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Magnetic nanocomposites based on MnAs clusters embedded in a chalcopyrite host usually do not exhibit large magnetoresistance (MR) at room temperature, while pronounced effects are localized at very low temperatures. In the present work, we observed an appearance of large pressure-induced negative and positive MR at room temperature in the Zn0.1Cd0.9GeAs2 hybrid system containing 10% MnAs inclusions. With the applied pressure, a substantial modification of the electron transport from semimetallic to semiconducting type occurs, followed by a subsequent structural transition at P ≈ 3.5 GPa into almost metallic high-pressure phase. This picture is simultaneously supported by temperature-dependent and room temperature high-pressure transport measurements. Using a semiempirical expression, taking into account a spin-dependent scattering of charge carriers due to MnAs nanoclusters, as well as a two-band conductivity model, we have been able to partially describe the observed MR effects. The predominantly weak positive contribution at P = 1 GPa, which is well described in the framework of the proposed approach indicates the presence of spin-polarized charge carriers. Based on the two-band model calculations, a negative spin polarization was found at P ≥ 3 GPa that ascribed to a structural change of the matrix. As our results indicate, an emerging MR in the structural transition region is characterized by a complex behavior. In particular, the negative part of MR demonstrates a magnetic field dependence different than Δρ/ρ0 ∼ H2, suggesting the presence of unusual scattering mechanisms in magnetotransport. I. INTRODUCTION

We present studies of the influence of the chemical composition changes on the type of magnetic order present in bulk nanocomposite Ge 1− x−y Pb x Cr y Te crystals with the average Pb-content close to x ≈ 0.20 and Cr-content, y , varying from y = 0.017 up to 0.043. Detailed magnetometric studies revealed the existence of two ordered magnetic states present in all our samples. All our crystals show a paramagnet to spin-glass-like state transition at temperatures from 135 K to 145 K, related to the presence of Cr 5 Te 8 clusters in the host lattice. The second transition type depends on the Cr-content, y . In the case of samples with y equal to 0.038 and 0.043 the ferromagnetic phase is observed with T C slightly below 70 K, while in samples with lower chromium concentration the presence of spin-glass-like state slightly below 50 K is observed. The presence of clusters in our samples has significant impact on the carrier transport and magnetotransport in our samples. The presence of critical scattering on the magnetic impurities is observed in resistivity and magnetoresistance data. Nearly-linear magnetoresistance is also observed in our samples indicating a presence of strong scattering on the grain boundaries in our samples.

We present studies of magnetotransport properties of Ge 1− x − y Pb x Mn y Te bulk crystals with chemical composition changing from 0.180 x y T SG around 90 K. The presence of strong anomalous Hall effect (AHE) with hysteresis is observed at T T SG . The data analysis allowed calculation of a correction to the Hall constant R H for T T SG and the AHE constant, R S . R S is around 10 −6 m 3 /C. R S and R H do not change strongly with temperature. The scaling law analysis has proved that the AHE in this system is due to the extrinsic mechanisms dominated by the skew scattering with relatively small contribution of the side jump process. Strong localization occurs in our system at T T SG and causes a presence of a minimum in the resistivity vs. temperature dependence. The magnetoresistance of our samples shows complex behavior at T T SG . The negative magnetoresistance is observed at T T nearly linear positive magnetoresistance is observed at temperatures from 20 K up to T ≈ T SG , where it reaches maximum. Positive linear magnetoresistance is related to the granular nature of our samples while the maximum near T SG is related to the giant spin-splitting of the valence band.

We present the studies of structural, electrical, and magnetic properties of bulk Sn 1 − x − y Cr x Eu y Te crystals with different chemical compositions varying in the range of 0.004 ≤ x ≤ 0.089 and 0.007 ≤ y ≤ 0.020. The structural characterization of our samples indicated the clustering of the Cr-ions into Cr–Te related clusters. Eu ions do not form clusters and are randomly distributed in the SnTe lattice. The magnetotransport studies show the presence of positive linear magnetoresistance with maximum amplitude of about 80% for all our samples. Positive magnetoresistance is a geometrical effect related to the presence of clusters in the SnTe lattice. The cluster-glass-like state at the temperature of about 130 K is observed for x ≤ 0.025. The cluster-glass-like state is due to the presence of Cr-rich clusters in the SnTe lattice. The ferromagnetic behavior with the Curie temperature of about 275 K is observed for the samples with x > 0.077 indicating the presence of Cr 5 Te 8 clusters in the host material. Eu ions presence in our samples shows paramagnetic behavior.

