Pattern writing of magnetic order using ion irradiation of a magnetic phase transitional thin film

1. An article comprising:

a substrate; and

a layer of an FeRh alloy disposed on the substrate;

wherein the alloy comprises:

a continuous antiferromagnetic phase; and

one or more discrete phases smaller in area than the continuous phase having a lower metamagnetic transition temperature than the continuous phase;

wherein the one or more discrete phase has a superparamagnetic limit that exceeds the superparamagnetic limit of the continuous phase.

2. The article of claim 1 , wherein the alloy comprises an array of the discrete phases.

3. The article of claim 1 , wherein the discrete phase is ferromagnetic.

4. A method comprising:

providing an article comprising:

a substrate; and a layer of an FeRh alloy disposed on the substrate; wherein the alloy comprises: a continuous antiferromagnetic phase; and one or more discrete phases smaller in area than the continuous phase having a lower metamagnetic transition temperature than the continuous phase; wherein the one or more discrete phase has a superparamagnetic limit that exceeds the superparamagnetic limit of the continuous phase; wherein the discrete phase is ferromagnetic; and

orienting the magnetic polarization of a first ferromagnetic discrete phase.

5. The method of claim 4 , further comprising:

orienting the magnetic polarization of a second ferromagnetic discrete phase in a direction different from that of the first ferromagnetic discrete phase.

6. A method comprising:

providing an article comprising:

a substrate; and a layer of an FeRh alloy disposed on the substrate; wherein the alloy comprises: a continuous antiferromagnetic phase; and one or more discrete phases smaller in area than the continuous phase having a lower metamagnetic transition temperature than the continuous phase; wherein the one or more discrete phase has a superparamagnetic limit that exceeds the superparamagnetic limit of the continuous phase; wherein the discrete phase is ferromagnetic; and

determining the orientation of the magnetic polarization of the ferromagnetic discrete phase.

7. The article of claim 1 , wherein the area of the discrete phase is no more than 1000 μm 2 .

8. The article of claim 1 , wherein the area of the discrete phase is no more than 1000 nm 2 .

9. The article of claim 1 , wherein the discrete phase has a metamagnetic transition temperature of 20° C. to 140° C.

10. A method comprising:

providing an article comprising:

a substrate; and a layer of an FeRh alloy disposed on the substrate; wherein the alloy comprises: a continuous antiferromagnetic phase; and one or more discrete phases smaller in area than the continuous phase having a lower metamagnetic transition temperature than the continuous phase; wherein the one or more discrete phase has a superparamagnetic limit that exceeds the superparamagnetic limit of the continuous phase; and

detecting the presence, absence, or location of any ferromagnetic discrete phases.

11. The method claim 10 , further comprising:

adjusting the temperature of the article before the detection.

12. The article of claim 1 , wherein at least two of the discrete phases have different metamagnetic temperatures.

13. A method comprising:

providing an article comprising:

a substrate; and a layer of an FeRh alloy disposed on the substrate; wherein the alloy comprises: a continuous antiferromagnetic phase; and one or more discrete phases smaller in area than the continuous phase having a lower metamagnetic transition temperature than the continuous phase; wherein the one or more discrete phase has a superparamagnetic limit that exceeds the superparamagnetic limit of the continuous phase; wherein at least two of the discrete phases have different metamagnetic temperatures; and

detecting the presence, absence, or location of any ferromagnetic discrete phases;

adjusting the temperature of the article; and

detecting the presence, absence or location of any ferromagnetic discrete phases.

14. The article of claim 1 , wherein the discrete phases have a size and pitch that exceed the superparamagnetic limit of the continuous phase.

15. The article of claim 1 , wherein the substrate comprises MgO.

16. The article of claim 1 , wherein the substrate comprises a piezoelectric material.

17. A method comprising:

providing an article comprising:

a substrate; and a layer of an FeRh alloy disposed on the substrate; wherein the alloy comprises: a continuous antiferromagnetic phase; and one or more discrete phases smaller in area than the continuous phase having a lower metamagnetic transition temperature than the continuous phase; wherein the one or more discrete phase has a superparamagnetic limit that exceeds the superparamagnetic limit of the continuous phase; wherein the substrate comprises a piezoelectric material; and

applying a voltage to the piezoelectric material that alters the metamagnetic temperature of one or more of the discrete phases; and detecting the presence, absence, or location of any ferromagnetic discrete phases.

18. A method comprising:

providing an article comprising:

a substrate; and

a layer comprising a continuous phase of an antiferromagnetic FeRh alloy disposed on the substrate; and

directing an ion source at one or more portions of the alloy to create one or more discrete phases smaller in area than the continuous phase having a lower metamagnetic transition temperature than the continuous phase;

wherein the one or more discrete phases has a superparamagnetic limit that exceeds the superparamagnetic limit of the continuous phase.

19. The method of claim 18 , wherein the ion source produces He + ions.

20. The method of claim 18 , wherein a mask is used to define the discrete phases.

21. The method of claim 18 , wherein the ion source is a beam.

22. The method of claim 18 , wherein the ion source is a He + beam having a diameter of no more than 5 nm.

23. The method of claim 18 , wherein the dose of the ion source is adjusted to create at least two discrete phases having different metamagnetic transition temperatures.

24. A method comprising:

providing an article comprising:

a substrate; and

a layer comprising a continuous phase of an antiferromagnetic FeRh alloy disposed on the substrate; and

directing an electron source at one or more portions of the alloy to create one or more discrete phases smaller in area than the continuous phase having a lower metamagnetic transition temperature than the continuous phase;

wherein the one or more discrete phases has a superparamagnetic limit that exceeds the superparamagnetic limit of the continuous phase.

25. The method of claim 24 , wherein the electron source produces electrons with kinetic energy between 300 keV and 460 keV.

26. The method of claim 24 , wherein the electron source produces electrons with kinetic energy above 460 keV.

27. The method of claim 24 , wherein a mask is used to define the discrete phases.

28. The method of claim 24 , wherein the electron source is a beam.

29. The method of claim 24 , wherein the electron source is an electron beam having a diameter of no more than 5 nm.

30. The method of claim 24 , wherein the dose of the electron source is adjusted to create at least two discrete phases having different metamagnetic transition temperatures.

31. The method of claim 24 , wherein the energy of the electron source is adjusted to preferentially create Fe vacancies.

32. The method of claim 25 , wherein the energy of the electron source is adjusted to create both Fe and Rh vacancies.

33. The article of claim 1 , wherein the area of the discrete phase is no more than 25 nm×25 nm.