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Magnetism recharged: A new method for restoring magnetism in thin films

Modern low-power solutions to computer memory rely heavily on the manipulation of the magnetic properties of materials. Understanding the influence of the chemical properties of these materials on their magnetization ability is of key importance in developing the field.

A study in Applied ÌÇÐÄÊÓƵics Letters, led by researchers from SANKEN at The University of Osaka, has revealed a technique for recovering magnetism in a degraded spintronics device. This method can be applied to improve the robustness of next-generation semiconductor memory.

Spintronics exploits the spin (and charge) of electrons to process and store memory, and this is achieved practically by stacking layers of thin material films that behave differently under the influence of a magnetic field.

"These devices can be non-volatile, low-power, and robust, but the manufacturing process can cause their magnetic properties to deteriorate," explains Tomohiro Koyama, lead author of the study.

The thin films required for these devices are often formed via sputtering, in which atoms are extracted and deposited onto a substrate. This process, however, can often lead to the magnetic layer becoming oxidized, spoiling its magnetic properties.

The device investigated in this study consisted of a Co/MgO structure with underlayers formed of Pt or Au. Pt is a promising material for improving the robustness of spintronics devices, as it is strongly susceptible to catalytic action, enabling chemical reactions to proceed under milder conditions.

The researchers adjusted the oxidation damage to the Co layer by changing the sputtering power during deposition of the MgO layer. Annealing with molecular hydrogen (H₂) was then performed, and the changes in the magnetic properties of the material were observed and compared with those before annealing.

Measurements of the anomalous Hall effect are a standard method for measuring the magnetization properties of a material. The characteristic hysteresis curve associated with magnetic materials was observed only for the annealed sample, whereas the pre-treated sample exhibited only a minimal level of magnetization.

"The strong catalytic action of Pt is fundamental in allowing the recovery of the magnetic properties of Co after oxidation and could help us to inform the design of future post-silicon devices," says Tomohiro Koyama.

A similar set of measurements were performed with an Au underlayer, rather than Pt; in this case, no effect of annealing on the magnetization was observed. These results confirm that the recovery of magnetization is a result of the inclusion of the Pt layer.

The influence of catalysts on degraded thin-film magnets has been revealed by this study and can be applied to a wide range of practical devices. This innovative technique could be key in improving the robustness of next-generation semiconductor memory.