US3470550A - Synthetic bulk element having thin ferromagnetic film switching characteristics - Google Patents

Synthetic bulk element having thin ferromagnetic film switching characteristics Download PDF

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US3470550A
US3470550A US646638A US3470550DA US3470550A US 3470550 A US3470550 A US 3470550A US 646638 A US646638 A US 646638A US 3470550D A US3470550D A US 3470550DA US 3470550 A US3470550 A US 3470550A
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layers
magnetizable
magnetization
axis
field
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Paul E Oberg
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Unisys Corp
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Sperry Rand Corp
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
    • G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
    • G11C11/14—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using thin-film elements
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
    • G11C11/14—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using thin-film elements
    • G11C11/15—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using thin-film elements using multiple magnetic layers

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  • the thin-ferromagnetic-film layers preferably possess low anisotropic fields H with portions of alternate layers having a high coercivity H for functioning as permanent magnets.
  • the permanent magnet portions having their magnetization aligned along a SN permanent magnetic axis M bias the magnetization of the low H anisotropic regions: to become aligned With the polarization of the magnetization of the permanent magnet portions; or to become rotated out of alignment with their easy axes that are orthogonal to the axis M
  • Operation as a transformer, or inductor core is achieved by the application and detection of an AC field along a magnetic axis that is orthogonal to the axis M and to the easy axis of the low H anisotropic regions while operation as a memory core is achieved by the application of drive fields and the detection of switching fields along a magnetic axis that is orthogonal to the axis M but parallel to the orthogonally oriented easy axes of the low H anisotropic regions.
  • the present invention relates to magnetizable elements comprising a plurality of stacked, magnetizable layers of thin-ferromagnetic-films, each layer possessing singledomain property.
  • the term single-domain property may be considered the magnetic characteristic of a three-di mensional element of magnetizable material having a thin dimension that is substantially less than the Width and length thereof wherein no magnetic domain walls can exist parallel to the large surfaces of the element.
  • Such layers may, or may not, possess the magnetic characteristic of unaxial anisotropy providing an easy axis along which the remanent magnetization thereof lies in a first or a second and opposite direction.
  • magnetizable material shall designate a substance having a remanent magnetic fiux density that is substantially high, i.e., approaches the flux density at magnetic saturation. It is desirable that each of the several thin-ferromagneticfilm layers layers that make up the magnetizable element possess such single-domain property whereby singledomain rotational switching of the magnetization M of such magnetizable element shall be achieved in a manner such as described in the S. M. Rubens et al., Patent No. 3,030,612.
  • Such magnetizable elements may be fabricated in a continuous vapor deposition process such as disclosed in the S. M. Rubens et al., Patent No. 2,900,282 and Patent No. 3,155,586. However, such magnetizable elements may be formed by any one of the plurality of well known methods of fabricating magnetizable memory elements, e.g., cathodic sputtering.
  • magnetizable element that is capable of operating in a single-domain manner while providing substantially larger external magnetic fields, or closed path flux, that, upon the switching or rotation of the elements magnetization M, couple the lines associated therewith producing an output signal therein that is of a substantially larger magnitude than that achieved by a single thin-ferromagnetic-film layer.
  • Prior art arrangements of magnetizable elements operating as a single element have comprised a plurality of stacked, similar magnetizable layers of thin-ferrornagnetic-films separated by interstitial layers of insulating material involving all such magnetizable. elements wherein the easy axes of all of the thin-ferromagnetic-film layers thereof are aligned with the materials thereof being similar.
  • Prior art arrangements of magnetizable elements operating as a single element comprise a plurality of stacked, similar magnetizable layers of thin-ferromagneticfilms separated by interstitial layers of insulating material that are fabricated with the easy axes of all magnetizable layers aligned.
  • the magnetizable layers should rotate in a single-domain manner it is essential that the total thickness of the magnetizable element be limited to a substantially thin dimension. The reason for this is that when the magnetization M in the many magnetizable layers rotates such layers magnetization M vectors rotate in the same direction.
  • the components of M that are perpendicular to the major surfaces of the layers are all in the same aligned direction through the thickness thereof tending to be continuous in the magnetizable and insulating layers.
  • internal pole pairs i.e., on opposite surfaces on each insulating layer, tend to cancel out each other leaving only the oles on the top and bottom layers uncancelled.
  • This results in a small demagnetizing field i.e., the field applied to the magnetizable layer that tends to demagnetize the layers normal magnetization for the large thickness that is produced by the many magnetizable and insulating layers.
  • This small demagnetizing field approaches that of bulk magnetizable material of the same thickness causing the magnetizable layers to switch in a manner similar to bulk material switching.
  • the magnetization M in the adjacent magnetizable layers rotate in opposite directions whereby the components of M that are perpendicular to the major surfaces of the layers are in opposite, but aligned directions perpendicular to the thickness of the element.
