# US 2018/0025840 A1 · Permanent magnet comprising a stack of n patterns

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- Number: US 2018/0025840 A1
- Document ID: US20180025840A1
- Status: Published application
- Kind: A1
- Application number: 15/654,115
- Filed: 2017-07-19
- Published: 2018-01-25
- Earliest claimed: 2016-07-20
- Assignees: Commissariat A L'energie Atomique Et Aux Energies Alternatives
- Applicants: Commissariat a l'energie atomique et aux energies alternatives
- Inventors: Bertrand DELAET; Sophie GIROUD; Rachid HIDA
- Web page: https://patentgrep.com/patent/US20180025840A1

## CPC

- H01F 41/0253: {for manufacturing permanent magnets}
- G01R 33/0052: {Manufacturing aspects; Manufacturing of single devices, i.e. of semiconductor magnetic sensor chips (devices based on galvano-magnetic effect or the like H10N50/85)}
- G01R 33/0286: {comprising microelectromechanical systems [MEMS] (MEMS devices in general B81B)}
- G01R 33/038: using permanent magnets, e.g. balances, torsion devices
- H01F 1/0009: {Antiferromagnetic materials, i.e. materials exhibiting a Néel transition temperature (H01F1/0036 takes precedence)}
- H01F 10/30: characterised by the composition of the intermediate layers {, e.g. seed, buffer, template, diffusion preventing, cap layers (H01F10/06 and H01F10/32 take precedence)}
- H01F 10/3218: {Exchange coupling of magnetic films via an antiferromagnetic interface (H01F10/3268 takes precedence)}
- H01F 10/3272: {by use of anti-parallel coupled [APC] ferromagnetic layers, e.g. artificial ferrimagnets [AFI], artificial [AAF] or synthetic [SAF] anti-ferromagnets}
- H01F 41/30: for applying nanostructures, e.g. by molecular beam epitaxy [MBE]
- H01F 41/304: {using temporary decoupling, e.g. involving blocking, Néel or Curie temperature transitions by heat treatment in presence/absence of a magnetic field}
- H01F 7/021: {Construction of PM (H01F7/0278 takes precedence; PM compositions H01F1/032)}
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

A permanent magnet including, at least once per group of ten consecutive ferromagnetic layers, a growth layer directly interposed between a top antiferromagnetic layer of a previous pattern and a bottom antiferromagnetic layer of a following pattern. This growth layer is entirely realized in a nonmagnetic material chosen from the group made up of the following metals: Ta, Cu, Ru, V, Mo, Hf, Mg, NiCr and NiFeCr, or it is realized by a stack of several sublayers of nonmagnetic material disposed immediately on one another, at least one of these sublayers being entirely realized in a material chosen from the group. The thickness of the growth layer is greater than 0.5 nm.

## Claims

### Claim 1

A permanent magnet comprising a stack of N patterns stacked one on top of another in a stack direction, where N is a whole number greater than or equal to two, each pattern comprising:
a bottom antiferromagnetic layer,
a top antiferromagnetic layer, and
a ferromagnetic layer situated between the bottom and top antiferromagnetic layers and whose direction of magnetization is frozen, by an exchange coupling, with the bottom or top antiferromagnetic layer of this said pattern,
the directions of magnetization of the ferromagnetic layers which are coupled by exchange coupling with the bottom or top antiferromagnetic layer of the same pattern being all identical to each other,
wherein:
at least once per group of ten consecutive ferromagnetic layers whose directions of magnetization are frozen by exchange coupling, the stack comprises a growth layer interposed between the top antiferromagnetic layer of the previous pattern and the bottom antiferromagnetic layer of the following pattern in the stack direction and this said growth layer is directly in contact with said two top and bottom antiferromagnetic layers between which it is interposed,
said growth layer is entirely realized in a nonmagnetic material chosen from the group made up of the following metals: Ta, Cu, Ru, V, Mo, Hf, Mg, NiCr and NiFeCr, or it is realized by a stack of several sublayers of nonmagnetic material disposed immediately on one another in the stack direction, at least one of said sublayers, known as the “metallic sublayer”, being entirely realized in a material chosen from said group, and
the thickness of the growth layer is greater than 0.5 nm.

