Strategies to perform magnetization reversals in ferromagnets

Patent metadata

Field	Value
Publication number	US-11621111-B2
Application number	US-202117483405-A
Country	US
Kind code	B2
Filing date	Sep 23, 2021
Priority date	Sep 23, 2020
Publication date	Apr 4, 2023
Grant date	Apr 4, 2023

Abstract

Systems and methods for reversing a magnetization in a ferromagnet include a nanometer-scale cylindrical ferromagnetic sample having a height to diameter aspect ratio on the order of 2 or greater. A temporally-varying external field comprising an r.f. Pi pulse is applied to the ferromagnetic sample to cause a precession magnetization vector inclined at an angle with respect to the longest axis of the ferromagnetic sample to continuously rotate around the longest axis. One or more parameters of the temporally-varying external field is continuously adjusted based on at least magnetization dynamics of the ferromagnetic sample and/or an angular dependence of a precession frequency of the ferromagnetic sample.

First claim

What is claimed is:

1. A method for performing magnetization reversals in ferromagnets, the method comprising:
providing a cylindrical ferromagnetic sample having a height dimension along a z-axis that is larger than a diameter dimension in an x-y plane that is perpendicular to the z-axis, the x-y plane defined by an x-axis that is perpendicular to the z-axis and a y-axis that is perpendicular to both the z-axis and the x-axis;
applying a temporally-varying external field comprising a chirped r.f. Pi pulse to the ferromagnetic sample along a direction perpendicular to the z-axis in the x-y plane, an x-axis component and a y-axis component of the temporally-varying external field each having a magnitude that temporally varies according to a different function of time to cause the temporally-varying external field to continuously rotate a precession magnetization vector around the z-axis, the precession magnetization vector being inclined at an angle with respect to the z-axis; and
sweeping a frequency of the chirped r.f. Pi pulse based on an instantaneous precession frequency and a corresponding angle of inclination of the precession magnetization vector.

2. The method of claim 1 , further comprising applying a static non-zero external field to the ferromagnetic sample along a direction of the z-axis.

3. The method of claim 1 , further comprising applying a static non-zero external field having a magnitude of at least 2000 Oe to the ferromagnetic sample along a direction of the z-axis.

4. The method of claim 1 , further comprising adjusting operational parameters for chirping the r.f. pulse applied to the ferromagnetic sample based on an angular dependence of the precession frequency.

5. The method of claim 1 , wherein providing the ferromagnetic sample comprises providing a ferromagnetic sample having a height dimension along a z-axis that is 150 nm or less and that is at least twice the diameter dimension in the x-y plane.

6. The method of claim 1 , wherein providing the ferromagnetic sample comprises providing a ferromagnetic sample having a height dimension along a z-axis that is 50 nm or less and that is at least twice the diameter dimension in the x-y plane.

7. The method of claim 1 , wherein providing the ferromagnetic sample comprises providing an yttrium iron garnet (YIG) sample having uniaxial shape anisotropy.

8. The method of claim 1 , wherein applying an external field comprising a chirped r.f. Pi pulse comprises applying a circularly polarized field.

9. The method of claim 1 , wherein the applied external field comprising the chirped r.f. Pi pulse has a magnitude of at least 200 Oe.

10. A method for performing magnetization reversals in ferromagnets, the method comprising:
providing a cylindrical ferromagnetic sample having a height dimension along a z-axis that is larger than a diameter dimension in an x-y plane that is perpendicular to the z-axis, the x-y plane defined by an x-axis that is perpendicular to the z-axis and a y-axis that is perpendicular to both the z-axis and the x-axis;
applying a temporally-varying external field comprising a constant-frequency r.f. Pi pulse to the ferromagnetic sample along a direction perpendicular to the z-axis in the x-y plane, an x-axis component and a y-axis component of the temporally-varying external field each having a magnitude that temporally varies according to a different function of time to cause the temporally-varying external field to continuously rotate a precession magnetization vector around the z-axis, the precession magnetization vector being inclined at an angle with respect to the z-axis;
applying a temporally-varying external field comprising a temporally-varying magnitude of a z-axis component to the ferromagnetic sample along a direction of the z-axis; and
sweeping a magnitude of the constant-frequency r.f. Pi pulse based on an instantaneous precession frequency and a corresponding angle of inclination of the precession magnetization vector.

