We present the studies of electrical transport and magnetic interactions in Zn1−xMnxGeAs2 crystals with low Mn content 0≤x≤0.042. We show that the ionic-acceptor defects are mainly responsible for the strong p-type conductivity of our samples. We found that the negative magnetoresistance with maximum values of about −50% is related to the weak localization phenomena. The magnetic properties of Zn1−xMnxGeAs2 samples show that the random Mn-distribution in the cation sites of the host lattice occurs only for the sample with the lowest Mn-content, x = 0.003. The samples with higher Mn-content show a high level of magnetic frustration. Nonzero Curie-Weiss temperature observed in all our samples indicates that weak ferromagnetic (for x = 0.003) or antiferromagnetic (for x>0.005) interactions with the Curie-Weiss temperature, |Θ|<3 K, are present in this system. The Ruderman-Kittel-Kasuya-Yosida model, used to estimate the Mn-hole exchange integral Jpd for the diluted Zn0.997Mn0.003GeAs2 sample, makes possible to estimate the value of Jpd=(0.75 ± 0.09) eV.

We present the studies of Sn1−xCrxTe semimagnetic semiconductors with chemical composition x ranging from 0.004 to 0.012. The structural characterization indicates that even at low average Cr-content x ≤ 0.012, the aggregation into micrometer size clusters appears in our samples. The magnetic properties are aected by the presence of clusters. In all our samples we observe the transition into the ordered state at temperatures between 130 and 140 K. The analysis of both static and dynamic magnetic susceptibility data indicates that the spin-glass-like state is observed in our samples. The addition of Cr to the alloy seems to shift the spin-glass-like transition from 130 K for x = 0.004 to 140 K for x = 0.012.

Magnetotransport properties of spin-glass-like Ge 1-x-y Sn x Mn y Te mixed crystals with chemical composition changing in the range of 0.083 ≤ x ≤ 0.142 and 0.012 ≤ y ≤ 0.119 are presented. The observed negative magnetoresistance we attribute to two mechanisms i.e. weak localization occurring at low fields and spin disorder scattering giving contribution mainly at higher magnetic fields. A pronounced hysteretic anomalous Hall effect (AHE) was observed. The estimated AHE coefficient shows a small temperature dependence and is dependent on Mn-content, with changes in the range of 10 −7 < R S < 10 −6 m 3 /C. The scaling law analysis has proven that the AHE in this system is due to the extrinsic mechanisms, mainly due to the skew scattering accompanied with the side jump processes.

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&lt;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&lt;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&lt;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 studies of structural, magnetic, and electrical properties of Zn1-x Mn x SnSb2+MnSb nanocomposite ferromagnetic semiconductors with the average Mn-content, [Formula: see text], changing from 0.027 up to 0.138. The magnetic force microscope imaging done at room temperature shows the presence of a strong signal coming from MnSb clusters. Magnetic properties show the paramagnet-ferromagnet transition with the Curie temperature, T C, equal to about 522 K and the cluster-glass behavior with the transition temperature, T CG, equal to about 465 K, both related to MnSb clusters. The magnetotransport studies show that all investigated samples are p-type semiconductors with high hole concentration, p, changing from 10(21) to 10(22) cm(-3). A large increase in the resistivity as a function of the magnetic field is observed at T < 10 K and small magnetic fields, [Formula: see text] mT, for all the studied samples with a maximum amplitude of the magnetoresistance about 460% at T  =  1.4 K. The large increase in the resistivity is most probably caused by the appearance of the superconducting state in the samples at T < 4.3 K.