Polymorph Engineering of the Layered Rare-Earth Magnet GdAlGe

Abstract

The recent advances in research on layered magnets have established them as invaluable materials for spintronic applications and precursors to 2D magnets. The problem is that the number of such materials available for experimentation is still low. To tackle the problem, one may employ phase engineering; in particular, the interplay between the phase stability and dimensionality provides great opportunities for design of layered magnets. Here, this interrelation is harnessed to produce epitaxial films of an overlooked layered polymorph of GdAlGe. The compound is formed by alternating triangular Gd and honeycomb AlGe lattices. It is stable in ultrathin films, up to 5 monolayers. In thicker films, an additional unwanted phase emerges. The structural quality of the ultrathin films is witnessed by electron and X-ray diffraction as well as electron microscopy. Magnetization measurements detect an anisotropic ferromagnetic state. The GdAlGe magnetism is corroborated by a study of electron transport revealing the anomalous Hall effect and negative magnetoresistance. The material is naturally integrated with Ge, a technological semiconductor, which should facilitate applications. The present study can serve as a blueprint for design of layered magnets via polymorph engineering.