Investigation of electrical and magnetic properties of triangular antiferromagnets.

We have synthesized magnetic Fe-doped NiGa2S4 and investigated its electrical and magnetic properties with a superconducting quantum-interference device magnetometer, Mössbauer spectroscopy, and a physical property measurement system. X-ray diffraction analysis at room temperature shows that the prepared samples are single phase with trigonal structure (P-3m1). From zero-field-cooled (ZFC) and field-cooled magnetization curves under 100 Oe between 4.2 and 200 K, we have measured the temperature-dependent susceptibility χ of Ni1-xFexGa2S4. A cusp is observed in the ZFC measurement for the samples with x ≥ 0.1, which is due to the spin-freezing effect in the spin-glass system. Moreover, with increasing Fe concentration, the sample shows the antiferromagnetic behavior and the increase in freezing temperature Tf. This, in turn, suggests that the spin-averaged value of the sample increases and antiferromagnetic spin-spin interaction becomes stronger with Fe concentration. The temperature-dependent resistance of semiconducting Ni1-xFexGa2S4 (x = 0.3, 0.5, 0.7, 0.9) follows Arrhenius law R = R0exp(E0/kBT) for the semiconducting temperature, with the gap energies E0 of 210.6, 192.0, 135.6, and 126.4 meV, respectively. This increase in gap energy comes from the distortion of octahedral structure in the a-b plane direction. [ABSTRACT FROM AUTHOR]