  • the internal ole pairs do not tend to cancel out each other.
  • This large demagnetizing field forces the magnetization M of the individual magnetizable layers to switch in a single-domain manner similar to that achieved by magnetizable elements of a single thin-ferromagnetic-film layer.
  • this large demagnetizing field is present the magnetization M vector remains essentially in the plane of the magnetizable layer during its rotation. This is a requirement, and the reason, for the high speed change in magnetization provided by singledomain films.
  • the present invention is an improvement of such above prior art arrangements of magnetizable elements comprising a plurality of stacked, similar magnetizable layers of thin-ferromagnetic-films that are separated by interstitial layers of insulating material.
  • All of the magnetizable layers of the present invention are preferably of substantially the same thickness and possess the magnetic characteristic of single-domain roperty. Additionally, all of the magnetizable layers of the present invention are of substantially the same material except that portions of alternate layers of the thin-ferromagnetic-films have a high coercivity H e.g., H l oersteds for an approximately 90% C0-10% Fe layer, for functioning as permanent mag- -*nets.
  • the permanent magnet portions of these alternate layers have their magnetization aligned along a SN permanent magnet axis M providing a biasing field aligned parallel, in the same direction, in the remaining low anisotropic portion of the layer having the high coercivity portion, but aligned antiparallel, or NS, in the low anisotropic other alternate layer.
  • alternate magnetizable layers forming a first set of layers are formed having a first high coercivity H portion and a second low anisotropic field H portion
  • the other alternate magnetizable layers forming a second set of layers are formed with a low anistropic field H e.g., H 4.0 oersteds for an approximately 80% Ni-20% Fe layer.
  • the magnetizable elements of the present invention are presented as having two preferred embodiments: one having the ability to be operated as a transformer, or inductor, core; while the second embodiment has the ability to be operated as a bistable memory core.
  • operation is achieved by the application of an AC driving field along a magnetic axis that is orthogonal to the permanent magnet axis M of the first set of layers and to the easy axis of the low I-I material portion while detection of the AC field is also achieved along the magnetic axis that is orthogonal to such permanent magnet axis M and to the easy axis of the low H material portion.
  • Operation as a bistable memory core is achieved by the utilization of device that is similar to that utilized as an inductor core in that the device to be utilized as a bistable memory core is preferably fabricated having low values of unaxial anisotropy H providing a low H easy axes in the low anisotropic field H regions, those regions other than the permanent magnet regions, that are orthogonal to the permanent magnet axis M
  • Operation of this second embodiment as a bistable memory core is achieved by the application of a drive field along a magnetic axis that is orthogonal to the permanent magnetic axis M or parallel to the easy axis of the associated low anisotropic field region, while readout is achieved by the detection of a switching field along a magnetic axis that is orthogonal to the magnetic axis M or parallel to such easy axis of the low anisotropic field region.
  • Drive and sense lines, or windings, that are magnetically, or conductively, coupled tot he magentizable elements of the present invention may be of the well known printed circuit type as particularly adapted in bistable memory core operation or more conventional transformer winding techniques when operated as an inductor core.
  • FIG. 1 is a side view of a magnetizable element of a plurality of magnetizable layers separated by interstitial layers of insulating material as proposed by the present invention.
  • FIG. 2 is a plan view of the magnetizable element of FIG. 1 illustrating the construction and orientation of the permanent magnet axis M of the high coercivity region.
  • FIG. 3 is a schematic illustration of the related vectors involved in the switching mechanism of adjacent magnetizable layers as proposed by the present invention.
  • FIG. 4 is a plan view of a magnetizable element of the present invention illustrating the orientation of the permanent magnet axis M and of the magnetization M of the low anisotropic field regions of the inductor core.
  • FIG. 5 is a plan view of a magnetizable element of the present invention illustrating the orientation of the ermanent magnet axis M and the magnetization M of the low anisotropic field regions of the bistable memory core.
  • FIG. 6 is a composite illustration of the B-H loop characteristics of the magnetizable elements of FIG. 4 and of FIG. 5.
  • Magnetizable element 10 is comprised of a substrate 12 and a plurality of magnetizable layers 14, 16 insulatively separated by a plurality of insulating layers 18. Magnetizable element 10 is particularly adaptable to be fabricated in successive deposition steps of alternate layers of magnetizable material and insulating material in an evacuatable enclosure. Magnetizable element 10 is preferably fabricated in a continuous vapor deposition process such as disclosed in the S. M. Rubens et al. Patents Nos. 2,900,- 282 and 3,155,561 or the A. V. Pohm Patent No. 3,065,- 105. The multi-layer element 10 may be deposited upon a substrate 12 of many well known materials such as glass or metal.
  • All of the magnetizable layers of the present invention are preferably of substantially the same thickness and possess the magnetic characteristic of single-domain property whereby by the application of the proper drive fields single-domain rotational switching of the magnetization of such layers may be achieved in the manner such as described in the S. M, Rubens Patent No. 3,030,612. Additionally, all of the magnetizable layers of the present invention are of substantially the same material except that alternate layers 14 have a high coercivity H portion 20 for functioning as a permanent magnet. The remaining portions 22 of magnetizable layers 14 and all of the magnetizable layers 16 being of substantially the same material; preferably being lo'w anisotropic field I-I materials.