### Claim 2 (depends on 1)

The magnet according to claim 1, wherein the antiferromagnetic layer comprises manganese and the growth layer comprises tantalum.

### Claim 3 (depends on 1)

The magnet according to claim 1, wherein the growth layer is realized by the stack of several sublayers of non-magnetic material deposited immediately on one another in the stack direction and the metallic sublayer is directly in contact with the antiferromagnetic layer of the next pattern in the stack direction.

### Claim 4 (depends on 3)

The magnet according to claim 3, wherein at least one of the sublayers of the stack is entirely composed of oxide or nitride.

### Claim 5 (depends on 1)

The magnet according to claim 1, wherein the number N is greater than or equal to five or ten.

### Claim 6 (depends on 1)

The magnet according to claim claim 1, wherein the stack comprises a growth layer interposed between two consecutive patterns of the stack at least once per group of four consecutive ferromagnetic layers whose directions of magnetization are frozen by exchange coupling.

### Claim 7 (depends on 6)

The magnet according to claim 6, wherein the stack comprises a growth layer interposed between each pattern.

### Claim 8 (depends on 1)

The magnet according to claim 1, wherein the pattern comprises a bottom antiferromagnetic layer and a top antiferromagnetic layer and the ferromagnetic layer is interposed between the bottom and top antiferromagnetic layers, the direction of magnetization of the ferromagnetic layer being frozen, by an exchange coupling with the bottom and top antiferromagnetic layers of said pattern.

### Claim 9 (depends on 1)

The magnet according to claim 1, wherein at least one of the patterns comprises a supplemental ferromagnetic layer whose direction of magnetization is trapped solely by RKKY (Ruderman-Kittel-Kasuya-Yosida) coupling with another ferromagnetic layer.

### Claim 10 (depends on 1)

The magnet according to claim 1, wherein at least one of the ferromagnetic layers comprises:
a first sublayer realized in CoFeB whose thickness is greater than 0.05 nm, and
a second sublayer realized in a ferromagnetic material different from CoFeB and whose thickness is greater than the thickness of the first sublayer.

### Claim 11 (depends on 1)

A magnetic field sensor comprising:
a substrate extending substantially in a plane called the “plane of the substrate”,
at least one permanent magnet movable in relation to the substrate in response to a variation in the amplitude or the direction of a magnetic field to be measured,
a transducer secured to the substrate, able to convert a movement of the permanent magnet into an electrical quantity representative of the amplitude or the direction of a magnetic field to be measured,
wherein the permanent magnet is consistent with claim 1.

### Claim 12

A method of fabrication of a permanent magnet said method involving comprising:
a) forming a stack comprising N patterns stacked one upon the other in a stack direction, where N is a whole number greater than or equal to two, each pattern comprising:
a bottom antiferromagnetic layer,
a top antiferromagnetic layer, and
a ferromagnetic layer situated between the bottom and top antiferromagnetic layers,
b) heating the stack so as to achieve a temperature greater than a temperature of ordering of the material of the magnetic layers of the stack,
c) when the temperature is greater than the temperature of ordering, applying a first magnetic field to align the direction of magnetization of the ferromagnetic layers with a predetermined desired direction,
d) cooling the stack in the presence of a second magnetic field less than the first magnetic field to cause an exchange coupling to appear between the ferromagnetic layer and the bottom or top antiferromagnetic layer of said pattern of the stack,
wherein step a) comprises forming, at least once per group of ten consecutive ferromagnetic layers whose directions of magnetization are frozen by exchange coupling, a growth layer interposed between the top antiferromagnetic layer of the previous pattern and the bottom antiferromagnetic layer of the following pattern in the stack direction,
said growth layer being directly in contact with said two top and bottom antiferromagnetic layers between which it is interposed,
said growth layer being entirely realized in a nonmagnetic material chosen from the group made up of the following metals: Ta, Cu, Ru, V, Mo, Hf, Mg, NiCr and NiFeCr, or realized by a stack of several sublayers of nonmagnetic material disposed immediately on one another in the stack direction, at least one of said sublayers, known as the “metallic sublayer”, being entirely realized in a material chosen from said group, and
the thickness of the growth layer being greater than 0.5 nm.