We present studies of magnetic properties of Ge 1− x − y Pb x Mn y Te bulk crystals with chemical composition varying in the range of 0.180 x y J pd , having values from 0.47 eV to 0.80 eV gives spin-glass transition temperature, T SG , values close to the experimental values for the Ge-rich phase. The magnetic order observed for the Pb-rich phase is also due to the carrier mediated magnetic interaction. The experimental transition temperatures are fitted with J pd value ranging from 0.22 eV to 0.28 eV.

Three self-assembled nanogranular composites based on MnAs ferromagnetic inclusions embedded in ZnSnAs 2 semiconductors with MnAs concentration 10, 20, 47 mol.% were synthesized. The samples were studied by X-ray, SEM, AFM, MFM and SQUID methods. It has been shown that the increasing of the MnAs concentration in composite leads to slightly increasing of the size of the magnetic inclusions. Their size depends mainly on the speed of the crystallization, but the shape of the inclusions depends on the type of the interaction between materials. The connection between equilibrium and non-equilibrium structure of the compounds has been demonstrated. Magnetic properties of the ZnSnAs 2 + MnAs samples show ferromagnetic phase transition with the Curie temperature having values from 313 K to 336 K, increasing as a function of the MnAs concentration in the nanocomposite. A small paramagnetic signal is observed at low temperatures due to individual Mn ions randomly distributed in the ZnSnAs 2 lattice. All our samples show only a narrow magnetic hysteresis loop except of the sample with 47 mol.% of MnAs, for which the coercive field increases to about 120 G. The carrier transport of the alloy shows significant influence of the MnAs clusters. All our samples have p-type conductivity with magnetotransport strongly influenced by the presence of the MnAs phase in the nanocomposite samples. The magnetoresistance (MR) of the alloy shows a complex behavior. The grain boundaries and MnAs clusters influence on the amplitude, sign, and temperature of MR.

Currently, complex ferromagnetic semiconductor systems are of significant interest due to their potential applicability in spintronics. A key feature in order to use semiconductor materials in spintronics is the presence of room temperature ferromagnetism. This feature was recently observed and is intensively studied in several Mn-alloyed II-IV-V2 group diluted magnetic semiconductor systems. The paper reviews the origin of room temperature ferromagnetism in II-IV-V2 compounds. In view of our recent reports the room temperature ferromagnetism in Mn-alloyed chalcopyrite semiconductors with more than 5 molar % of Mn is due to the presence of MnAs clusters. The solubility of magnetic impurities in bulk II-IV-V2 materials is of the order of a few percent, depending on the alloy composition. High values of the conducting hole - Mn ion exchange constant Jpd have significant value equal to 0.75 eV for Zn0.997Mn0.003GeAs2. The sample quality has significant effect on the magnetotransport of the alloy. The magnetoresistance of the alloy change main physical mechanism from spin-disorder scattering and weak localization for homogeneous samples to cluster-related geometrical effect observed for nanocomposite samples. The magnetoresistance of the II-IV-V2 alloys can be then tuned up to a few hundreds of percent via changes of the chemical composition of the alloy as well as a degree of disorder present in a material. [Projekat Ministarstva nauke Republike Srbije, br. III45003]

AIIBiνC2V semiconductors doped with Mn are perspective materials for spintronic. Structural, chemical and magnetic properties of these materials have been analyzed. The combinations of these compounds with the traditional semiconductors are perspective to create "system on chip" devices. The coexistence of ferromagnetic and paramagnetic phases was observed. The ferromagnetic phase is likely due to the presence of MnAs nanoclusters (3-5 nm). Paramagnetic properties appear due to Mn complexes (dimmer and trimmer).

