Magnetic and transport properties of Ge(1-x-y)Mn(x)Eu(y)Te crystals with chemical compositions 0.041 < x < 0.092 and 0.010 < y < 0.043 are studied. Ferromagnetic order is observed at 150 < T < 160 K. Aggregation of magnetic ions into clusters is foun
d to be the source of almost constant, composition independent Curie temperatures in our samples. Magnetotransport studies show the presence of both negative (at T < 25 K) and linear positive (for 25<T <200 K) magnetoresistance effects (with amplitudes not exceeding 2%) in the studied alloy. Negative magnetoresistance detected at T < 25 K is found to be due to a tunneling of spin-polarized electrons between ferromagnetic clusters. A linear positive magnetoresistance is identified to be geometrical effect related with the presence of ferromagnetic clusters inside semiconductor matrix. The product of the polarization constant and the inter-grain exchange constant, J_P, varies between about 0.13 meV and 0.99 meV. Strong anomalous Hall effect (AHE) is observed for T < T_C with coefficients R_S independent of temperature. The scaling analysis of the AHE leads to a conclusion that this effect is due to a skew scattering mechanism.
We present the studies of electrical transport and magnetic interactions in Zn_{1-x}Mn_{x}GeAs_{2} crystals with low Mn content 0 leq x leq 0.043. We show that the ionic-acceptor defects are mainly responsible for the strong p-type conductivity of ou
r samples. We found that the negative magnetoresistance (MR) 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 |{Theta}|<3 K are present in this system. The RKKY model, used to estimate the Mn-hole exchange integral Jpd for the diluted Zn/0.997/Mn/0.003/GeAs/2/ sample, makes possible to estimate the value of Jpd =(0.75+/-0.09) eV.
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 10E-7 < R_S < 10E-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 2 MeV 4He+-irradiated GaN grown by metal-organic chemical-vapor deposition. Particle irradiation allowed controllable introduction of Ga-vacancy in the samples. The magnetic moments with concentrations
changing between 4.3...8.3x10^17 cm^-3 showing superparamagnetic blocking at room temperature are observed. The appearance of clear hysteresis curve at T = 5 K with coercive field of about H_C = 270 Oe suggests that the formation of more complex Ga vacancy related defects is promoted with increasing Ga vacancy content. The small concentration of the observed magnetically-active defects with respect to the total Ga- vacancy concentration suggests that the presence of the oxygen/hydrogen-related vacancy complexes is the source of the observed magnetic moments.
