ⁇ m or less, compared to the domain width of the transverse anisotropy, which typically is about 100 ⁇ m.
• D the ribbon width for an in-plane transverse anisotropy
• Figures 3a and 3b compare the hysteresis loops associated with the domain
• Fig. 3a shows a linear behavior up to the
• the magnetization is primarily controlled by the rotation of the magnetization vector
• closure domains associated e.g. with the irregular "labyrinth" domain pattern e.g. with the irregular "labyrinth" domain pattern.
• the pe ⁇ endicular field-annealed samples can be advantageous with respect to
• t denotes the ribbon thickness
• f is the frequency
• B is the ac induction amplitude
• ⁇ ⁇ is the electrical resistivity
• J x is the component of the magnetization
• J s is the saturation magnetization
• the denominator in eq. (2b) is related to the fact that in materials with uniaxial anisotropy pe ⁇ endicular to the direction of the applied magnetic field, the
• Fig. 4 which shows the resonant frequency f r and the resonant signal amplitude of an amorphous strip annealed according to the prior art in a
• the resonant frequency is a finge ⁇ rint of the marker.
• the resonant frequency is usually subject
• the improvement of the magneto-resonant properties is primarily related to the pe ⁇ endicular anisotropy and not necessarily the technique of how this anisotropy was achieved.
• Another way of generating such an anisotropy is e.g. by partial crystallization of the surface (cf. Herzer et al. "Surface Crystallization and Magnetic Properties in Amo ⁇ hous Iron Rich Alloys", J. Magn.
• perpendicular anisotropy is that the magnetic and magneto-elastic properties are isotropic within the ribbon plane.
• transverse anisotropy component the performance of a marker or sensor using a
• pe ⁇ endicularly field-annealed sample reveals a substantially linear characteristic
• saturation magnetostriction was about ⁇ ⁇ « 29 ppm, i.e. considerably higher than that
• df-/dHj was about 1700 Hz/Oe for the alloy while the Fe 24 Co 18 Ni 40 Si 2 B 16 alloy revealed a slope of only about 600 Hz/Oe.
• FIGS. 6a and 6b illustrate the basic principles of the field annealing
• Figure 6a is a schematic illustration of the ribbon's cross section and illustrates the orientation of the magnetic field applied during annealing and the resulting orientation of the magnetization vector during
• the orientation of the magnetization vector depends upon the strength and orientation of the applied field. It is mainly determined by the balance of the
• the total energy per unit volume can be expressed as
• J s (T a ) is the spontaneous magnetization at the annealing
• ⁇ is the out-of-plane angle of the magnetization vector
• ⁇ 0 is the
• ⁇ yy is the demagnetizing across the ribbon width. The angles ⁇ and ⁇ are measured
• the magnetic field and/or the magnetization shall nominally have no appreciable vector component along the ribbon axis.
• the ribbon or strip axis means the direction along which the properties are measured i.e. along which the bias field or the exciting ac-field is essentially acting. This is preferably the longer axis of the strip. Accordingly, across the ribbon width means a direction pe ⁇ endicular to the
• elongated strips can be also prepared by slitting or punching
• ribbon axis refers to the long strip axis and not necessarily to the casting direction
• the demagnetizing factor across the ribbon width is only about N yy « 0.004 (cf. Osbome, "Demagnetizing Factors of the General
• N--. 1.
• Figure 6b shows the calculated angle of the magnetization vector during
• the field strength H is normalized to the saturation magnetization J 8 (T a ) at the
• the magnetic easy axis induced during annealing is not parallel to the applied field, but is parallel to the direction of the magnetization vector during annealing. That is, the magnetization angle ⁇ as shown
• Figure 6 corresponds to the angle of the induced anisotropy axis after annealing.
• Figure 8 illustrates the domain structure which is obtained for such an oblique
• Fig. 8a is a schematic sketch as expected from micromagnetic
• closure domains are being formed in order to reduce the magnetostatic energy arising from the
• closure domains may be absent, but in any case the domain width is reduced in order to reduce magnetostatic stray field energy.
• Fig. 6b corresponds to the closure domains A and B in Fig. 8a, respectively.
• the out-of-plane angle of the induced anisotropy can be estimated to be about 30°.
• Figure 9 shows the hysteresis loop and the magneto-resonant behavior of a similarly annealed sample. As can be seen from Fig. 9a the non-linear opening in
• transverse field annealed sample (cf. Fig. 4) in a wide range of bias fields.
• Figure 10 compares the magneto-mechanical damping factor Q '1 of the differently field annealed samples. Figure 10 clearly reveals that owing to its fine
• the oblique anisotropy leads to a significantly lower magneto-mechanical damping than in the case of the
• the annealing field was
• Figure 11a shows the influence of the annealing field strength on the
• Fig. 11b shows the corresponding variation of the domain size and the anisotropy angle ⁇ with respect to the ribbon plane.
