FeGa 3 is an unusual intermetallic semiconductor that presents intriguing magnetic responses to the tuning of its electronic properties. When doped with Ge, the system evolves from diamagnetic to paramagnetic to ferromagnetic ground states that are not well understood. In this work, we have performed a joint theoretical and experimental study of FeGa 3−x Ge x using Density Functional Theory and magnetic susceptibility measurements. For low Ge concentrations we observe the formation of localized moments on some Fe atoms and, as the dopant concentration increases, a more delocalized magnetic behavior emerges. The magnetic configuration strongly depends on the dopant distribution, leading even to the appearance of antiferromagnetic interactions in certain configurations.

The structural properties of insulating α-NaYF 4 (cubic) nanoparticles with size ranging within 4 -25 nm were investigated by high-resolution 23 Na and 19 F solid-state Nuclear Magnetic Resonance (NMR) spectroscopy under magic angle spinning (MAS) with single pulse (SP-MAS), spin-echo (SE-MAS), inversion recovery, and 3Q-MAS

A detailed microscopic and quantitative description of the electronic and magnetic properties of Gd 3+ -doped YCo2Zn20 single crystals (Y1−xGdxCo2Zn20: (0.002 x ≤ 1.00) is reported through a combination of temperature-dependent electron spin resonance (ESR), heat capacity and dc magnetic susceptibility experiments, plus first-principles density functional theory (DFT) calculations. The ESR results indicate that this system features an exchange bottleneck scenario wherein various channels for the spin-lattice relaxation mechanism of the Gd 3+ ions can be identified via exchange interactions with different types of conduction electrons at the Fermi level. Quantitative support from the other techniques allow to extract the exchange interaction parameters between the localized magnetic moments of the Gd 3+ ions and the different types of conduction electrons present at the Fermi level (J f s , J f p and J f d ). Despite the complexity of the crystal structure, our combination of experimental and electronic structure data establish GdCo2Zn20 as a model RKKY system by predicting a Curie-Weiss temperature θC = −1.2(2) K directly from microscopic parameters, in very good agreement with the bulk value from magnetization data. The successful microscopic understanding of the electronic structure and behavior for the two end compounds YCo2Zn20 and GdCo2Zn20 means they can be used as references to help describe the more complex electronic properties of related materials.

Temperature dependent magnetization, muon spin rotation and 57 Fe Mössbauer spectroscopy experiments performed on crystals of intermetallic 0.14, 0.17, 0.22, 0.27, 0.29, 0.32) are reported. Whereas at y = 0.11 even a sensitive magnetic microprobe such as µSR does not detect magnetism, all other samples display weak ferromagnetism with a magnetic moment of up to 0.22 µB per Fe atom. As a function of doping and of temperature a crossover from short range to long range magnetic order is observed, characterized by a broadly distributed spontaneous internal field. However, the y = 0.14 and y = 0.17 remain in the short range ordered state down to the lowest investigated temperature. The transition from short range to long range order appears to be accompanied by a change of the character of the spin fluctuations, which exhibit spin wave excitations signature in the LRO part of the phase diagram. Mössbauer spectroscopy for y = 0.27 and 0.32 indicates that the internal field lies in the plane perpendicular to the crystallographic c axis. The field distribution and its evolution with doping suggest that the details of the Fe magnetic moment formation and the consequent magnetic state are determined not only by the dopant concentration but also by the way the replacement of the Ga atoms surrounding the Fe is accomplished.

No abstract