We report 51 V zero-field NMR of the manganese vanadate spinel compound, MnV 2 O 4 , together with both ac and dc magnetization measurements. The field and temperature dependences of ac susceptibilities show a re-entrant-spin-glass-like behavior below the ferrimagnetic (FEM) ordering temperature. The zero-field NMR spectrum consists of multiple lines ranging from 240 to 320 MHz. Its temperature and field dependences are discussed in terms of the persistence of a small fraction of the cubic phase within the FEM ordered ground state. Due to strong spin-orbit couplings the disordered phase induces an anomalous structural and electronic state in an external field. This suggests a close correlation between magnetism and structure.

The transition metal (TM) chalcogenides of the form TMX(2) (X = S or Se) have been studied for decades due to their interesting electronic and magnetic properties such as metamagnetism and metal-insulator transitions. In particular, the Co(1-x)Fe(x)S(2) alloys were the subject of investigation in the 1970s due to general interest in itinerant ferromagnetism. In recent years (2000-present) it has been shown, both by electronic structure calculations and detailed experimental investigations, that Co(1-x)Fe(x)S(2) is a model system for the investigation of highly spin polarized ferromagnetism. The radically different electronic properties of the two endpoint compounds (CoS(2) is a narrow bandwidth ferromagnetic metal, while FeS(2) is a diamagnetic semiconductor), in a system forming a substitutional solid solution allows for composition control of the Fermi level relative to the spin split bands, and therefore composition-controlled conduction electron spin polarization. In essence, the recent work has shown that the concept of 'band engineering' can be applied to half-metallic ferromagnets and that high spin polarization can be deliberately engineered. Experiments reveal tunability in both sign and magnitude of the spin polarization at the Fermi level, with maximum values obtained to date of 85% at low temperatures. In this paper we review the properties of Co(1-x)Fe(x)S(2) alloys, with an emphasis on properties of relevance to half-metallicity. Crystal structure, electronic structure, synthesis, magnetic properties, transport properties, direct probes of the spin polarization, and measurements of the total density of states at the Fermi level are all discussed. We conclude with a discussion of the factors that influence, or even limit, the spin polarization, along with a discussion of opportunities and problems for future investigation, particularly with regard to fundamental studies of spintronic devices.

Inhomogeneous electronic states resulting from entangled spin, charge, and lattice degrees of freedom are hallmarks of strongly correlated electron materials; such behavior has been observed in many classes of d-electron materials, including the high-T c copperoxide superconductors, manganites, and most recently the ironpnictide superconductors. The complexity generated by competing phases in these materials constitutes a considerable theoretical challenge-one that still defies a complete description. Here, we report a manifestation of electronic inhomogeneity in a strongly correlated f-electron system, using CeCoIn 5 as an example. A thermodynamic analysis of its superconductivity, combined with nuclear quadrupole resonance measurements, shows that nonmagnetic impurities (Y, La, Yb, Th, Hg, and Sn) locally suppress unconventional superconductivity, generating an inhomogeneous electronic "Swiss cheese" due to disrupted periodicity of the Kondo lattice. Our analysis may be generalized to include related systems, suggesting that electronic inhomogeneity should be considered broadly in Kondo lattice materials.Kondo effect | heavy fermion E lectronic inhomogeneity is commonplace in materials in which strong correlations among electrons produce electronic states that compete with one another on multiple length scales (1). One early indication of such heterogeneity came from studies of the high-T c cuprate superconductors in which nonmagnetic Zn impurities were introduced into the CuO 2 planes of YBa 2 Cu 3 O 6þx (YBCO) and La 2-x Sr x CuO 4 ðLSCOÞ 2 ; the anomalous suppression of the superfluid density of the superconducting condensate was explained within a Swiss cheese model comprised of normal regions around the impurity that healed over a (short) coherence length of order 20 Å within a superconducting matrix (2), later verified by scanning tunneling spectroscopy (3). Not only is superconductivity locally suppressed in the Swiss cheese regions, but new electronic states emerge, such as impurity resonances and other exotic forms of electronic inhomogeneity (e.g., "stripe" and "checkerboard" phases) observed in cuprates and also in other d-electron materials (e.g., manganites) (1, 4). In contrast, electronic inhomogeneity has rarely been considered in the prototypical correlated system: f -electron materials (5) in which itinerant heavy quasiparticles emerge at low temperature due to a periodic lattice of Kondo ions. In this work, we investigate the underlying electronic structure of the Kondo lattice compound CeCoIn 5 whose heavy quasiparticles pair to create a d-wave superconducting state below 2.3 K (6). As will be discussed, the superconductivity itself serves as a mirror that reflects the presence of electronic inhomogeneity. A thermodynamic analysis of high-purity single crystals of CeCoIn 5 , doped with different impurities (Y 3þ , La 3þ , Yb 2þ , Th 4þ , Hg, and Sn), reveals that lattice sites filled by these impurities create "Kondo holes" (7, 8) that produce a nonsuperconducting component within the superc...

This work presents 75 As NMR spin-echo decay rate (1/T 2 ) measurements in Ba(Fe 1−x Rh x ) 2 As 2 superconductors, for 0.041 x 0.094. It is shown that 1/T 2 increases upon cooling, in the normal phase, suggesting the onset of an unconventional very low-frequency activated dynamic. The correlation times of the fluctuations and their energy barriers are derived. The motion is favored at large Rh content, while it is hindered by the application of a magnetic field perpendicular to the FeAs layers. The same dynamic is observed in the spin-lattice relaxation rate, in a quantitatively consistent manner. These results are discussed in the light of nematic fluctuations involving domain wall motion. The analogies with the behavior observed in the cuprates are also outlined.