• the pe ⁇ endicular annealing field strength is increased above about 1.0 kOe i.e.
• the inventive material can be estimated as
• ⁇ is the out-of-plane angle of the magnetization vector
• N ⁇ is the anisotropy constant
• ranges may overlap by about 0.5 kOe).
• Region I also includes the
• the domain width typically ranges between about 40 ⁇ m
• Region II corresponds to annealing fields larger than about 1 kOe but smaller than about 6 kOe, i.e. smaller than the saturation magnetization at the annealing temperature. This results in an appreciable out-of-plane anisotropy angle of at least
• Field region II actually represents one preferred
• FIG. 11c shows the behavior of the anisotropy field H k .
• the anisotropy field of the pe ⁇ endicularly annealed ribbons is about 10% smaller than the one of the transverse field annealed ribbons. This difference has been confirmed in many comparative experiments. The most likely origin of this effect is related to the closure domains being formed when the magnetic easy axis tends to
• K u is the induced anisotropy constant
• J s is the saturation magnetization
• w is the saturation magnetization
• K u is experimentally obtainable by measuring
• the ribbon thickness t can e.g. be determined by a gauge or other
• H ⁇ " 5 is the anisotropy field of a sample annealed under the same thermal
• Fig. 11b represent the thus-determined anisotropy angle which coincides well with
• Figures 12a and 12b summarize the effect of the annealing field parameters
• Fig. 12a is an enlargement of the center part
• pe ⁇ endicular field of at least about 1 kOe but below approximately the saturation
• Domain type I refers to the transverse slab domains exemplified in Fig. 1
• type II refers to the closure domain structure of Fig. 8.
• the domain width was determined in the as annealed state and after demagnetizing
• the resonant signal amplitudes for various field annealing strengths For field strengths above about 1.5 kOe the resonant susceptibility is significantly improved as the field annealing angle exceeds about 40° and approaches a maximum when
• the field is essentially pe ⁇ endicular to the ribbon plane i.e. when ⁇ approaches 90°.
• Figures 13a and 13b also demonstrate that there is virtually no significant effect of the annealing field strength on the magneto-resonant properties when a transverse (0°) field-anneal treatment according to the prior art is employed.
• Figure 14 shows the coercivity H c for the same set of parameters in order to
• linear behavior in these examples, corresponds to coercivities less than about 80 mOe. Substantial deviations from a perfect linear behavior again are only found in the samples annealed pe ⁇ endicularly at 10 and 15 kOe i.e. in a field larger than the
• annealing field is readily improved if the annealing field angle is less than about 70°
• saturation magnetization at the annealing temperature i.e. about 6 kOe in these
• the best signal amplitudes result if the field is oriented substantially pe ⁇ endicular which means annealing angles above about 60° up to about 90°, which is a preferred embodiment of the invention.
• substantially perpendicular or “close to 90°”, respectively. This terminology means that the annealing angle should be close to 90°, i.e. about 80° to 89° but not
• the magnetization at the annealing temperature being smaller than the magnetization at the annealing temperature, i.e., when the magnetization is not completely oriented normal to the plane during annealing.
• the magnetization has to be oriented in the same manner during the annealing
• the demagnetizing factor along the continuos ribbon is at least one order of magnitude less than the factor across
• magnetic easy axis will be oriented obliquely along the ribbon axis i.e. with one vectorial component pe ⁇ endicular to the plane, as desired, but with another
• Figures 15a and 15b illustrate the non-linear hysteresis loop and the poor
• the angle of the annealing field should be
• H strength and ⁇ is the out-of-plane angle of the magnetic
• J s (T a ) is the spontaneous magnetization at the
• annealing temperature T a ⁇ s (T a ) is the magnetostriction constant at the annealing
• Figures 16a and 16b give an illustrative example.
• Figures 16a and 16b show the cross section of an mechanical annealing fixture 1 which helps to orient the ribbon 2 in the oven. If the opening 3 of this fixture 1 is larger than the ribbon
• the ribbon 2 will automatically be tilted by the torque of the magnetic field
• the ribbon plane and the magnetic field is determined by the width h of the opening and the width b of the ribbon, i.e.
• annealing fixture 1 should not exceed about half of the ribbon width.
• the annealing fixture 1 should not exceed about half of the ribbon width.
• opening should be not more than about one fifth of the ribbon width.
• the ribbon to move freely through the opening the width h should be preferably at
• pe ⁇ endicular means an orientation very close to 90°, but
• pe ⁇ endicular is used by itself in the context of describing the invention. This is in
• the annealing fixture described is necessary in guiding the ribbon through the
• purpose of the annealing fixture can be to give the ribbon a curl across the ribbon
• pe ⁇ endicular field-annealing method at field strengths which are easily accessible and which at the same time yield a significant property enhancement.
