Magnetoelectric control of superparamagnetism

Patent metadata

Field	Value
Publication number	US-9355764-B2
Application number	US-201414155283-A
Country	US
Kind code	B2
Filing date	Jan 14, 2014
Priority date	Jan 14, 2013
Publication date	May 31, 2016
Grant date	May 31, 2016

Abstract

A magnetoelectric composite device having a free (i.e. switchable) layer of ferromagnetic nanocrystals mechanically coupled a ferroelectric single crystal substrate is presented, wherein application of an electrical field on the composite switches the magnetic state of the switchable layer from a superparamagnetic state having no overall net magnetization to a substantially single-domain ferromagnetic state.

First claim

What is claimed is:

1. A magnetoelectric device, comprising:
a superparamagnetic element; and
a dielectric element coupled to the superparamagnetic element;
wherein the superparamagnetic element is coupled to the dielectric element such that presence of an electric field switches the magnetic state of the superparamagnetic element between a superparamagnetic state and a substantially single-domain ferromagnetic state; and
wherein the superparamagnetic state comprises substantially no overall net magnetization.

2. A magnetoelectric device as recited in claim 1 , wherein the device is configured to switch the magnetic state of the superparamagnetic element at room temperature.

3. A magnetoelectric device as recited in claim 2 , wherein the electric field is used to turn on and off a permanent magnetic moment of the device.

4. A magnetoelectric device as recited in claim 2 , wherein the superparamagnetic element is mechanically coupled to the dielectric element such that the presence of the electric field induces a strain between the superparamagnetic element and the dielectric element to switch the magnetic state.

5. A magnetoelectric device as recited in claim 4 :
wherein the superparamagnetic element comprises a plurality of nanoparticles; and
wherein the dielectric element comprises a substrate comprising a ferroelectric material mechanically coupled to the nanoparticles.

6. A magnetoelectric device as recited in claim 5 , wherein the dielectric element comprises a piezoelectric substrate.

7. A magnetoelectric device as recited in claim 6 , wherein a free layer comprises Ni nanocrystals embedded within a PT layer.

8. A magnetoelectric device as recited in claim 7 , wherein the substrate comprises PMN-PT mechanically coupled to the nanocrystals.

9. A magnetoelectric device as recited in claim 4 , wherein the substrate comprises upper and lower electrodes disposed on both sides of the substrate.

10. A magnetoelectric device as recited in claim 9 :
wherein the upper electrode and the nanoparticles partially oxidize to promote adhesion; and
wherein said adhesion is configured to facilitate strain transfer between the substrate and the nanoparticles.

11. A magnetoelectric device as recited in claim 2 , wherein the superparamagnetic element comprises a material having a non-zero magnetostriction configured such that any induced magnetoelastic anisotropy causes magnetic dipoles in the superparamagnetic element to align either parallel or perpendicular to a dominant compressive strain direction.

12. A multiferroic composite, comprising:
a switchable superparamagnetic element having an electric-field-induced anisotropy; and
a ferroelectric element coupled to the superparamagnetic element;
wherein the superparamagnetic element is coupled to the ferroelectric element such that presence of an electric field switches the magnetic state of the superparamagnetic element between a superparamagnetic state and a substantially single-domain ferromagnetic state; and
wherein the superparamagnetic state comprises substantially no overall net magnetization.

13. A composite as recited in claim 12 , wherein the composite is configured to switch the magnetic state of the superparamagnetic element at room temperature.

14. A composite as recited in claim 13 , wherein the electric field is used to turn on and off a permanent magnetic moment of the composite.

15. A composite as recited in claim 13 :
wherein the superparamagnetic element comprises a first layer having a plurality of nanoparticles;
wherein the ferroelectric element comprises a piezoelectric substrate; and
wherein the superparamagnetic element is mechanically coupled to the piezoelectric substrate such that the presence of an electric field induces a strain between the superparamagnetic element and the dielectric element to switch the magnetic state.

16. A composite as recited in claim 15 , wherein the superparamagnetic element comprises Ni nanocrystals embedded within a PT layer.

17. A composite as recited in claim 16 , wherein the substrate comprises PMN-PT.

18. A composite as recited in claim 15 , wherein the substrate comprises upper and lower electrodes disposed on both sides of the substrate.

19. A composite as recited in claim 18 :
wherein the upper electrode and the nanoparticles partially oxidize to promote adhesion; and
wherein said adhesion is configured to facilitate strain transfer between the substrate and the nanoparticles.

20. A composite as recited in claim 13 , wherein the superparamagnetic element comprises a material having a non-zero magnetostriction configured such that any induced magnetoelastic anisotropy causes magnetic dipoles in the superparamagnetic element to align either parallel or perpendicular to a dominant compressive strain direction.

21. A composite as recited in claim 13 , wherein the composite is a component within a magnetic memory circuit.

Assignees

• Univ California

Inventors

• Tolbert Sarah H
• Carman Gregory P
• KELLER Scott
• Schelhas Laura
• Kim Hyungsuk
• Hockel Joshua

Classifications

• H01F1/0063 Primary

  in a non-magnetic matrix, e.g. granular solids (granular films H01F10/007) · CPC title

• H01F1/0018

  Diamagnetic or paramagnetic materials, i.e. materials with low susceptibility and no hysteresis (H01F1/0036 takes precedence) · CPC title

• H01F1/0036 Primary

  showing low dimensional magnetism, i.e. spin rearrangements due to a restriction of dimensions, e.g. showing giant magnetoresistivity, (H01F1/153, H01F1/42 and H01F10/00 take precedence; magnetoresistive sensors G01D5/16, G01R33/06; magnetoresistive recording G11B5/39; magnetic-field-controlled resistors H10N50/10) · CPC title