GB2291205A - Magnetic field responsive device - Google Patents
Magnetic field responsive device Download PDFInfo
- Publication number
- GB2291205A GB2291205A GB9412245A GB9412245A GB2291205A GB 2291205 A GB2291205 A GB 2291205A GB 9412245 A GB9412245 A GB 9412245A GB 9412245 A GB9412245 A GB 9412245A GB 2291205 A GB2291205 A GB 2291205A
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- GB
- United Kingdom
- Prior art keywords
- magnetic field
- layer
- gmr
- responsive device
- field responsive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y25/00—Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
- G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
- G01R33/09—Magnetoresistive devices
- G01R33/093—Magnetoresistive devices using multilayer structures, e.g. giant magnetoresistance sensors
-
- 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
- H01F1/0036—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties showing low dimensional magnetism, i.e. spin rearrangements due to a restriction of dimensions, e.g. showing giant magnetoresistivity
-
- 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
- H01F1/40—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials of magnetic semiconductor materials, e.g. CdCr2S4
- H01F1/401—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials of magnetic semiconductor materials, e.g. CdCr2S4 diluted
- H01F1/407—Diluted non-magnetic ions in a magnetic cation-sublattice, e.g. perovskites, La1-x(Ba,Sr)xMnO3
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F10/00—Thin magnetic films, e.g. of one-domain structure
- H01F10/32—Spin-exchange-coupled multilayers, e.g. nanostructured superlattices
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Power Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Nanotechnology (AREA)
- Physics & Mathematics (AREA)
- Materials Engineering (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Hall/Mr Elements (AREA)
Abstract
A magnetic field responsive device which comprises: a electrically insulating substrate 2, an electrically conductive layer on the substrate, the layer comprising a plurality of elongate strips of an electrically conductive soft magnetic material 3 and a giant magneto resistive (GMR) material 7 arranged alternately and side by side with their adjacent surfaces in electrical contact, the width of each of the strips of GMR material in the plane of the layer being not greater than twice the mean free path of an electron in the said GMR material, and the adjacent strips of soft magnetic material and GMR material having opposed directions of magnetisation in zero applied magnetic field. <IMAGE>
Description
MAGNETIC FIELD RESPONSIVE DEVICE
This invention relates to magnetic field responsive devices and is more particularly concerned with a magnetic field responsive device having improved sensitivity and performance and including one or more giant magneto resistive (GMR) materials.
A variety of magnetic field sensors have been proposed hitherto. The simplest of these are Hall Effect magnetometers in which the size of the magnetic field is derived from measurement of a transverse voltage in a current-carrying semiconductor placed in the magnetic field. Such devices are exceedingly temperature sensitive, and in fact the measured values are exponentially dependent upon temperature. Classical magneto resistive materials, such as nickel iron have also been used for stray field pick up, but such devices are too insensitive for many applications.
Flux-gate magnetometers are also used to measure magnetic fields. In these devices a soft magnetic material is excited with an AC excitation field, with the response, as modified by the ambient field, being observed.
Layered sandwich-type magneto resistive devices comprising at least two deposited layers of magnetic thin films separated by a non-magnetic thin film layer have been proposed for use as magnetic memory cells and magnetoresistive read transducer assemblies. Examples of such devices are illustrated in European Patent
Specifications Nos. 0276784 and 0314343, US Patent No.
4897288 and International Patent Application No.
W091/18424, the entire disclosures of which are incorporated herein by reference.
Giant magneto resistive (GMR) materials such as iron chromium or cobalt copper have been proposed for use in magnetic field sensors. The sensitivity of such devices incorporating GMR materials may be improved by the use of layered sandwich-type structures, but again the change in the electrical resistance at low magnetic fields is not enough for many applications. In high fields at room temperature, however, a 60% 6R/R is achievable. These devices are, nevertheless, very difficult to make consistently because any pinholes in the layers can result in non-optimal exchange coupling between the magnetic layers.
Other magneto resistive materials which have been suggested include cobalt silver, but this is a very fine grain material and inherently magnetically hard. It is only useful in devices for measuring high magnetic field strengths.
In Phys Rev Lett 71 (1993) 2331, the entire disclosure of which is incorporated herein by reference, there is described a GMR material comprising a mixed oxide of lanthanum, barium and manganese with which a & /R of 97% was achieved at room temperature in high fields.
None of the magnetic field sensors which have hitherto been proposed have achieved the combination of sensitivity, size and ease of manufacture necessary for many applications and any improvement in this respect would be highly desirable.
According to the present invention there is provided a magnetic field responsive device which comprises an electrically conductive soft magnetic material and a giant magneto resistive material proximate thereto and in electrical contact therewith.
