Surface magnetism of Gd(0001) films: Evidence for an unexpected phase transition

The Effects of Substrate Temperature on the Growth, Microstructural and Magnetic Properties of Gadolinium-Containing Films on Aluminum Nitride

To facilitate future novel devices incorporating rare earth metal films and III-V semiconductors on Si substrates, this study investigates the mechanisms of growth via molecular beam epitaxy of gadolinium (Gd) on aluminum nitride (AlN) by determining the impact of substrate temperature on microstructure. The Gd films underwent extensive surface analysis via in situ reflective high energy electron diffraction (RHEED) and ex-situ SEM and AFM. Characterization of the surface features of rare earth metal films is important, as surface geometry has been shown to strongly impact magnetic properties. SEM and AFM imaging determined that Gd films grown on AlN (0001) from 80 °C to 400 °C transition from wetting, nodular films to island–trench growth mode to reduce in-plane lattice strain. XRD and Raman spectroscopy of the films revealed that they were primarily comprised of GdN, Gd and Gd2O3. The samples were also analyzed by a vibrating sample magnetometer (VSM) at room temperature. From the room temperature magnetic studies, the thick films showed superparamagnetic behavior, with samples grown between 240 °C and 270 °C showing high magnetic susceptibility. Increasing GdN (111) 2θ peak position and single-crystal growth modes correlated with increasing peak magnetization of the thin films, suggesting that lattice strain in single-crystal films was the primary driver of enhanced magnetic susceptibility.

Pulsed laser assisted synthesis of gadolinium carbide/carbon shell dots with enhanced magnetic resonance properties

There is now the opportunity for nanomaterials to be utilized in bioapplications with low toxicity, good stability and fine dissolvability. Herein, we present a pulsed laser assisted carbon coating method for nanocrystals, and gadolinium carbide/carbon shell (GC/CS) dots with a face-centered cubic structured gadolinium carbide core that have been synthesized in toluene. Good stability of the GC/CS dots was observed, not only in ethanol but also in the immunoconjugates. The MTT assay revealed immunoconjugates with non/low cytotoxicities. As a type of paramagnetic species, the GC/CS dots revealed excellent enhancement in magnetic resonance imaging at a high magnetic field of 14.1 T at ultra-low concentrations. In terms of the relaxivity values of the 1-3 nm GC/CS sample, both [Formula: see text] and [Formula: see text] have been dramatically increased to 86.5 mM^-1 s^-1 and 107.3 mM^-1 s^-1, respectively, thereby demonstrating the great potential for GC/CS dots to be utilized as advanced magnetic resonance agents for the diagnosis of cancers.

Strain-induced effects in the electronic and spin properties of a monolayer of ferromagnetic GdAg2

We report on the structural, electronic and magnetic properties of a monolayer of GdAg₂, forming a moiré pattern on Ag(111). Combining scanning tunneling microscopy and ab initio spin-polarized calculations, we show that the electronic band structure can be shifted linearly via thermal controlled strain of the intra-layer atomic distance in the range of 1-7%, leading to lateral hetero-structuring. Furthermore, the coupling of the incommensurable GdAg₂ alloy layer to the Ag(111) substrate leads to spatially varying atomic relaxation causing subsurface layer buckling, texturing of the electronic and spin properties, and inhomogeneity of the magnetic anisotropy energy across the layer. These results provide perspectives for control of electronic properties and magnetic ordering in atomically-thin layers.

Magnetism and exchange interaction of small rare-earth clusters; Tb as a representative

Here we follow, both experimentally and theoretically, the development of magnetism in Tb clusters from the atomic limit, adding one atom at a time. The exchange interaction is, surprisingly, observed to drastically increase compared to that of bulk, and to exhibit irregular oscillations as a function of the interatomic distance. From electronic structure theory we find that the theoretical magnetic moments oscillate with cluster size in exact agreement with experimental data. Unlike the bulk, the oscillation is not caused by the RKKY mechanism. Instead, the inter-atomic exchange is shown to be driven by a competition between wave-function overlap of the 5d shell and the on-site exchange interaction, which leads to a competition between ferromagnetic double-exchange and antiferromagnetic super-exchange. This understanding opens up new ways to tune the magnetic properties of rare-earth based magnets with nano-sized building blocks.

Strong ferromagnetism at the surface of an antiferromagnet caused by buried magnetic moments

Carrying a large, pure spin magnetic moment of 7 μB per atom in the half-filled 4f shell, divalent europium is an outstanding element for assembling novel magnetic devices in which a two-dimensional electron gas may be polarized due to exchange interaction with an underlying magnetically-active Eu layer. Here we show that the Si-Rh-Si surface trilayer of the antiferromagnet EuRh2Si2 bears a surface state, which exhibits an unexpected and large spin splitting controllable by temperature. The splitting sets in below ~32.5 K, well above the ordering temperature of the Eu 4f moments (~24.5 K) in the bulk, indicating a larger ordering temperature in the topmost Eu layers. The driving force for the itinerant ferromagnetism at the surface is the aforementioned exchange interaction. Such a splitting may also be induced into states of functional surface layers deposited onto the surface of EuRh2Si2 or similarly ordered magnetic materials with metallic or semiconducting properties.

Gd(0001): A semi-infinite three-dimensional heisenberg ferromagnet with ordinary surface transition

By comparing the surface and bulk magnetization of smooth, well-ordered Gd samples, we show that the surface has an ordinary transition, i.e., a common Curie temperature for surface and bulk. A quantitative statistical analysis of the temperature dependent magnetization is presented. Critical exponents for both surface, beta(S) = 0.83+/-0.04, and bulk, beta(B) = 0.376+/-0.015, are consistent with the semi-infinite three-dimensional Heisenberg model with homogeneous exchange.