Voltage-controlled magnetic device operating over a wide temperature range

Patent metadata

Field	Value
Publication number	US-9508920-B2
Application number	US-201414906770-A
Country	US
Kind code	B2
Filing date	Jul 18, 2014
Priority date	Jul 22, 2013
Publication date	Nov 29, 2016
Grant date	Nov 29, 2016

Abstract

A voltage-controlled spintronic device includes a magnetic layer having an effective anisotropy Keff; a non-magnetic insulating layer; a contact layer; the magnetic layer having an anisotropy switching threshold such that application of a polarization voltage Vmax allows switching of the effective anisotropy K eff from a direction perpendicular to the reference plane to a direction in the reference plane or vice versa, the magnetic layer including a first layer, with thickness t B , having a volume anisotropy K VB ; a second layer, with thickness t A , having a surface anisotropy K SA and a volume anisotropy K VA ; the surface anisotropy K SA and the volume anisotropies K VA and K VB respecting, over a given operating temperature range: Min(K SA (V=0), K SA (V=Vmax))<−{K VB t B +K VA t A )<Max(K SA (V=0), K SA (V=Vmax)). K SA (V=0) is the surface anisotropy when no polarization voltage is applied. K SA (V=Vmax) is the surface anisotropy when a polarization voltage V max is applied.

First claim

The invention claimed is:

1. A voltage-controlled magnetic device comprising:
a magnetic layer extending along a reference plane and having a variable direction magnetisation and an effective anisotropy K eff ;
a non-magnetic insulating layer extending onto the magnetic layer;
a contact layer extending onto the non-magnetic insulating layer;
a polarisation voltage device configured to apply a polarisation voltage between the contact layer and the magnetic layer, through the non-magnetic insulating layer;
said magnetic layer having an anisotropy switching threshold such that the application of a polarisation voltage V max through the non-magnetic insulating layer enables switching of the effective anisotropy K err from a direction perpendicular to the reference plane to a direction in the reference plane or vice versa,
wherein the magnetic layer comprises:
a first layer with thickness t B , having a first volume anisotropy K VB ;
a second layer with thickness t A , having a surface anisotropy K SA and a second volume anisotropy K VA , the second layer being situated between the first layer and the non-magnetic insulating layer;
a composition and a thickness of the second and first layers being chosen in order that the surface anisotropy K SA and the first and second volume anisotropies K VB and K VA respect, over a given operating temperature range, the following inequality:
Min=( K SA ( V= 0), K SA ( V=V max ))<− K VB t B +K VA t A )<Max( K SA ( V= 0), K SA ( V=V max ))

 where K SA (V=0) is the surface anisotropy when no polarisation voltage is applied; K SA (V=V max ) is the surface anisotropy when the polarisation voltage V max is applied.

2. The magnetic device according to claim 1 , wherein the non-magnetic insulating layer is made of MgO, AlOx, AlN, SrTiO 3 , HfO x or any other insulating oxide or nitride having a dielectric polarisability greater than or equal to 6.

3. The magnetic device according to claim 1 , wherein
the effective anisotropy K eff is in a direction perpendicular to the reference plane when no polarisation voltage is applied;
the effective anisotropy K eff is in a direction in the reference plane when the polarisation voltage V max is applied.

4. The magnetic device according to claim 3 , wherein
the surface anisotropy K SA of the second layer is in a direction perpendicular to the reference plane and the surface anisotropy K SA decreases when the polarisation voltage V max is applied;
the total volume anisotropy K VB t B +K VA t A is in a direction in the reference plane.

5. The magnetic device according to claim 3 , wherein
the surface anisotropy K SA of the second layer is in a direction in the reference plane and the surface anisotropy K SA increases when the polarisation voltage V max is applied;
the total volume anisotropy K VB t B +K VA t A is in a direction perpendicular to the reference plane.

6. The magnetic device according to claim 1 , wherein
the effective anisotropy K eff is in a direction in the reference plane when no polarisation voltage is applied;
the effective anisotropy K eff is in a direction perpendicular to the reference plane when the polarisation voltage V max is applied.

7. The magnetic device according to claim 6 , wherein
the surface anisotropy K SA of the second layer is in a direction perpendicular to the reference plane and the surface anisotropy K SA increases when the polarisation voltage V max is applied;
the total volume anisotropy K VB t B +K VA t A is in a direction in the reference plane.

8. The magnetic device according to claim 6 , wherein
the surface anisotropy K SA of the second layer is in a direction in the reference plane and the surface anisotropy K SA decreases when the polarisation voltage V max is applied;
the total volume anisotropy K VB t B +K VA t A is in a direction perpendicular to the reference plane.

9. The magnetic device according to claim 1 , wherein the second layer is made of an alloy based on Co, Fe, Ni or any other material leading, in combination with the insulating layer, to a surface anisotropy K SA perpendicular to the reference plane and having a variation greater than 5% as a function of the application or not of the polarisation voltage V max .

10. The magnetic device according to claim 1 , wherein the first layer having the first volume anisotropy K VB is a multilayer stack of n elementary patterns of type F1/N1 or F1/N1/F2/N2 or F1/F2, with F1 and F2 two different ferromagnetic materials and N1 and N2 two different non-magnetic materials.

11. The magnetic device according to claim 1 , wherein the first layer having the first volume anisotropy K VB is an alloy having a tetragonal structure L1 0 .

12. The magnetic device according to claim 1 , wherein the first layer having the first volume anisotropy K VB is a monolayer of an alloy of type F1F2F3N1N2, with F1, F2 and F3 three different ferromagnetic materials and N1 and N2 two different non-magnetic materials.

13. The magnetic device according to claim 1 , wherein
the contact layer comprises, in contact with the non-magnetic insulating layer, a magnetic layer having a fixed magnetisation direction serving as reference direction for the magnetisation;
the non-magnetic insulating layer is a tunnel barrier enabling a current to circulate by tunnel effect between the contact layer and the magnetic layer;
the device then behaving like a magnetic tunnel junction.

14. The magnetic device according to claim 13 , wherein
the magnetic layer of the contact layer is an alloy of CoFeB;
the non-magnetic insulating layer is made of MgO;
the second layer of the magnetic layer is an alloy of CoFeB.

Assignees

• Commissariat á l'énergie atomique et aux énergies alternatives
• Centre Nat De La Rech Scient (Crns)
• Commissariat L Energie Atomique Et Aux Energies Alternatives
• Centre Nat De La Rech Scient (Cnrs)
• Université Joseph Fourier

Inventors

• Dieny Bernard
• Bea Hélène
• Bandiera Sébastien

Classifications

• G01R33/093

  using multilayer structures, e.g. giant magnetoresistance sensors (thin magnetic films H01F10/00) · CPC title

• H01F10/3254

  the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ] · CPC title

• H01F10/329

  Spin-exchange coupled multilayers wherein the magnetisation of the free layer is switched by a spin-polarised current, e.g. spin torque effect · CPC title

• G01R33/1284

  Spin resolved measurements; Influencing spins during measurements, e.g. in spintronics devices · CPC title

• G11C11/161

  details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell · CPC title