AVS 55th International Symposium & Exhibition
    Magnetic Interfaces and Nanostructures Thursday Sessions
       Session MI-ThM

Paper MI-ThM10
Phase Coexistence in the AF to FM Transition in Epitaxial FeRh Thin Films

Thursday, October 23, 2008, 11:00 am, Room 206

Session: Magnetic Surfaces, Interfaces, Thin Films and Heterostructures
Presenter: Y. Ding, Brookhaven National Laboratory
Authors: D.A. Arena, Brookhaven National Laboratory
Y. Ding, Brookhaven National Laboratory
L.H. Lewis, Northeastern University
C.J. Kinane, University of Leeds, UK
B.J. Hickey, University of Leeds, UK
C.H. Marrows, University of Leeds, UK
J.-W. Kim, Argonne National Laboratory & Ames Laboratory
P.J. Ryan, Argonne National Laboratory & Ames Laboratory
M. Ali, University of Leeds, UK
Correspondent: Click to Email

The near equiatomic, ordered alloy FeRh exhibits an unusual first order antiferromagnetic (AF) to ferromagnetic (FM) phase transition at around 380 K1 and interest in this system has increased recently, driven both from unresolved scientific questions and potential applications in high-density storage media and advanced sensors. In these studies, highly ordered, epitaxial thin films of FeRh, grown by molecular beam epitaxy (MBE), were measured with a variety of techniques including using x-ray magnetic circular dichroism (XMCD), and conventional and surface x-ray diffraction (XRD). XMCD was measured in two modes: surface sensitive total electron yield (TEY) and bulk sensitive indirect transmission (IT). The TEY data reveal a persistence of ferromagnetism in the near surface region at room temperature while the indirect transmission data indicate that the bulk material is not FM ordered and is presumably AF. In general terms, conventional XRD measurements from our thin films show that the AF to FM phase transition, which is hysteretic in temperature, is accompanied by an abrupt lattice expansion; this behavior mirrors the expansion observed in bulk samples. However, high-resolution XRD data indicate that the lattice expansion is not smooth, but rather occurs via the coexistence of two distinct lattice parameters, where the smaller volume lattice is presumably associated with the AF phase and the larger lattice contains the FM ordered FeRh. Surface XRD, acquired near the critical angle for x-ray penetration, reveals that the temperature for the transition from the smaller to the larger lattice parameter occurs at a reduced temperature for the surface than for the bulk. Comparisons with the XMCD data for different capping layers of the FeRh films and sum-rule analyses of the Fe magnetic moment will also be discussed.

1J. S. Kouvel and C. C. Hartelius, J. Appl. Phys. 33, 1343 (1962).