In one aspect the invention provides a magnetic field responsive device which comprises:
an electrically insulating substrate,
an electrically conductive layer on the substrate,
the layer comprising a plurality of elongate strips of an electrically conductive soft magnetic material and a giant magneto resistive (GMR) material arranged alternately and side by side with their adjacent surfaces in electrical contact,
the width of each of the strips of GMR material in the plane of the layer being not greater than twice the mean free path of an electron in the said GMR material, and
the adjacent strips of soft magnetic material and
GMR material having opposed directions of magnetisation in zero applied magnetic field.
In another aspect the invention provides a method of manufacturing a magnetic field responsive device which comprises:
depositing an electrically conductive layer of a soft magnetic material onto a substrate,
removing thin elongate strips of the soft magnetic material at intervals so as to form vias in the layer thereby producing in the layer elongate strips or mesas of soft magnetic material electrically insulated from each other by the vias,
depositing an electrically insulating giant magneto resistive (GMR) material onto the layer so as to fill, or at least bridge the vias in the layer,
the width of each of the vias at at least one point along its length being not greater than twice the mean free path of an electron in the GMR material, and
if necessary, treating the layer such that adjacent strips or mesas of soft magnetic material and strips of
GMR material filling or bridging the vias have opposed directions of magnetisation in zero applied magnetic field.
The magnetic field responsive device can be for example a magnetic field sensor, a proximity sensor, a security device, a magneto resistive read transducer, a flux gate magnetometer or a direction finding device.
The electrically insulating substrate preferably has a smooth, and most preferably a flat surface and can comprise, for example, a glass, a plastics material or any other suitable electrically insulating layer, film or surface.
In this specification, a soft magnetic material is one which has its direction of magnetisation changed in low magnetic fields, of the order of, for example, less than about 1000Amps per metre. The electrically conducting soft magnetic material can be any suitable ferro-magnetic material or alloy, and for example very good results have been obtained with alloys of iron with for example, nickel and/or cobalt. The preferred soft magnetic material is Ni3Fe.
In principle any suitable GMR material with low electrical conductivity can be used in the devices of the invention. Preferably the GMR material is a semiconductor or an electrical insulator, for example a magnetic oxide, such as for example iron oxide, or a lanthanum, barium, manganese oxide. Particularly good results have been obtained using a lanthanum, barium, manganese mixed oxide of the type mentioned heretofore.
The strips or mesas of soft magnetic material and
GMR material strips or filled vias are arranged alternately on the substrate such that an electric current passing across the layer must pass through alternate mesas of soft magnetic material and vias of GMR material. The preferred GMR oxide materials are semiconductors or insulators and thus it is important that the width of each of the vias is sufficiently small to enable electrons to pass through the GMR material filling or bridging the via. Preferably the width of each via is not greater than one and a half times the mean free path of an electron in the GMR material, and most preferably the width is equal to or less than the mean free path of an electron in the GMR material. In general, this requires the width of the vias to be around ten to one hundred lattice spacings (0.2y) at at least one point.
The thickness of the deposited soft magnetic layer is preferably small, consistent with the layer having a suitable electrical resistance. Thicknesses of about 0.1 to about 5 microns can be used, but preferably the thickness is around 1 micron.
The width of each of the strips or mesas of soft magnetic material is preferably also small, but in this case the width is not so critical, and for example widths of from 1 to 100y have been found to be suitable for the strips or mesas of soft magnetic material.
In some preferred devices according to the invention the strips or mesas of soft magnetic material may be in intimate physical contact with the strips of GMR material although this is not essential. Adjacent surfaces of soft magnetic material and GMR material can, for example, be separated by a thin layer of an electrically conductive metallic material, for example, a noble metal such as copper, silver or gold. Where such a separation layer is used, this is preferably a "flashy layer of, for example, copper, of a few nanometres thickness.
Although the invention is not intended to be bound by any particular theory, it is believed that by arranging for the soft magnetic material and GMR material to have opposed directions of magnetisation in zero applied magnetic field the conduction of electrons through the GMR material is assisted when the magnetism of the soft magnetic material is reversed, thereby increasing the efficiency of the device. If necessary the layer may be treated to ensure that the directions of magnetisation are opposed, by, for example, applying a magnetic field of sufficient intensity to change the direction of magnetisation of the soft magnetic material in a zero applied magnetic field.
In the method of the invention the layer of soft magnetic material is preferably deposited onto the substrate by any of the known deposition techniques for example, sputtering, molecular beam epitaxy, electrodeposition or laser ablation, until a layer of about 1 micron thickness has been obtained.
