Study shows the critical point of zero anisotropy can be achieved in a wide range of film thicknesses

Magnetic anisotropy plays an important role in spintronics by defining specific directions for spins in magnetic nanostructures. Switching spins among those directions, either magnetic field or spin torque, forms the core of magnetic information storage and processing.

For practical devices, the magnetic anisotropy must not be too weak, which would allow thermal fluctuations to overwhelm the stored information, nor too strong, which would hinder spin directional switching by the magnetic field and spin torque. In order to balance these factors, it is critical to achieve a tunability of the magnetic anisotropy in a wide thickness range.

In their article, Gao et al., investigate single crystalline Ag/Fe/Fe_0.5Co_0.5/MgO(001) films grown by molecular beam epitaxy, a process widely used in the manufacture of high-quality single crystalline devices, and they then investigated the films using the magneto-optic Kerr effect.

For such a Fe/Fe_0.5Co_0.5 bilayer combination, the preferred spin axis can be tuned by varying the film thicknesses of Fe and Fe_0.5Co_0.5 over a wide range. The authors also report achieving the critical point of zero anisotropy in a wide range of thicknesses. The anisotropy in such systems is fourfold, meaning that the spin axis can have four equivalent favored directions.

The tuning of this type of anisotropy in the thickness range of practical devices will be useful in future spintronic applications if the fourfold anisotropy is utilized to carry information. This might allow for a magnetic memory design using the fourfold anisotropy to double the memory capacity compared to the binary state approach taken for today’s memory devices.

Source: “Tuning magnetic anisotropy of epitaxial Ag/Fe/Fe_0.5Co_0.5/MgO(001) films,” by N. Gao, C. Ge, Q. Li, M. Yang, C. Hwang, and Z. Q. Qiu, Journal of Applied Physic (2018). The article can be accessed at https://doi.org/10.1063/1.5052297 .