Single crystals of SrFe2As2 grown using a self-flux solution method were characterized via x-ray, transport, and magnetization studies, revealing a superconducting phase below Tc=21 K characterized by a full electrical resistivity transition and partial diamagnetic screening. The reversible destruction and reinstatement of this phase by heat treatment and mechanical deformation studies, along with single-crystal x-ray diffraction measurements, indicate that internal crystallographic strain originating from c-axis-oriented planar defects plays a central role in promoting the appearance of superconductivity under ambient-pressure conditions in approximately 90% of as-grown crystals. The appearance of a ferromagnetic moment with magnitude proportional to the tunable superconducting volume fraction suggests that these phenomena are both stabilized by lattice distortion.

No abstract

No abstract

The question of structural disorder and its effects on magnetism is relevant to a number of spin liquid candidate materials. Although commonly thought of as a route to spin glass behaviour, here we describe a system in which the structural disorder results in long-range antiferromagnetic order due to local symmetry breaking. Nd2ScNbO7 is shown to have a dispersionless gapped excitation observed in other neodymium pyrochlores below T N = 0.37 K through polarized and inelastic neutron scattering. However the dispersing spin waves are not observed. This excited mode is shown to occur in only 14(2)% of the neodymium ions through spectroscopy and is consistent with total scattering measurements as well as the magnitude of the dynamic moment 0.26(2) μ B . The remaining magnetic species order completely into the all-in all-out Ising antiferromagnetic structure. This can be seen as a result of local symmetry breaking due disordered Sc+3 and Nb+5 ions about the A-site. From this work, it has been established that B-site disorder restores the dipole-like behaviour of the Nd+3 ions compared to the Nd2B2O7 parent series.

No abstract

No abstract

We present the studies of magnetic properties of Ge1-xCrxTe diluted magnetic semiconductor with changeable chemical composition 0.016≤x≤0.061. A spin-glass state (at T≤35 K) for x = 0.016 and 0.025 and a ferromagnetic phase (at T<60 K) for x≥0.030 are observed. The long range carrier-mediated magnetic interactions are found to be responsible for the observed magnetic ordering for x<0.045, while for x≥0.045 the spinodal decomposition of Cr ions leads to a maximum and decrease of the Curie temperature, TC, with increasing x. The calculations based on spin waves model are able to reproduce the observed magnetic properties at a homogeneous limit of Cr alloying, e.g., x<0.04, and prove that carrier mediated Ruderman-Kittel-Kasuya-Yosida interaction is responsible for the observed magnetic states. The value of the Cr-hole exchange integral, Jpd, estimated via fitting of the experimental results with the theoretical model, is in the limits 0.77…0.88 eV.

We present the experimental evidence for the presence of spinodal decomposition of the magnetic ions