The mesas and vias are preferably obtained by an etching process, and lithographic techniques such as electron beam lithography or possibly X-ray lithography can be used. In electron beam lithography a mask is first used to make a pattern on the surface and the mesas and vias formed by plasma etching. The vias need not be parallel sided, and for example it may be advantageous for the vias to become progressively narrower in width towards their bottom, that is, approaching the substrate.
It is important to arrange, however, that none of the soft magnetic material bridges the vias to avoid nonoptimal exchange coupling between the magnetic materials.
The GMR material may be deposited onto the surface of the etched layer by any suitable technique, but preferably deposition is by laser ablation. This process is highly directional and can therefore more easily fill the vias with the GMR material. Sputtering may be used in some cases, but is not usually preferred.
After the deposition of the GMR material, the entire layer may be annealed if desired, for example at a temperature of from 100 to 6000C.
A magnetic field responsive device according to the invention will now be described by way of example with reference to the accompanying Drawings in which:
Figure 1 shows a diagrammatic representation of the device in sectional side elevation; and
Figure 2 shows the device in plan view.
Referring to the Drawings, the device, illustrated generally at 1, comprises a plastics film substrate 2 having deposited thereon by a sputtering technique a thick layer 3 of nickel iron Ni3Fe. The Ni3Fe layer has etched in its surface by electron beam lithography a plurality of parallel vias 4 which extend to the surface of the substrate 2 and insulate adjacent mesas of nickel iron 5 one from another. In the device illustrated the vias are parallel-sided, but other configurations are possible, for example the vias could become narrower in the direction of the substrate 2.
On top of the nickel iron layer 3 there is deposited by laser ablation a GMR material layer 6 which comprises a mixed oxide of lanthanum, barium and manganese. As shown in Figure 1 the vias can be completely filled with
GMR material as in 7, but this is not essential, and the
GMR material could only partially fill the via or simply form a bridge between adjacent mesas as illustrated in 8.
Electrical connections 9, 10 are made to the nickel iron layer, which extend to a current source 11 and a voltmeter 12.
In operation the device is placed in the magnetic field whose intensity is to be measured and the current source switched on. Generally an applied current of about milliamps will be suitable. The effect of the magnetic field intensity alters the number of electrons which can pass through the GMR material and thus alters the apparent resistivity. The change in potential is measured by the voltmeter and is directly related to field intensity.
As illustrated, the sensitivity of the device is greatest in a direction lying along the mesas. The dimensions of the device can, however, be chosen to give extreme directionality, or relative non-directionality, as desired.
The reader's attention is directed to all papers and documents which are filed concurrently with this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
All the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps or any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
Claims (24)
1. A magnetic field responsive device which comprises:
a electrically insulating substrate,
an electrically conductive layer on the
substrate,
the layer comprising a plurality of elongate
strips of an electrically conductive soft magnetic
material and a giant magneto resistive (GMR)
material arranged alternately and side by side with
their adjacent surfaces in electrical contact,
the width of each of the strips of GMR material
in the plane of the layer being not greater than
twice the mean free path of an electron in the said
GMR material, and
the adjacent strips of soft magnetic material
and GMR material having opposed directions of
magnetisation in zero applied magnetic field.
2. A magnetic field responsive device according to
Claim 1, which is a magnetic field sensor, a
proximity sensor, a security device, a magneto
resistive read transducer, flux-gate magnetometer,
or a direction finding device.
3. A magnetic field responsive device according to
Claim 1 or 2, in which the substrate comprises a
flat surface of a glass or plastics material.
4. A magnetic field responsive device according to any
of the preceding claims, in which the soft magnetic
material comprises a ferro-magnetic material or
alloy.
5. A magnetic field responsive device according to
Claim 4, in which the soft magnetic material is
nickel iron.
6. A magnetic field responsive device according to any
of the preceding claims, in which the GMR material
is a magnetic oxide.
7. A magnetic field responsive device according to
Claim 6, in which the magnetic oxide is iron oxide
or a lanthanum barium manganese oxide.
8. A magnetic field responsive device according to any
of the preceding claims, in which the strips of
electrically conductive soft magnetic material and
GMR material are arranged respectively in a series
of alternating mesas and vias.
9. A magnetic field responsive device according to
Claim 8, in which the width of each via is equal to
or less than the mean free path of an electron in
the GMR material.
10. A magnetic field responsive device according to
Claim 8 or 9, in which the width of each of the vias
is from about 10 to about 100 lattice spacings at at
least one point.
11. A magnetic field responsive device according to any
of the preceding claims, in which the thickness of
the strips of electrically conductive soft magnetic
material is from about 0.1 to about 5y.
