SmN is ferromagnetic below 27 K, and its net magnetic moment of 0.03 Bohr magnetons per formula unit is one of the smallest magnetisations found in any ferromagnetic material. The nearzero moment is a result of the nearly equal and opposing spin and orbital moments in the 6 H 5/2 ground state of the Sm 3+ ion, which leads finally to a nearly complete cancellation for an ion in the SmN ferromagnetic state. Here we explore the spin alignment in this compound with X-ray magnetic circular dichroism at the Sm L 2,3 edges. The spectral shapes are in qualitative agreement with computed spectra based on an LSDA+U (local spin density approximation with Hubbard-U corrections) band structure, though there remain differences in detail which we associate with the anomalous branching ratio in rare-earth L edges. The sign of the spectra determine that in a magnetic field the Sm 4f spin moment aligns antiparallel to the field; the very small residual moment in ferromagnetic SmN aligns with the 4f orbital moment and antiparallel to the spin moment. Further measurements on very thin (1.5 nm) SmN layers embedded in GdN show the opposite alignment due to a strong Gd-Sm exchange, suggesting that the SmN moment might be further reduced by about 0.5 % Gd substitution.

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We report measurements of the optical response of polycrystalline DyN thin films. The frequency-dependent complex refractive index in the near IR-visible-near UV was determined by fitting reflection/transmission spectra. In conjunction with resistivity measurements these identify

The strong spin-orbit interaction in the rare-earth elements ensures that even within a ferromagnetic state there is a substantial orbital contribution to the ferromagnetic moment, in contrast to more familiar transition metal systems, where the orbital moment is usually quenched. The orbital-dominant magnetization that is then possible within rare-earth systems facilitates the fabrication of entirely new magnetic heterostructures, and here we report a study of a particularly striking example comprising interfaces between GdN and SmN. Our investigation reveals a twisted magnetization arising from the large spin-only magnetic moment in GdN and the nearly zero, but orbital-dominant, moment of SmN. The unusual twisted phase is driven by (i) the similar ferromagnetic Gd-Gd, Sm-Sm and Gd-Sm exchange interactions, (ii) a SmN Zeeman interaction 200 times weaker than that of GdN, and (iii) the orbital-dominant SmN magnetic moment. The element specificity of X-ray magnetic circular dichroism (XMCD) is used in seperate modes probing both bulk and surface regions, revealing the depth profile of the twisting magnetization. PACS numbers: 75.25-j, 75.47.-m, 75.50.Pp 1 arXiv:1504.04425v1 [cond-mat.mtrl-sci] 17 Apr 2015 I. INTRODUCTION An inhomogeneous, twisted magnetic ordering commonly occurs near interfaces between ferromagnetic materials, due to competing interactions which favor opposing alignments of the magnetization. These phases are types of engineered domain walls, and thus have important implications for spintronics applications, where current-driven domain wall motion is an active area of research. 1-4 So far, twisted phases are known to manifest in diverse magnetic systems, 5-12 however these all fall under the conventional spin-dominant paradigm of magnetism where the orbital moment plays no significant role. Competing interactions in the presence of a dominant orbital moment have so far remained unexplored, yet the opportunity now exists within the rare-earth nitride (REN) series, where orbital-dominant magnetism is possible due to strong spin-orbit coupling of the 4f electrons. Forming a series of mostly intrinsic ferromagnetic semiconductors, 13-19 the RENs are already integrated within spintronic devices, 20,21 and thus provide a novel system for studying competing interactions. The rare-earth elements, comprising the series across which the 4f shell is filled, have been of interest for nearly a century. They are most commonly found in the trivalent state in a wide range of compounds, including the RENs. The 4f shell, with l = 3, comprises seven distinct orbital states, −3 m l 3, and with the spin degeneracy a total of 14 single-electron states. Gd 3+ has a half filled shell, for which Hund's rules state that the seven electrons fill all of the orbital states with spin-up electrons; L = 0 and S = J = 7/2. It thus has a purely spin moment of 7 µ B . The indirect exchange interaction aligns the spins below a Curie temperature of about 50 K, rising to 70 K under heavy donor doping, 22 but the spherical symmetry of...