Nano-magnetic Multilayers in CeSb. Synchrotron Studies of Magneto-optic Materials

Kazimierz Gofron

Magneto-optic (MO) materials are currently used in data storage. Of particular interest are materials with a large Kerr effect, a rotation of the plane of polarization of incident linearly polarized light. Reported here is a structural study of CeSb, a material with the largest known MO effect (of 90 degrees).

Self-forming magnetic structures

Spontaneously forming nano-magnetic structures are examined by synchrotron diffraction studies. The magnetic planar structures consist of atomic thickness ferromagnetic and paramagnetic Ce planes forming a nano-magnetic finite multilayer. Different combinations of the ferro- and para-magnetic planes are formed at different temperatures and magnetic fields, with thickness of each nano-magnetic multilayer ranging from 1-20 nm. The nano-magnetic multilayer structure periodically repeats throughout the crystal. Without external field the Anti-Ferro Paramagnetic (AFP) structures consist of anti-ferromagnetic planes with some paramagnetic planes.

In order to better understand the formation of nano-magnetic multilayers, the studies centered on crystallographic structure changes as a function of temperature and magnetic field. For instance, below the T_N (Neel temperature), the crystallographic structure changes from the cubic to tetragonal, due to the presence of paramagnetic planes of Ce atoms in addition to ferromagnetic Ce planes. During that transition, the c axis shrinks significantly more than the a/b axis. In figures 1 and 2 we show structural change by studying the 400 charge reflection.

Below T_N the charge peak splits into two due to tetragonal distortion. The c axes shrinks more (higher h value peak) than the a/b axes. The magnetic phases have a relatively constant lattice constant with abrupt changes at the transition temperature. With the closed cycle refrigerator, we were able to reach four of the six APF phases.

Figure1: The cubic structure of CeSb undergoes tetragonal splitting below T_N as seen in 400 reflection. The c axes shrinks more than a/b axes.

Figure2: The AFP magnetic phases (multilayers) in CeSb have fixed lattice constant.