The magnetic properties of a Cd1−xMnxGeAs2: MnAs hybrid micro-composite have the signature of ferromagnetic order at room temperature. Magnetotransport reveals the presence of a large linear positive magnetoresistance, with maximum values of about 550% ( B = 22 T) for x = 0.028 . This is interpreted in terms of an effective medium approximation with the value and the shape of the magnetoresistance depending on the structural and electronic properties of the semiconductor rather than on its magnetic properties. The absence of an anomalous Hall effect leads to the conclusion that ferromagnetic ordering is not the only factor necessary for the occurrence of asymmetric scattering in granular ferromagnetic materials.

The heterostructure ferromagnetic/semiconductor ZnSiAs2/Si was obtained by using the Si-ZnAs2 phase diagram. The magnetic properties of Zn1-XMnXSiAs2 bulk crystals and ferromagnetic layered heterostructures were similar. The same method was used for preparing a ferromagnetic layer ZnGeAs2 on a germanium substrate.

Based on Mn-doped chalcopyrite ZnSiAs2 the new dilute magnetic semiconductor with p-type conductivity was produced. The Curie temperature behavior of the produced semiconductor is distinctly dependent on the Mn concentration: 325 K for 1 wt.% and 337 K for 2 wt.% of Mn, consequently. Magnetization, electrical resistance, magnetic resistance and Hall effect of mentioned compositions were studied. Temperature dependence of magnetization M(T) have complicate behavior. For T  15 K the M(T) dependence is characteristic for superparamagnetic and at T > 15 K magnetization is sum of magnetizations of ensemble of superparamagnetic clusters and ferromagnetic phase contained frustration regions.

Nanocrystalline samples of ZnO doped with Fe2O3 were synthetized by wet chemical method. The series of ZnO nanosized samples in the wide range of Fe2O3 concentration (from 5 wt.% to 95 wt.%) was prepared by precipitation from nitrate solutions using ammonia. The phase composition of the samples was determined using X-ray diffraction measurements. The phases of hexagonal ZnO, and/or rhombohedric Fe2O3, and/or ZnFe2O4 were identified. The mean crystalline size of nanocrystals, determined with the use of Scherrer’s formula, varied from 8 to 52 nm. The preliminary micro-Raman spectroscopy measurements were performed. The observed features are typical of Fe doped ZnO nanoparticles. The magnetic measurements revealed the presence of different types of magnetic behavior. For samples with high Fe2O3 contents (above 70 wt.%) the ferromagnetic ordering was observed at room temperature. For samples with lower Fe2O3 contents we observed the phenomenon of superparamagnetism above the blocking temperature.

Diluted magnetic semiconductors (DMS) allows an independent control of electrical and magnetic properties by many orders of magnitude via changes in the technological parameters of the growth or post growth treatment of the compound. DMS compounds are usually developed on the basis of a III−V or II−VI semiconductor matrix into which transition metal (TM) or rare earth ions are introduced on a level of several atomic percent. IV−VI based DMS, in particular Ge1-x TM x Te alloys, possess many advantages over widely studied Ga1-x Mn x As. The carrier concentration and the amount of TM ions can be controlled independently. Moreover, the solubility of TM ions in GeTe is very high allowing growth of homogeneous Ge1-x TM x Te solid solutions over a wide range of chemical composition. Itinerant ferromagnetism can be controlled in a wide range of values reaching the Curie temperatures with a maximum of about 200 K for bulk Ge1-x Mn x Te with x = 0.5. The most important aspects of the current progress in understanding the structural, electrical, and magnetic properties of the selected representatives of Mn- and Cr-alloyed GeTe based DMS systems are reviewed. The present state of the studies of the physical mechanisms of the ferromagnetism and spin-glass-like states in Ge1-x TM x Te are described as well as the explanation of the nature of the magnetotransport effects such as negative magnetoresistance and anomalous Hall effect in Ge1-x TM x Te solid solutions.

Room-temperature ferromagnetism in Mn-doped chalcopyrites is a desire aspect when applying those materials to spin electronics. However, dominance of high Curie-temperatures due to cluster formation or inhomogeneities limited their consideration. Here we report how an external perturbation such as applied hydrostatic pressure in CdGeP₂:Mn induces a two serial magnetic transitions from ferromagnet to non-magnet state at room temperature. This effect is related to the unconventional properties of created MnP magnetic clusters within the host material. Such behavior is also discussed in connection with ab initio density functional calculations, where the structural properties of MnP indicate magnetic transitions as function of pressure as observed experimentally. Our results point out new ways to obtain controlled response of embedded magnetic clusters.

