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The magnetic properties of composite alloys of the Cd3As2–MnAs system have been studied as a function of the composition and dimension of the MnAs ferromagnetic phase. Four compositions with the Cd3As2 : MnAs ratio 50 : 50, 60 : 40, 75 : 25, and 80 : 20 mol % have been studied. The 75 : 25 composition corresponded to the eutectic of the Cd3As2–MnAs system. A change in the dimension of the MnAs ferromagnetic phase has been achieved by means of different crystallization rates. The crystallization rate under common conditions was ~0.05 K/s, and the average size of MnAs inclusions in this case was a few micrometers. Under quenching conditions, when salt solutions with high thermal conductivity were used, the crystallization rate reached 90 K/s, which led to the formation of nanosized (≤50 nm) MnAs crystallites. Measurements of the magnetic characteristics of composite alloys showed significant differences between quenched samples and samples prepared under common conditions. The greatest differences are typical of the eutectic composition. The coercive force in it increases eightfold, and the Curie temperature increases by 30 K. The changes in properties are of a singular nature, which is characteristic of the invariant points of phase diagrams, which include the eutectics.

BaFe12O19 nanofilms with uniaxial texture have been synthesized by ion-beam deposition with subsequent annealing. Silicon wafers with sublayers of amorphous alumina (Al2O3), silicon nitride (Si3N4), and their combinations have been used as substrates. The films have been studied by X-ray diffraction and atomic force microscopy. It has been confirmed that hexaferrite with its c axis perpendicular to the plane of the substrate is spontaneously formed on the amorphous surface of Al2O3/Si3N4/Si. The BaFe12O19 films grown on Si3N4 sublayers are characterized by the presence of high strain, leading to the destruction of the ferrite coating after crystallization annealing. The annealed BaFe12O19/Al2O3/Si sample contained additional phases; no signs of the (00l) hexaferrite texture were found.

Textured ZnO films obtained on amorphous substrates using the ion-beam sputtering method are studied. X-ray diffraction and atomic-force microscopy methods show that the resulting films have a polycrystalline structure immediately after deposition. It is established that further annealing of the samples in the temperature range from 200°C to 500°C results in recrystallization, which leads to changes in the grain size and surface roughness. A dependence of the crystallization intensity on the deposition conditions is found, which is related to the number of defects in the unannealed films. In films with an initially more perfect structure, heat treatment at 500°C results in the growth of grains by more than 2 times and a decrease in the roughness by ∼40%.

Permanent magnets constitute an important base for advanced technologies. Rare-earth-based alloys are currently the main permanent magnet materials. Due to the limited availability and high costs, these magnets are, as a rule, used in small items. In large-scale equipment (e.g., in generators, motors, including magnetic levitation transport devices), more affordable and cheaper materials are addressed. Manganese-based alloys, in particular, AlMn, may be regarded as examples of these materials. In Russia, extensive research activity into aluminum–manganese alloys was during the period from the 1960s to the 1990s [1–3]. In other countries this research activity has continued till now. More than one hundred articles were published during the last decade. Most of them address bulk and film samples of the metastable magnetic phase τ-AlMn. Our review focuses on an analysis and systematization of contemporary studies into the preparation and properties of manganese–aluminum alloys; perhaps, it will serve to popularize research into manganese-based intermetallics as promising materials for permanent magnets in Russia.

Semiconductor–ferromagnet alloys in the CdAs2–MnAs system were synthesized in evacuated ampules. Differential thermal analysis (DTA), X-ray powder diffraction analysis, differential scanning calorimetry, and scanning electron microscopy showed that this system is eutectic (of the acicular type), and the coordinates of the eutectic are (6 ± 0.5 mol % MnAs, Tmelt = 614 ± 1°C). The liquidus lines constructed based on the thermal events of melting in DTA are 40–50°C higher than the lines constructed based on the thermal events of crystallization, which is due to the tendency of CdAs2 toward glass transition. The synthesized alloys are ferromagnetic with TC = 315 K, and the magnetization of them increases with increasing MnAs content. The alloys with nanoinclusions ≤40 nm of the ferromagnetic phase MnAs were produced by crystallization from melts at high cooling rates (≤100 deg/s). They have a higher Curie temperature of TC = 353 K and a negative magnetoresistance of ΔR = 2% at 300 K in a saturation magnetic field of 4500 Oe, which is of practical interest for creating magnetic granular spintronic structures.

The pressure dependences of electrical resistance, Hall coefficient, charge carrier mobilities, and magnetoresistance of the Cd3As2–20 mol % MnAs composite are investigated at pressures up to 9 GPa. The pressure dependences of all the listed properties exhibit features related to phase transitions. The presence of pressure-induced negative magnetoresistance is registered. © 2020, Pleiades Publishing, Ltd.

Thin films of Dirac semimetal Cd3As2 about 100 nm thick made of single crystals of cadmium arsenide, prepared by direct fusion of the elements by vacuum–ampoule method, by vacuum–thermal sputtering/depostion have been studied. Temperature and magnetic field dependences of electrical resistance have been measured, which indicate the presence of a superconducting transition at a temperature from 0.2 to 0.6 K.

The Cd3As2+MnAs composite with 20 mole % of MnAs has been studied complexly in a wide ranges of temperatures, pressures and magnetic fields. Negative magnetic resistance has been found in the sample. This anomalous behavior is considered as a result of changes in tunneling processes due to reduce of distance between magnetic moment of ferromagnetic and structural transitions caused by pressure.