12. A magnetic field responsive device according to any
of the preceding claims, in which the width of each
of the strips of soft magnetic material is from 1 to 100cm.
13. A magnetic field responsive device according to any
of the preceding claims, in which the strips of soft
magnetic material are in intimate physical contact
with the strips of GMR material.
14. A magnetic field responsive device according to any
of Claims 1 to 12, in which adjacent surfaces of the
soft magnetic material and the GMR material are
separated by a thin layer of an electrically
conductive metallic material.
15. A magnetic field responsive device according to
Claim 14, in which the separation layer comprises a
noble metal.
16. A magnetic field responsive device substantially as
hereinbefore described with reference to and as
illustrated in the accompanying Drawings.
17. A magnetic field responsive device substantially as
hereinbefore described.
18. A method of manufacturing a magnetic field
responsive device which comprises:
depositing an electrically conductive layer of
a soft magnetic material onto a substrate,
removing thin elongate strips of the soft
magnetic material at intervals so as to form vias in
the layer thereby producing in the layer elongate
strips or mesas of soft magnetic material
electrically insulated from each other by the vias,
depositing an electrically insulating giant
magneto resistive (GMR) material onto the layer so
as to fill, or at least bridge the vias in the
layer,
the width of each of the vias at at least one
point along its length being not greater than twice
the mean free path of an electron in the GMR
material, and
if necessary, treating the layer such that
adjacent strips or mesas of soft magnetic material
and GMR material filling or bridging the vias have
opposed directions of magnetisation in zero applied
magnetic field.
19. A method according to Claim 18, in which the layer
of soft magnetic material is deposited onto the
substrate by sputtering, molecular beam epitaxy,
electrodeposition, or laser ablation.
20. A method according to Claim 18 or 19, in which the
mesas and vias are obtained by a lithographic
etching process.
21. A method according to any of Claims 18 to 20, in
which the GMR material is deposited onto the surface
of the etched layer by laser ablation.
22. A method according to any of Claims 18 to 21, in
which, after the deposition of the GMR material, the
layer is annealed by heating to a temperature of
from 100 to 6000C.
23. A method according to any of Claims 18 to 22, in
which a magnetic field is applied to the layer of
sufficient intensity to change the direction of
magnetisation of the soft magnetic material in a
zero applied magnetic field such that the directions
of magnetisation of the soft magnetic material and
the GMR material are opposed.
24. A method according to any of Claims 18 to 23
substantially as hereinbefore described.
Priority Applications (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9412245A GB2291205A (en) | 1994-06-18 | 1994-06-18 | Magnetic field responsive device |
| AU27919/95A AU2791995A (en) | 1994-06-18 | 1995-06-13 | Magnetic field responsive device |
| US08/750,689 US5886523A (en) | 1994-06-18 | 1995-06-13 | Magnetic field responsive device having giant magnetoresistive material and method for forming the same |
| EP95923319A EP0766831A1 (en) | 1994-06-18 | 1995-06-13 | Magnetic field responsive device |
| JP8501629A JPH10503883A (en) | 1994-06-18 | 1995-06-13 | Magnetic field response device |
| PCT/EP1995/002281 WO1995035507A1 (en) | 1994-06-18 | 1995-06-13 | Magnetic field responsive device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9412245A GB2291205A (en) | 1994-06-18 | 1994-06-18 | Magnetic field responsive device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9412245D0 GB9412245D0 (en) | 1994-08-10 |
| GB2291205A true GB2291205A (en) | 1996-01-17 |
Family
ID=10756935
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9412245A Withdrawn GB2291205A (en) | 1994-06-18 | 1994-06-18 | Magnetic field responsive device |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2291205A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0777212A3 (en) * | 1995-11-30 | 1998-01-28 | Nec Corporation | Magnetometric sensor with two magnetically isolated regions formed of spin-polarized materials and magnetic head using the same |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0565102A2 (en) * | 1992-04-10 | 1993-10-13 | Hitachi Maxell, Ltd. | Magnetic laminations and magnetic heads and magnetic recording/reproducing devices using a magnetic lamination |
-
1994
- 1994-06-18 GB GB9412245A patent/GB2291205A/en not_active Withdrawn
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0565102A2 (en) * | 1992-04-10 | 1993-10-13 | Hitachi Maxell, Ltd. | Magnetic laminations and magnetic heads and magnetic recording/reproducing devices using a magnetic lamination |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0777212A3 (en) * | 1995-11-30 | 1998-01-28 | Nec Corporation | Magnetometric sensor with two magnetically isolated regions formed of spin-polarized materials and magnetic head using the same |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9412245D0 (en) | 1994-08-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |