A. Avdonin

Homogeneous limit of Cd1−xMnxGeAs2 alloy: Electrical and magnetic properties

We present the studies of structural, electrical, and magnetic properties of bulk Cd1−xMnxGeAs2 crystals with low Mn content, x, varying from 0 to 0.037. The studied samples have excellent crystallographic quality indicated by the presence of diffraction patterns never before observed experimentally for this compound. The electrical transport in our samples is dominated by thermal activation of conducting holes from the impurity states to the valence band with activation energy of about 200 meV. The defect states acting as ionic scattering centers with concentration in the range from 6 to 15 × 1017 cm−3 are observed. The effective Mn content in our samples, x¯θ, determined from fit of the susceptibility data to the Curie-Weiss law, is very close to the average chemical content, x. It indicates that the Mn ions are distributed randomly, substituting the Cd sites in the host CdGeAs2 lattice. We observe a negative Curie-Weiss temperature, |θ|≤3.1 K, increasing as a function of x. This indicates the significa...

Low-dilution limit of Zn1−xMnxGeAs2: Electrical and magnetic properties

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 ...

Negative magnetoresistance and anomalous Hall effect in GeMnTe-SnMnTe spin-glass-like system

Magnetotransport properties of spin-glass-like Ge1−x−ySnxMnyTe 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<RS<10−6m3/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.

Cluster altered magnetic and transport properties in Ge1−x−yMnxEuyTe

Magnetic and transport properties of Ge{sub 1−x−y}Mn{sub x}Eu{sub 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 found to be the source of almost constant, composition independent Curie temperatures in our samples. Magnetotransport studies show that below 25 K there is a negative magnetoresistance, which is not linear and has a minimum and above 60 K the magnetoresistance is positive and linear. 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 a geometrical effect related to the presence of ferromagnetic clusters inside the semiconductor matrix. The product of the polarization constant (P) and the inter-grain exchange constant (J), JP, varies between about 0.13 meV and 0.99 meV. A strong anomalous Hall effect is observed for T ≤ T{sub C}, where T{sub C} is the Curie temperature, with coefficients R{sub S} independent of temperature. The scaling analysis of the AHE leads to a conclusion that this effect is due to a skew scattering mechanism.

Magnetoresistance control in granular Zn1-x-y CdxMnyGeAs2 nanocomposite ferromagnetic semiconductors

We present studies of structural, magnetic, and electrical properties of Zn1-x-y CdxMnyGeAs2 nanocomposite ferromagnetic semiconductor samples with changeable chemical composition. The presence of MnAs clusters induces the studied alloy room temperature ferromagnetism with the Curie temperature, TC, around 305 K. The chemical composition of the chalcopyrite matrix controls the geometrical parameters of the clusters, inducing different magnetoresistance effects in the crystals. The presence of ferromagnetic clusters in the alloy induces either negative or positive magnetoresistance with different values. The Cd-content allows a change of magnetoresistance sign in our samples from negative (for x≈0.85) to positive (for x≈0.12). The negative magnetoresistance present in the samples with x≈0.85 is observed at temperatures T<25 K with maximum values of about −32% at T=1.4 K and B=13 T, strongly depending on the Mn content, y. The positive magnetoresistance present in the samples with x≈0.12 is observed with ma...

Electroluminescence and positive magnetoresistance near the Curie–Weiss temperature in the Zn1−xMnxTe light emitting devices

The light emitting devices (LEDs) based on the p-Zn1−xMnxTe bicrystals have been fabricated. The Zn1−xMnxTe LEDs produce red and green emission originated from the internal d-shell transitions of the Mn2+ ions and the donor-acceptor-pairs recombination, respectively. The presence of the acceptor bound magnetic polarons and their clusters in the Zn1−xMnxTe crystals near the Curie–Weiss temperature was observed. It induces a critical behavior of the magnetic field dependence of the green emission intensity and a positive magnetoresistance in the Zn1−xMnxTe LEDs.

Cluster altered magnetic and transport properties in Ge{sub 1−x−y}Mn{sub x}Eu{sub y}Te

Magnetic and transport properties of Ge{sub 1−x−y}Mn{sub x}Eu{sub 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 found to be the source of almost constant, composition independent Curie temperatures in our samples. Magnetotransport studies show that below 25 K there is a negative magnetoresistance, which is not linear and has a minimum and above 60 K the magnetoresistance is positive and linear. 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 a geometrical effect related to the presence of ferromagnetic clusters inside the semiconductor matrix. The product of the polarization constant (P) and the inter-grain exchange constant (J), JP, varies between about 0.13 meV and 0.99 meV. A strong anomalous Hall effect is observed for T ≤ T{sub C}, where T{sub C} is the Curie temperature, with coefficients R{sub S} independent of temperature. The scaling analysis of the AHE leads to a conclusion that this effect is due to a skew scattering mechanism.