  • the permanent magnet portions 20 of alternate layers 14 have their magnetization permanently aligned along a S-N permanent magnet axis M providing a biasing field aligned in the same direction in the remaining low anisotropic portions 22 of layers 14 but aligned antiparallel, or NS, in the low anisotropic alternate layers 16.
  • alternate magnetizable layers 14a, 14b, 14c and 14d forming a first set of layers are formed having a first high coercivity H portion and a second low anisotropic field H portion while the other alternate magnetizable layers 16a, 16b, 16c and 16d forming a second set of layers are formed with a low anisotropic field H
  • the magnetizable element 10 of FIG. 1 for purposes of illustrating the orientation of the permanet magnet axis M associated with portions 20 of layers 14.
  • the distance between the center of the feathering edge E to the edge of element 10, noted as L may be much less than /3 of L
  • the low anisotropic field portions may be of approximately Fe-20% Ni having an H equal to three oersteds (3 oe.) while the high coercivity portions 20 of layers 14 may be of high percentage of Cobalt having an H, of 10 oersteds (l0 oe.) or greater. Note: For ease of subsequent discussion, the
  • the present invention relates to a magnetizable element that comprises a plurality of: stacked, superposed, magnetizable layers of thin-ferromagnetic-films separated by interstitial layers of insulating; material.
  • thelow anisotropic field H magnetizable layers possess the,
  • each of the layers of low anisotropic field H magnetizable material, such as portion 21) of layer 14 and adjacent layer 16 possess single-domain properties that are capable of having their magnetization switched, or rotated, in a single-domain manner such as disclosed in the above referenced S. M. Rubens et al. Patent No. 3,030,612.
  • the magnetization M as in magnetizable layer 16 is affected by an applied drive field H along the mean axis M,,, or line 32, in the plane of the layer the magnetization M is induced to rotate in the direction away from the applied drive field H toward a position M through an angle
  • the demagnetizing field of the magnetizable layer 16 limits this normal component to extremely small values causing the magnetization M to rotate through path 30 which path is substantially in the plane of layer 16. This mechanism is more fully discussed in the text Amplifier and Memory Devices: With Films and Diodes McGraw-Hill Book Company, 1965, chapter 13.
  • an applied drive field H would cause the magnetization M of all such layers 16 to rotate in the same direction.
  • the components M that are perpendicular to the major surfaces of layer 16 are all in the same aligned direction through the plurality of layers tending to be continuous therethrough.
  • these adjacent layers 16 would form internal pole pairs with respect to adjacent layers 16, such as components M that tend to cancel out each other leaving only the poles on the top and bottom layers 16 uncancelled.
  • This very small demagnetizing field approaches that of bulk magnetizable material of the same thickness causing the magnetization of the plurality of magnetizable layers 16 to switch in a manner similar to that of bulk material.
  • magnetizations M and M of layers 14 and 16, respectively are forced to rotate in opposite directions.
  • magnetization M of layer 14 would rotate in a clockwise direction (as viewed from above) along a path 34 while magnetization M in layers 16 would rotate in a counterclockwise direction along path 30.
  • the vertical components M and M generated by the rotation of magnetization M and M of layers 14 and 16, respectively, due to the opposite directions of rotation, would be of substantially equal magnitude but of opposite polarity.
  • the magnetization in the adjacent magnetizable layers 14 .and 16 rotate in opposite directions whereby the components of M that are perpendicular to the major surfaces of the layers are in opposite, but aligned, directions through the thickness of the magnetizable element provided by the plurality of pairs of layers 14, 16 and the associated insulating layers 18see FIG. 1.
  • the internal pole pairs i.e., the M components M and M that are perpendicular to the major surfaces of the layers 14 and 16 do not tend to cancel out each other. This results in a very large demagnetizing field for the large thickness produced by the many magnetizable layers 14, 16 and insulating layers 18.
  • This large demagnetizing field forces the magnetization M of the individual magnetizable layers 14, 16 to switch in a single-domain manner similar to that achieved by magnetizable elements of a single thin-ferromagnetic-film layer.
  • this large demagnetizing field is present the magnetization M vector of each layer 14, 16 remains essentially in the plane of the associated magnetizable layer 14, 16; this is a requirement, and the reason, for high speed rotational change in magnetization.
  • FIG. 4 there is illustrated a plan view of a magnetizable element 10a illustrating the orientation of the easy axes M M along line 44 formed by the low anisotropic regions of magnetizable layers 14, 16, respectively, and the permanent magnet axis M along line 44 formed by the high coercivity portions 20 of layers 14.
  • a permeable layer having a permeability a greater than that of air i.e., 21, and with substantially no remanent magnetization could function as a transformer, or inductor, core. In this arrangement of FIG.
  • the permanent magnet portions 20 of layers 14 having a permanent magnet axis M force the magnetization of the low anisotropic regions 22 to be aligned therewith along line 44 and the magnetization of layers 16 to be aligned antiparallel thereto along line 44.
  • FIG. 1 illustrates that adjacent pairs of cores 14, 16 function as high permeability substantially closed flux return paths for each other.
  • magnetizable element 10a as an inductor core is achieved by the application and detection of an AC field along a magnetic axis that is orthogonal to the antiparallel magnetization M M and the permanent magnet axis M
  • the AC magnetizing field :H applied along the axis 42 by winding 40 causes the magnetization on M M associated with layers 14, 16 to oscillate about the axis 44 through the respective angles 6 6
