Effect of support on structural and magnetic properties of thin FeRh/MgO films

M. JULIA JIMÉNEZ; GABRIELA F. CABEZA

Santa Fe

Conferencia; VI San Luis Conference; 2018

INCAPE-UNL

Theiron-rhodium (FeRh) alloy is known to have a first-order magnetic transitionfrom the antiferromagnetic (AFM) to the ferromagnetic (FM) state as thetemperature is increased to around 50 or 60 K above room temperature1.This alloy is of technological interest for the manufacture of new devices formagnetic storage2.Experimentally,FeRh films are deposited on substrates like MgO, Al2O3,sapphire or silicon. At present, it has been observed that FeRh films grownonto c-axis sapphire exhibits a lower transition temperature than the one grownonto MgO since tensile in-plane strain favors the FM over the AFM state3.Another important experimental result is that the AFM phase becomesincreasingly unstable as the thickness of the film decreases4. Obviously both type of substrate and the thickness of thefilm are very important parameters to take into account. In this work, we investigate the effect of thesupport (MgO) in the structural and magnetic properties of FeRh thin films byperforming density functional theory (DFT) electronic structure calculationsusing the VASP5code. Both systems have been modeled using supercells. In the case of isolatedfilms, the slab consists of 5 monolayers (ML) of FeRh with each monolayerconsisting of Fe or Rh atoms depending on whether the surface terminates in Feor Rh. In the case of the film supported on the top of a MgO slab, a substrateconsisting of 3 ML of MgO and the same number of layers of FeRh was considered.The analysis of the results shows that the supported Rh-terminated surfacesundergo greater relaxations/contractions than the Fe-terminated ones. Comparingboth Fe- and Rh- terminations for isolated and supported films theFe-terminated system is slightly more stable than the same terminated in Rh inall cases. Finally, the effect of the support on the magnetic moment (mm) ofthe atoms can be mentioned. In the case of the Rh-terminated surface, the mm ofthe all Rh atoms decrease unlike those of the Fe that increase. On the otherhand, when the Fe-terminated surfaces are considerer, all mm are increasedexcept for the Fe atoms in contact with the substrate, observing an increase inthe average magnetization of the MgO. References1.       Ostler, T. A., et. al. ?Modelingthe thickness of the magnetic phase transition temperature in thin FeRh films?,Phys. Rev. B 95, 064415/7, 2017.2.       Martí, X., et. al. ?Roomtemperature antiferromagnetic memory resistor?, Nat. Mat. Vol. 13, 367-374, 2014.3.       Gu, R. Y., et. al.?Dominance of the spin wave contribution to the magnetic phase transition inFeRh?, Phys. Rev. B 72, 012403/4,2005.4.       Han, G. C., et. al.?Magnetic stability of ultrathin FeRh films?, J. Appl. Phys. 113, 17C107/3, 2013.5.       Kresse, G., Hafner, J. ?Abinitio molecular dynamics for liquid metals?, Phys. Rev. B 47, 558-561R, 1993.