S. Mazur

Correlation between the negative magnetoresistance effect and magnon excitations in single-crystalline CuCr1.6V0.4Se4

Structural, electrical and magnetic measurements, as well as electron spin resonance (ESR) spectra, were used to characterise the single-crystalline CuCr1.6V0.4Se4 spinel and study the correlation between the negative magnetoresistance effect and magnon excitations. We established the ferromagnetic order below the Curie temperature T C ≈ 193 K, a p-type semiconducting behaviour, the ESR change from paramagnetic to ferromagnetic resonance at T C, a large ESR linewidth value and its temperature dependence in the paramagnetic region. Electrical studies revealed negative magnetoresistance, which can be enhanced with increasing magnetic field and decreasing temperature, while a detailed thermopower analysis showed magnon excitations at low temperatures. Spin–phonon coupling is explained within the framework of a complex model of paramagnetic relaxation processes as a several-stage relaxation process in which the V3+ ions, the exchange subsystem and conduction electron subsystem act as the intermediate reservoirs.

Electrical resistivity dip in Sb x V y Mo z O t phases

Electrical resistivity dips have been discovered in the temperature range 100–500 K both in the SbVO4.96 matrix and the Sb x V y Mo z O t phases for 10 mol% solubility of MoO3 in SbVO5. As the Sb content increases and simultaneously the V content decreases, the value of the resistivity at the dip, ρ d, decreases and shifts the dip to higher temperatures. The magnetic measurements showed a spontaneous magnetization and parasitic magnetism of the solid solutions under study. Characteristic for parasitic magnetism is a small value of the magnetic moment, here 0.014 μ B/f.u. at 4.2 K and at a magnetic field of 14 T as well as a small value of the mass susceptibility, here 10−5 cm3/g. The value of the Néel temperature, T N ≤ 8 K, and the Curie–Weiss temperature, θ CW ≤ −208 K, indicate a collinear antiferromagnetic (AFM) order. We suggest that neither the magnetism nor the Mo-content can be correlated with the resistivity anomalies. Therefore, these effects may rather be interpreted in terms of a small-polaron gas in the resistivity dip area. Alternatively, they could mark a lattice/electronic entropy-driven incomplete metal–insulator transition.