  • the flux variations of magnetizable element 113a due to the oscillation of the magnetizations M M about axis 44, is detected along magnetic axis 42 by winding 46; as an inductor core only one winding 40 is required. although the two windings 4t), 46 are illustrated for operation as a transformer core.
  • windings 40 and 46 function as primary and secondary windings, respectively, that are inductively coupled to the magnetizable element 10,.
  • loop 60 that is an approximate representation of the magnetic flux path traversed by the magnetic flux of magnetizable element 10a when operated in the transformer mode as described with particular reference to FIG. 4.
  • Loop 60 represents the substantially lossless operation of magnetizable element 16a such as is usually associated with the operation of thin-ferromagnetic-film layers when driven in the hard direction.
  • loop 62 represents the approximate path traversed by the magnetic flux of element 1% when operated as a memory element in accordance with the embodiment of FIG. 5.
  • Loops 60 and 62 of FIG. 6 are typical BH loops of thin-ferromagnetic-film elements having unaxial anisotropy and being driven in the hard and easy directions, respectively.
  • FIG. 5 there is illustrated a plan view of a magnetizable element b when utilized as a memory element.
  • the magnetization of the high coercivity portions of layers 14 are aligned along the NS permanent magnet axes M while the magnetization M M associated with the low anisotropic regions 22 of layers 14 and of layers 16, respectively, are parallel aligned along an easy axis 52 which is orthogonal to the permanent magnet axis M
  • the magnetization thereof, M M would normally be aligned therealong.
  • the hard direction biasing fields provided by the magnetization of regions 20 of layers 14, being in antiparallel directions in adjacent layers 14-, 16, cause the magnetization thereof.
  • M M to be biased, ,8 fi out of alignment with their easy axes 52, respectively.
  • magnetizable element 10! of FIG. 5 as a memory element, or bistable core is achieved by the application of a drive field iH; where +H may be representative of a storing of a 1 and H may be representative of the storing of a O in memory element 10b.
  • This drive field H is coupled to memory element 10b by means of coil 50 providing a drive field H that is oriented parallel to magnetic axis 52 but orthogonal to permanent magnet axis M
  • the applied drive field H is of an intensity in the area of magnetizable element 10b approximating H causing the magnetization M and M to be rotated less than 180, e.g., 120, to assume a magnetization polarization along their oppositely biased axes, e.g., from 1 to 0.
  • the magnetic flux change in magnetizable element 1012 due to the substantial or insubstantial rotation, e.g., from 1 to 0 or from 0 to 0 of the magnetization M M is detected by the output, or sense, coil 56, whose magnetic axis is oriented parallel to the magnetic axis 52, inducing a signal therein that is representative of the informational state of magnetizable element 10b.
  • the output, or sense, coil 56 whose magnetic axis is oriented parallel to the magnetic axis 52, inducing a signal therein that is representative of the informational state of magnetizable element 10b.
  • loop 62 that describes the magnetic flux path traversed by the magnetic flux of magnetizable element 10! when operated as a memory core in accordance with the embodiment of FIG. 5. It can be seen that loop 62 has a substantially rectangular form that approaches the ideal characteristic for a magnetizable memory element.
  • a synthetic bulk element operating in a single domain rotational mode comprising:
  • said first set formed by alternate ones of said layers
  • said second set formed by alternate ones of said layers
  • the layers of said first set having a first high coercivity material region and a second low anisotropic field material region;
  • the layers of said second set being of a low anisotropic field material
  • the first regions of the layers of said first set permanently magnetized along a permanent magnet axis M the magnetization of the first regions of the layers of the first set biasing the magnetization of the low anisotropic field material regions of the layers of said first and second sets toward alignment with said permanent magnet axis M input and output means inductively coupled to said layers having a magnetic axis that is orthogonal to said permanent magnet axis M said input means coupling a drive field +H to said layers for causing the magnetizations of said first and second sets to rotate in a single-domain manner in opposite directions about said permanent magnet axis M for inducing a signal in said output means.
  • a substantially lossless inductor comprising:
  • said first set formed by alternate ones of said magnetizable layers
  • said second set formed by alternate ones of said magnetizable layers, other than those of said first set;
  • the layers of said first set having a first high coercivity material region and second low anisotropic field material region;
  • the layers of said second set being of a low anisotropic field material
  • the first regions of the layers of said first set permanently magnetized along a permanent magnet axis M the magnetization of the first regions of the layers of the first set biasing the magnetization of the low anisotropic field material regions of the layers of said first and second sets into alignment with said permanent magnet axis M and in an anti-parallel relationship with each other;
  • input and output means inductively coupled to said magnetizable layers having a magnetic axis that is orthogonal to said permanent magnet axis M said input means coupling a drive field :H to said magnetizable layers for causing the magnetization of said first and second sets to oscillate in a singledomain manner opposite directions about said permanent magnet axis M for inducing a signal in said output means.
  • a bistable memory operable in a single domain rotational mode comprising:
  • said first set formed by alternate ones of said magnetizable layers
  • said second set formed by alternate ones of said magnetizable layers, other than those of said first set;
  • the layers of said first set having a first high coercivity material region and a second w anisotropic field material region;
  • the layers of said second set being of a low anisotropic field material

