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We report on magnetic properties and X-band electron spin resonance (ESR) study (80-430 K) of diluted magnetic semiconductors Ge1-xMnxTe (x=0.07-0.44) revealing ferromagnetism with the Curie temperature achieving 90 K. Effective magnetic moment peff per Mn2+ ion estimated from the Curie constant in the range 0.15≤x≤0.26 increases from 2.27 to 2.95 μB. The temperature evolution of ESR spectra was found to have a complicated character. We observed the presence of two distinct absorption lines of Dysonian type, associated with two resonance centers in these diluted magnetic semiconductors. Possible origin of these two lines has been analyzed and clustering effect was proposed to be most likely responsible for anomalous behavior. Anomalies in temperature dependencies of the linewidths and g-factors were observed at temperatures lower than 160 K. We connect these anomalies with magnetic fluctuations in the vicinity of transition to ferromagnetic phases. The anomalous broadening of the linewidth in paramagnetic region occurs with decreasing of the temperature similarly to ESR behavior of related A 2MnB6 diluted magnetic semiconductors. This broadening is satisfactorily described in the framework of modified Huber's theory. At the same time, the g-factor is essentially independent on both temperature and alloy composition. Average values of effective g-factor for two resolved spectral components at room temperature were found to be g1=2.02-2.07 and g2≈1.99. [ABSTRACT FROM AUTHOR]

The temperature dependences of the Hall coefficient (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) in PbGeCrTe alloys ( x = 0.03-0.08, y ≤ 0.01) are studied. An increase in the absolute value of the Hall coefficient with an increase in temperature is found. This fact is indicative of a decrease in the concentration of free electrons as a result of the motion of the resonant level of chromium stabilizing the Fermi level relative to the conduction-band bottom. The temperature dependences of the Hall coefficient, in satisfactory agreement with the experimental ones, are calculated in the context of the two-band Kane dispersion law allowing for the structural phase transition upon increasing temperature. The energy position and temperature coefficients of the motion of the resonant level of chromium relative to the middle of the band gap in the rhombohedral and cubic phases are determined. [ABSTRACT FROM AUTHOR]

Magnetic properties of Pb1 − x − yGe xCr y Te alloys ( x = 0.02–0.20, y = 0.01–0.08) were studied. It was detected that the magnetic susceptibility of alloys consists of two contributions: the paramagnetic Curie-Weiss part (the temperature region is T < 50 K) caused, probably, by the Cr3+ ion paramagnetism, and the high-temperature ferromagnetic part ( T < 300 K). The dependences of the concentration of magnetic centers on the composition of the matrix were obtained from the paramagnetic and ferromagnetic contributions. It was shown that a decrease in the concentration of paramagnetic centers can be, at least qualitatively, explained by the transformation of the electronic structure as the germanium concentration increases. A phenomenological model was suggested, which explains the behavior of magnetic properties as the chromium content increases, and possible mechanisms of ferromagnetic ordering in studied alloys are discussed. [ABSTRACT FROM AUTHOR]

A study is reported of the nuclear magnetic resonance spectra of [sup 119]Sn and [sup 125]Te in SnTe with hole concentrations p[sub 77] = 1.42 × 10[sup 20] - 2.3 × 10[sup 21] cm[sup -3] and in SnTe:Mn (N[sub Mn] = 0.5 and 5 at. %, p[sub 77] = 8 × 10[sup 20] cm[sup -3]) at T = 4.2-300 K. Considerable broadening of NMR lines due to hyperfine magnetic interactions between nuclear and electron spins was observed in SnTe with p[sub 77] > 2×[sup 20] cm[sup -3]. Asymmetric broadening of the resonance lines was observed in the rhombohedral phase of SnTe and SnTe:Mn. The temperature dependence of the NMR line width of [sup 125]Te in SnTe:Mn is in agreement with the magnetic phase diagram for N[sub Mn] = 5 at. %. The superparamagnetic phase of SnTe:Mn is formed at T = 20 ± 2 K and the ferromagnetic phase is formed at T = 4.2 K. [ABSTRACT FROM AUTHOR]