We present the experimental evidence for the presence of spinodal decomposition of the magnetic ions in the Ge/1-x-y/Cr/x/Eu/y/Te samples with chemical composition varying in the range of 0.015 < x < 0.057 and 0.003 < y < 0.042. The ferromagnetic transition at temperatures 50 < T < 57 K was observed, independent of the chemical composition. The long-range carrier mediated itinerant magnetic interactions seem to be responsible for the observed ferromagnetic order. The magnetic irreversibility with coercive field H/C/ = 5?63 mT and the saturation magnetization M/S/ 2?6 emu/g are found to strongly depend on the chemical composition of the alloy., 4 pages, 4 figures

We investigated the nature of the magnetic phase transition in ${\text{Ge}}_{1\ensuremath{-}x\ensuremath{-}y}{\text{Sn}}_{x}{\text{Mn}}_{y}\text{Te}$ mixed crystals with chemical composition changing in the range of $0.083\ensuremath{\le}x\ensuremath{\le}0.142$ and $0.012\ensuremath{\le}y\ensuremath{\le}0.119$. The dc magnetization measurements performed in magnetic fields up to 90 kOe and temperature range 2--200 K showed that the magnetic ordering at temperatures below $T=50\text{ }\text{K}$ exhibits features characteristic for both spin-glass and ferromagnetic phases. The modified Sherrington-Southern model was applied to explain the observed transition temperatures. The calculations showed that the spin-glass state is preferred in the range of the experimental carrier concentrations and Mn contents. The value of the Mn hole exchange integral was estimated to be ${J}_{pd}=0.45\ifmmode\pm\else\textpm\fi{}0.05\text{ }\text{eV}$. The experimental magnetization vs temperature curves were reproduced satisfactorily using the noninteracting spin-wave theory with the exchange constant ${J}_{pd}$ values consistent with those calculated using modified Sherrington-Southern model. The magnetization vs magnetic field curves showed nonsaturating behavior at magnetic fields $Bl90\text{ }\text{kOe}$ indicating the presence of strong magnetic frustration in the system. The experimental results were reproduced theoretically with good accuracy using the molecular-field-approximation-based model of a disordered ferromagnet with long-range Ruderman-Kittel-Kasuya-Yosida interaction.

We present studies of structural, magnetic and electrical properties of Zn/1-x-y/Cd/x/Mn/y/GeAs/2/ nanocomposite ferromagnetic semiconductor samples with changeable chemical composition. The presence of MnAs clusters induces in 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 maximum values not exceeding 50% at B =13 T and T = 4.3 K, changing with the Mn content, y., 8 pages, 7 figures

We present studies of magnetic and transport properties of Ge1−x−ySnxMnyTe mixed crystals with chemical compositions 0.083≤x≤0.142 and 0.012≤y≤0.119. The transport characterization measurements were performed at temperatures 4.2 1021 cm−3. It was found that the transport properties strongly depend on the chemical composition of the alloy. The magnetic investigations included measurements of linear χ1 and harmonic χ2,3 ac susceptibilities as a function of temperature and of the applied magnetic field amplitude and frequency. Qualitative analysis of our experimental data showed that in the studied system, in the investigated composition range, the spin glass order exists at temperatures up to 50 K.

Based on Mn-doped chalcopyrite ZnSiAs2 the new dilute magnetic semiconductor with p-type conductivity was produced. The Curie temperature behaviour of the produced semiconductor is distinctly dependent on the Mn concentration: 325 K for 1 wt.% and 337 K for 2 wt.% of Mn, consequently. Magnetization, electrical resistance, magnetic resistance and Hall effect of mentioned compositions were studied. Temperature dependence of magnetization M(T) have complicate behaviour. For T ≤ 15 K the M(T) dependence is characteristic for superparamagnetic and at T > 15 K magnetization is sum of magnetizations of ensemble of superparamagnetic clusters and ferromagnetic phase contained frustration regions.