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  • Measuring Magnetic Variables (AREA)
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US646638A 1967-06-16 1967-06-16 Synthetic bulk element having thin ferromagnetic film switching characteristics Expired - Lifetime US3470550A (en)

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JP (1) JPS5025296B1 (enrdf_load_stackoverflow)
DE (1) DE1764482A1 (enrdf_load_stackoverflow)
FR (1) FR1581575A (enrdf_load_stackoverflow)
GB (1) GB1237905A (enrdf_load_stackoverflow)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3577134A (en) * 1969-09-16 1971-05-04 Sperry Rand Corp Method of operating a convertible memory system
US3673581A (en) * 1970-02-27 1972-06-27 Hitachi Ltd Plated magnetic wire
US4845454A (en) * 1986-07-29 1989-07-04 Toko, Inc. Inductance element with core of magnetic thin films

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3095555A (en) * 1961-02-13 1963-06-25 Sperry Rand Corp Magnetic memory element
US3375091A (en) * 1964-03-17 1968-03-26 Siemens Ag Storer with memory elements built up of thin magnetic layers

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3095555A (en) * 1961-02-13 1963-06-25 Sperry Rand Corp Magnetic memory element
US3375091A (en) * 1964-03-17 1968-03-26 Siemens Ag Storer with memory elements built up of thin magnetic layers

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3577134A (en) * 1969-09-16 1971-05-04 Sperry Rand Corp Method of operating a convertible memory system
US3673581A (en) * 1970-02-27 1972-06-27 Hitachi Ltd Plated magnetic wire
US4845454A (en) * 1986-07-29 1989-07-04 Toko, Inc. Inductance element with core of magnetic thin films

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FR1581575A (enrdf_load_stackoverflow) 1969-09-19
DE1764482A1 (de) 1972-03-30
GB1237905A (enrdf_load_stackoverflow) 1971-07-07
JPS5025296B1 (enrdf_load_stackoverflow) 1975-08-22

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