Coercivity enhancement in Ni/VOₓ bilayers due to interfacial strain coupling
Thomas Saerbeck (Dept. of Physics and Center for Advanced Nanoscience, Univ. of California San Diego)

Heterostructures of dissimilar materials offer a unique possibility to tailer and control magnetic properties without the aid of external magnetic fields. In my talk I will present interfacial strain coupling as a tool to effectively tune magnetic properties of a ferromagnetic film in a flexible and reversible manner. Effective control over magnetic coercivity and magnetization in a vanadium-oxide/ferromagnet hybrid structure is achieved. Magnitude of the changes and temperature window are set by the choice of the materials and structure.
The oxides V₂O₃ and VO₂ undergo a metal-to-insulator transition concurrent with a structural phase transition at 165 K and 340 K, respectively. The structural deformation of the interface causes stress anisotropy in the magnetic film and therefore alters the magnetic properties [1,2]. A change in coercivity by a factor of two is observed reversibly in temperature with the thermal hysteresis of the first-order phase transition of the oxide. In addition, a length scale competition between magnetic and structural domains leads to coercivity enhancements of 300 % in the center of the transition. This maximum enhancement is related to a phase coexistence of metallic and insulating domains in the oxide.
The magnetism aspects of this work were supported by the Office of Basic Energy Science, U.S. Department of Energy, under Grant No. DE FG03-87ER-45332 and the oxide related science by the AFOSR Grant No. FA9550-12-1-0381.

[1] J. de la Venta, S. Wang, J. G. Ramirez, and I. K. Schuller, Appl. Phys. Lett. 102, 122404 (2013).

[2] J. de la Venta, S. Wang, T. Saerbeck, J. G. Ramirez, I. Valmianski, and I. K. Schuller, Appl. Phys. Lett. 104, 062410 (2014).