S. F. Marenkin

Effect of Hydrostatic Pressure on the Transport Properties of Cadmium Diarsenide Crystals

The electrical resistivity and Hall coefficient of n-type CdAs2crystals cut along [001] and [100] were measured at hydrostatic pressures in the range 0–9 GPa. The ρ(P) and RH(P) curves for the [001] direction show three peaks at 1.8, 3, and 5.5 GPa. In the [100] direction, the curves show two peaks at 3 and 5.5 GPa. The peaks at 1.8 and 3 GPa are likely related to impurity levels. The peak at 5.5 GPa is due to the phase transition of CdAs2 . The parameters of the phase transition are determined.

Manufacture of magnetic granular structures in semiconductor-ferromagnet systems

The requirements are formulated to be fulfilled by magnetic granular structures that have the giant magnetoresistance (GMR) in semiconductor-ferromagnet systems. AIIBIVC2V-Mn(CV), AIIICV-Mn(CV), and A3IIC2V-Mn(CV) semiconductor-ferromagnet systems are shown to be eutectic systems and to be promising for the preparation of granular structures with high magnetoresistance values. Magnetic granular structures have been prepared in Zn(Cd)GeAs2-MnP(As), Zn(Cd)3P(As)2-MnP(As), and (Al,Ga,In)Sb-MnSb systems and the origin of magnetoresistance in these systems is shown to be due to the structure of Mn(CV) ferromagnet clusters.

Ferromagnetism of manganese-doped InSb alloys

InSb samples containing 0.22–1.42 wt % manganese were synthesized and identified. The unit cell parameter decreased as the manganese concentration increased. The samples contained microinclusions of manganese antimonides. Electrical and magnetic measurements showed two ferromagnetic phases (In1−xMnxSb solid solution with Tc ∼ 7 K and MnSb with Tc ∼ 580 K) and a ferrimagnetic phase (Mn2Sb). The samples had p-type conductivity with a charge carrier concentration of about 1020cm−3. The semiconductor conductivity was observed at low temperatures and changed to the metal conductivity with temperature elevation.

New ferromagnetics based on manganese-alloyed chalcopyrites AIIBIVC2V

This review describes the principles of semiconductor spintronics, represents the physicochemical properties of materials based on manganese-alloyed AIIBIVC2V compounds, considers the results from theoretical simulation of magnetic properties of AIIBIVC2V alloyed with 3d metals, summarizes the basic approaches to explanation of ferromagnetism with Curie points above room temperature arising in AIIBIVC2V:Mn, and indicates promising ways to synthesize and study magnetic semiconductors based on chalcopyrites AIIBIVC2V in order to produce a suitable material for spintronic devices.

Growth of magnetic eutectic GaSb-MnSb films by pulsed laser deposition

Eutectic GaSb + MnSb films ranging in thickness from 80 to 130 nm have been grown on sapphire substrates by pulsed laser deposition using mechanical droplet separation. The films were similar in composition to the ablation target, consisting of the eutectic GaSb-MnSb alloy. According to atomic force and electron microscopy data, the films were homogeneous, with p-type conductivity. Their electrical properties depended significantly on deposition conditions. The best films had a resistivity of 7 × 10−3 Ω cm, carrier concentration of 8.1 × 1019 cm−3, and carrier mobility of 102 cm2/(V s). Characteristically, the films had a negative magnetoresistance. Their magnetization curves showed saturation in a magnetic field of ∼1 × 10−1 T. According to the magnetic-field dependences, the coercive force in the films was within 3 × 10−2 T; that is, the films were soft magnets with a small domain size.

Physicochemical foundations of synthesis of new ferromagnets from chalcopyrites AIIBIVC2V

The results of studying phase equilibria of ternary AIIBIVCV systems have been reported. Physicochemical foundations have been developed for the synthesis of new ferromagnets with Curie temperatures above room temperature structurally compatible with basic semiconducting materials. Methods of synthesis and physicochemical properties of manganese-doped AIIBIVC2V ferromagnets have been described. The results of theoretical simulation of magnetic properties have been considered and basic approaches to the explanation of the emergence of ferromagnetism in AIIBIVC2V doped with 3d metals have been surveyed. The most promising ways to produce and study dilute magnetic semiconductors as spintronics materials have been presented.