11. The method of claim 10 , wherein applying the temporally-varying external field along a direction perpendicular to the z-axis in the x-y plane comprises applying a circularly polarized field.

12. The method of claim 10 , wherein applying the temporally-varying external field along a direction perpendicular to the z-axis in the x-y plane comprises applying a linearly polarized field.

13. The method of claim 10 , further comprising adjusting operational parameters for at least one of the temporally-varying external fields along the z-axis or the x-y plane applied to the ferromagnetic sample based on an angular dependence of the precession frequency.

14. The method of claim 10 , wherein providing the ferromagnetic sample comprises providing a ferromagnetic sample having a height dimension along a z-axis that is 150 nm or less and that is at least twice the diameter dimension in the x-y plane.

15. The method of claim 10 , wherein providing the ferromagnetic sample comprises providing a ferromagnetic sample having a height dimension along a z-axis that is 50 nm or less and that is at least twice the diameter dimension in the x-y plane.

16. The method of claim 10 , wherein providing the ferromagnetic sample comprises providing an yttrium iron garnet (YIG) sample having uniaxial shape anisotropy.

17. The method of claim 10 , wherein the applied external field comprising the r.f. Pi pulse has a magnitude of at least 200 Oe.

18. A system for reversing a magnetization in a ferromagnet, the system comprising:
a cylindrical ferromagnetic sample having a height dimension along a z-axis that is larger than a diameter dimension in an x-y plane that is perpendicular to the z-axis, where the x-y plane is defined by an x-axis that is perpendicular to the z-axis and a y-axis that is perpendicular to both the z-axis and the x-axis;
a first magnetic field generator is configured to apply a temporally-varying external field comprising an r.f. Pi pulse to the ferromagnetic sample along a direction perpendicular to the z-axis in the x-y plane, an x-axis component and a y-axis component of the temporally-varying external field each having a magnitude that temporally varies according to a different function of time to cause the temporally-varying external field to continuously rotate a precession magnetization vector around the z-axis, the precession magnetization vector being inclined at an angle with respect to the z-axis; and
a computer configured to control the magnetic field generator to continuously vary one or more parameters of the temporally-varying external field comprising an r.f. Pi pulse to the ferromagnetic sample along a direction perpendicular to the z-axis in the x-y plane, based on an angular dependence of a precession frequency of the ferromagnetic sample.

19. The system of claim 18 , further comprising:
a second magnetic field generator configured to apply one or more of a static external field or a temporally-varying external field comprising to the ferromagnetic sample along the z-axis and perpendicular to the x-y plane.

20. The system of claim 18 , further comprising:
a sensor for measuring magnetization dynamics of the ferromagnetic sample;
wherein the computer controls the magnetic field generator based on measurement data received from the sensor.

Assignees

• Univ Northwestern

Inventors

• Ketterson John B
• Garg Anupam K
• Lim Jinho
• Zhang Zhaohui

Classifications

• H01F13/006 Primary

  Methods and devices for demagnetising of magnetic bodies, e.g. workpieces, sheet material (for erasing of information on magnetic record carriers G11B5/00) · CPC title

• G01R33/20

  involving magnetic resonance (medical aspects A61B5/055; magnetic resonance gyrometers G01C19/60) · CPC title

• H01F13/00 Primary

  Apparatus or processes for magnetising or demagnetising ({devices for holding workpieces using magnetic or electric force acting directly on the workpieces B23Q3/15} ; for degaussing ships B63G9/06; for clocks or watches G04D9/00; {recording or erasing of information on magnetic record carriers G11B5/00} ; demagnetising arrangements for colour television H04N9/29) · CPC title