• oriented substantially pe ⁇ endicular to the ribbon plane can be more than sufficient
• Such a magnet system has the advantage that it can be built with a wider gap up to about 15cm in width and at reduced magnet costs.
• Figure 18 is a three dimensional view of a magnet system which typically includes permanent magnets 7 and an iron yoke 8.
• the magnetic field in the gap 18 between the magnets has a direction along the dashed lines and has a strength of
• the magnets are preferably made of a FeNdB-type alloy
• Figure 19a shows the cross section of such a magnet system 7,8 with an
• the oven 6 should be insulated thermally such that the exterior temperature does not
• Figure 19b shows a longitudinal section of the magnet system 7,8 and the
• the ribbon 4 is supplied from a reel 1 and transported
• the annealing fixture 5 guarantees that the ribbon is transported through
• the ribbon should be subjected to the magnetic field as long it is hot. Therefore the magnet system 7,8 should be about the same length as the oven 6, preferably longer.
• the annealing fixture 5 should be at least about as long as the magnet and/or the oven, preferably longer in order to avoid property degradation
• This stress should be at least about 10 Mpa, preferably higher i.e.
• the tensile stress should therefore be kept at a controlled level within
• the aforementioned annealing fixture is also important to support the ribbon
• a ferromagnetic ribbon has a tendency
• Figures 17a -d show a more detailed view of how the cross section of said annealing fixture may look.
• the annealing fixture preferably is formed by separate upper and lower parts between which the ribbon can be placed after which these
• Figs. 17a and Fig. 17 b are intended only to guide the ribbon through the furnace.
• the annealing fixture additionally can be used to give the ribbon a curl across the ribbon
• ribbon plane is a few degrees away from the field direction which, as described
• oven 6 and preferably longer than the magnet 7,8 in order to avoid twisting or
• the annealing fixtures tested were made of ceramics or stainless steel.
• the fixture can be assembled and disassembled in situ easily which may be necessary if the ribbon breaks or when loading a new ribbon. This does not exclude, however, the suitability of a ferromagnetic material for the
• Such a ferromagnetic device could act as a kind of yoke in order to increase the magnetic field strength applied to the ribbon, which would be advantageous to reduce the magnet costs.
• Figs. 19a and 19b show only a single ribbon being transported through the oven 6.
• the annealing apparatus system should have at ieast a second lane with the corresponding supply and wind-
• Figs. 20a and 20b schematically show such a two lane system.
• Such two or multiple lane systems enhance the annealing capacity.
• the individual lanes have to be arranged in such a way that
• the individual lanes all can be put into the same oven or
• an oven of a smaller diameter can be used for each individual lane.
• the latter may be advantageous if the ribbons in the different lanes require different annealing temperatures.
• the magnetic properties like e.g. the resonant frequency or bias field for the
• a further improvement is to provide an on-line control of the magnetic properties during annealing, which is schematically sketched in Fig. 21. This can be realized by guiding the annealed ribbon 4 through a solenoid and sense coil 20 before winding it up. The solenoid produces a magnetic test field, the response of the material is recorded by the sense coil. In that way the magnetic properties can be measured during annealing and corrected to the desired values by
• control unit 21 which adjusts the annealing speed, the annealing temperature and/or the tensile stress along the ribbon, accordingly. Care should be
• a multilane oven has several such solenoids sense coils 20 such that
• the annealing parameters of each individual lane can be adjusted independently.
• the magnetic field is
• the magnet system 7,8 and the oven 6 are at Ieast about 1 m, long
• moderate strength i.e. below the saturation magnetization of the material at the annealing temperature and oriented pe ⁇ endicular to the ribbon plane i.e. more precisely at an angle between about 60° and 89° with respect to a line across the
• a field strength of about 2 kOe was used, produced by a permanent magnet system as described before.
• the magnetic field was oriented at about 85° with respect to the ribbon plane which results in an oblique anisotropy i.e. an magnetic easy axis pe ⁇ endicular to the
• the experiments were conducted in a relatively short oven as described above.
• the annealing speed was about 2 m/min which for this oven, which corresponds to an effective annealing time of about 6 seconds.
• magnetoresonant properties among others are determined by the annealing time
• H k is the anisotropy field
• H- ⁇ is the bias field where the resonant amplitude A, is maximum
• A, ⁇ is said maximum signal
• is the slope of the resonant frequency f r at H ⁇
• ⁇ m is bias field where the resonant frequency has its minimum
• A,-.*-, is the signal at said minimum
• ⁇ f r is the difference of the resonant frequency at a bias of 2 Oe and 6.5 Oe, respectively.

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