Magnetic force microscopy characterization of unusual magnetic coupling in an extraordinarily responsive magnetic material

Gd₅(Si₂Ge₂) and related compounds with similar (nearly equal Si-to-Ge ratio) composition exhibit large magnetoresponsive properties including a giant magnetocaloric effect, colossal magnetostriction, and giant magnetoresistance near a structural-magnetic phase transition that occurs close to ambient temperature. Magnetic force microscopy (MFM) and vibrating sample magnetometry (VSM) measurements on single-crystal samples of these materials indicate that the easy magnetization axis is the b-axis of the orthorhombic magnetic phase-perpendicular to the slabs. In fact, the MFM image of a surface perpendicular to the b-axis is quite similar to domain patterns perpendicular to the easy axis of Co and other highly anisotropic magnetic materials. Therefore, it appears that Gd₅(Si_xGe_1-x)₄ may require modeling similar to other multilayers and superlattices of rare-earth metals with one or more nonmagnetic constituents that exhibit long-range magnetic order across nonmagnetic layers. Many of the important phenomena of these Gd compounds could be explained by the interaction of localized Gd magnetic moments across the covalent bonding between atomic slabs, adapting models already suggested for other similar materials.