Magnetic and electrical properties of the ZnGeAs(2): Mn chalcopyrite

Doping of the ZnGeAs2 semiconductor with manganese has produced compositions with spontaneous magnetization and high Curie temperatures of up to 367 K for the composition 3.5 wt% Mn. Their magnetic properties are characteristic of spin glasses at temperatures T < TS and magnetic fields H < 11 kOe. In stronger fields, the spin glass state transforms into a phase with a spontaneous magnetization 4–5 times weaker than that to be expected under ferromagnetic ordering of all Mn ions. This is obviously a singly-connected ferromagnetic phase containing regions with frustrated bonds. The frustrated regions and the spin glass phase have inclusions of noninteracting ferromagnetic clusters, because these regions and the spin glass phase at low temperatures exhibit a strong increase in the magnetization M, with the dependence M(T) being described by the Langevin function. Measurements of the electrical resistivity ρ and the Hall effect have revealed that, for T < 30 K, the resistivity ρ of compositions with 1.5 and 3.5 wt % Mn is higher that at 30 K, which makes superexchange dominant and gives rise to the onset of the spin glass state. The nonuniform distribution of Mn ions in the spin glass phase accounts for the existence of isolated ferromagnetic clusters, their ferromagnetism being generated by carrier-mediated exchange. As the temperature increases still more, the increase in the mobility occurs faster than the decrease in the concentration, thus promoting an enhancement of the carrier-mediated exchange and growth of the ferromagnetic clusters in size, which at T = TS come in contact. This signifies a transition from a multiply-to a singly-connected ferromagnetic phase, which contains microregions with frustrated bonds.

A new High-Tc ferromagnet: Manganese-doped CdGeAs2 chalcopyrite

New ferromagnets with high Curie temperatures, reaching 355 K, have been obtained by doping a GdGeAs2 semiconductor compound with manganese. The obtained compounds are magnetically inhomogeneous, comprising a mixture of ferromagnetic (FM) and paramagnetic phases. The volume fraction of the FM phase increases with the degree of doping. The development of ferromagnetism in this system is probably related to the presence of vacancies of the (Cd, VC, Mn)GeAs2 type or to a nonstoichiometry of the (Cd, Ge, Mn)GeAs2 type, since theoretical estimates show that the FM state is energetically more favorable than the spin glass state only in these cases.

Manganese-doped ZnSiAs2 chalcopyrite: A new advanced material for spintronics

A new spintronics material with the Curie temperature above room temperature, the ZnSiAs2 chalcopyrite doped with 1 and 2 wt % Mn, is synthesized. The magnetization, electrical resistivity, magnetoresistance, and the Hall effect of these compositions are studied. The temperature dependence of the electrical resistivity follows a semiconducting pattern with an activation energy of 0.12–0.38 eV (in the temperature range 124 K ≤ T ≤ 263 K for both compositions). The hole mobility and concentration are 1.33, 2.13 cm2/V s and 2.2 × 1016, 8 × 1016 cm−3 at T = 293 K for the 1 and 2 wt % Mn compositions, respectively. The magnetoresistance of both compositions, including the region of the Curie point, does not exceed 0.4%. The temperature dependence of the magnetization M(T) of both compositions exhibits a complicated character; indeed, for T ≤ 15 K, it is characteristic of superparamagnets, while for T > 15 K, spontaneous magnetization appears which correspond to a decreased magnetic moment per formula unit as compared to that which would be observed upon complete ferromagnetic ordering of Mn2+ spins or antiferromagnetic ordering of spins of the Mn2+ and Mn3+ ions. Thus, for T > 15 K, it is a frustrated ferro- or ferrimagnet. It is found that, unlike the conventional superparamagnets, the cluster moment μc in these compositions depends on the magnetic field: ∼12000–20000μB for H = 0.1 kOe, ∼52–55μB for H = 11 kOe, and ∼8.6–11.0μB at H = 50 kOe for the compositions with 1 and 2 wt % Mn, respectively. The specific features of the magnetic properties are explained by the competition between the carrier-mediated exchange and superexchange interactions.

Synthesis and magnetic properties of the InSb-MnSb eutectic

It has been demonstrated by a combination of physical and chemical methods that InSb and MnSb form an eutectic (6.5 mol % MnSb, Tm = 513°C). A composition consisting of a [110] oriented InSb single crystal matrix and faceted single-crystal MnSb inclusions has been grown by the Bridgman method. The composition shows pronounced electrical conductivity anisotropy. The electrical conductivity along needle-like MnSb inclusions is 5 times higher than the electrical conductivity in the perpendicular direction. The composition possesses magnetic properties and has a Curie temperature of ∼600 K. The material is of interest as a substrate for ferromagnet/semiconductor heterostructures.