B. J. Ruck

Epitaxial growth of (100)-oriented rare-earth nitrides (RENs) SmN, GdN, and DyN on (100)LaAlO3 (LAO) substrates is demonstrated using molecular beam epitaxy. RHEED and ϕ-scans confirm that the cubic RENs grow 45° rotated with respect to the pseudocubic (100)-surface of LAO, which leads to lattice mismatches between −5.8% and −8.7% for the selected RENs. Those lattice mismatches, despite being significant, are smaller than in previously reported epitaxial (100)RENs, with the exception of growth on (100)YSZ (yttria stabilized zirconia), which however causes the formation of an interface oxide layer. The SmN RHEED pattern shows intense streaks, indicating a high quality, flat surface, and the rocking curves are among the narrowest reported for (100)RENs. In contrast to growth on Si, the epitaxial RENs readily form over a wide range of substrate temperatures, without the need of special substrate treatment or intermediate layers. This robust, high quality growth paired with their clear magnetic switching behavior makes epitaxial RENs grown on LAO ideal candidates for future spintronic devices.

We demonstrate a nonvolatile cryogenic magnetic memory element needed to support emerging superconducting- and quantum-computing technologies. The central element is a switchable tri-layer thin film magnetic dot comprising two semiconducting ferromagnetic GdxSm1−xN layers separated by an exchange-blocking Al layer. The materials are explored for their tunable magnetic responses, the potential to engineer compensating magnetic moments in the anti-parallel tri-layers. The stability of the parallel and anti-parallel states and the reproducibility over repeated cycles are also demonstrated. We show that the tri-layer stacks can be formed into dots as small as 4 μm diameter, without affecting their magnetic behavior.

A unique bulk-origin perpendicular magnetic anisotropy (PMA) is reported in thin films of the cubic ferromagnetic semiconductor GdxSm1−xN. PMA behavior is clearly signaled by in-vs-out-of-plane magnetic hysteresis showing out-of-plane remanence of ∼80% of the saturation magnetization in films with up to 30% Gd. Anomalous Hall effect data show further that the conduction-band spin imbalance shows complete 100% remanence to retain half-metallic conduction even as the out-of-plane applied field is reduced to zero, in stark contrast to the 80% magnetization remanence. The unusual occurrence of PMA in this cubic material is discussed as stabilized by a mix of two in-plane crystal orientations in the epitaxial (111)-oriented films.