Thin films of solid solutions based on the three-dimensional Dirac semimetal Cd3As2 with the addition of manganese are investigated. Cd3 –xMnxAs2 films (x = 0, 0.05, and 0.1) 50–70 nm in thickness are formed on a glassceramic substrate using vacuum-thermal deposition from cadmium arsenide ingots doped by Mn and fabricated by direct alloying elements by the vacuum-cell method. The temperature and magnetic-field dependences of the resistance are measured and the transport parameters of the films under study are determined. Positive magnetoresistance of the characteristic shape corresponding to the contribution of the weak antilocalization effect is observed for films with x = 0 and 0.05. The contribution from the weak localization effect is observed at a higher Mn content (x = 0.1). This change in the quantum correction type as applied to topological semimetals points to reconstruction of the band structure and transition from the Dirac semimetal state into a trivial semiconductor phase, which corresponds to the critical Mn content xc ~ 0.07 in this case.

Thin (~50 nm) cadmium arsenide films have been grown by magnetron sputtering on single-crystal silicon and sapphire substrates. Using X-ray diffraction, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy, the composition of the films has been shown to correspond to the Cd3As2 stoichiometry. Along with the α-Cd3As2 phase, the films contained trace levels of the α'-Cd3As2 phase. Annealing at 520 K led to recrystallization and the formation of [112] textured films on single-crystal silicon substrates. In the annealed films, the crystallite size evaluated using the Debye–Scherrer equation was ~30 nm.

We have studied the effect of hydrostatic pressure on the galvanomagnetic properties of a Cd3As2 + 20 mol % MnAs alloy in a transverse magnetic field of up to 4 kOe. The pressure dependences of the Hall coefficient and resistivity for the alloy provide evidence of reversible phase transitions. The observed negative magnetoresistance of the alloy is shown to be induced by high pressure.

Considerable interest to magnetism of MnAs both in bulk or in the form of epitaxial films is stimulated by its applications as a magnetocaloric material and in spintronic devices. Since the MnAs films deposited on GaAs reproduce well a magnetic transformation related to α– β magnetostructural transition that occurs in bulk MnAs, this first-order phase transition occurs through a phase coexistence over a wide temperature range. Here, we considered the same magnetostructural transition in a bulk hybrid structure based on micrometer-scaled MnAs inclusions embedded into the Cd3As2 matrix. In particular, the effect of high pressure and magnetic fields on the ferromagnetic transition temperature, TC, in a composite Cd3As2 + 30 mol. % MnAs has been studied. We found that at ambient pressure, the transition from α-MnAs to β-MnAs is accompanied by the absence of thermal hysteresis of magnetization, implying a phase coexistence regime. The hysteresis width does not markedly increase even at pressures about P = 0.35 GPa, and displacement of TC occurs with a rate of dTC/ dP ∼ −91.42 K/GPa. In the temperature region of the α– β phase coexistence, a local peak at T = 283 K and P = 1 GPa is observed, which is associated with an antiferromagnetic order of MnAs inclusions. Direct measurements of isothermal magnetization vs pressure indicate both the stabilization of the ferromagnetic hexagonal α phase at P max and the development of an orthorhombic antiferromagnetic long-range order, which propagate up to 5 GPa.

We studied the effect of Mn on the structure and properties of Cd3−xMnxAs2 crystals with x = 0–0.24, synthesized by direct fusion of high-purity elements. Obtained X-ray diffraction patters suggest that the incorporation of Mn promotes a structural phase transition from primary α-Cd3As2 (x = 0) phase to the α''– Cd3As2 (x = 0.24) phase, while at intermediate compositions both phases can coexist. In addition, the increase of Mn content results in the decrease of lattice cell parameters, which effectively saturates for x > 0.13. Microstructural, calorimetric and magnetometry studies suggest that at high Mn content (x = 0.24) secondary MnAs phase appears. Using obtained results, we estimated the solubility limit of Mn in Cd3As2 as x~0.13, which corresponds to the formation of ternary Cd3−xMnxAs2 compound where Cd atoms are partially substituted by Mn. Formation of ternary compound was also suggested by the results for Cd3As2 + MnAs composite systems, where we also observed the presence of CdAs2 phase, which is a byproduct of corresponding reaction. Additional studies suggested that the CdAs2 phase formation in composite system can be prevented if one uses the Cd3−xMnxAs2 compound instead of pure Cd3As2 as a matrix material.

Protocols for sputtering stoichiometric aluminum antimonide thin films were developed by calculating aluminum and antimony vapor condensation flux densities. Aluminum and antimony were sputtered separately. The high chemical reactivity of nanosized aluminum and antimony films made it possible to reduce the synthesis temperature considerably (far below the melting point of the compound). The synthesis involved thermal annealing. The reaction between aluminum and antimony films started at 470°С. Optimal AlSb formation parameters comprise annealing at 540°С for at least 10 h. Film synthesis steps were studied by X-ray powder diffraction, optical, electron, and atomic force microscopy. The composition was monitored by energy dispersive X-ray spectra. The films were found to have hole conductivity; the 300-K charge density and charge mobility in the films are 1 × 1019 cm–3 and 1 × 102 cm2/(V s), respectively.

BaFe12O19 films on Al2O3 (001) substrates were synthesized by ion beam deposition with post-annealing. Three deposition regimes were applied, resulting in unique surface morphology and X-ray diffraction patterns of obtained samples. In the first case, the deposition process was interrupted several times and the sample was subjected to ex situ annealing at 900 °C after each interruption. As a result, a film with high texture degree (about 97 %) was obtained. In the second case, the deposition process was interrupted the same number of times, but during each pause the film remained in the vacuum chamber for 10 min at 300 °C. This approach resulted in a medium texture degree of the sample (about 72 %). In the third case, there were no breaks in the deposition process and the texture of the resulting film was extremely poor. An explanation for the observed differences is proposed. To improve the texture of the films, a second annealing at 1280 °C for 10 h was applied, but as a result strong interdiffusion and misorientation of the grains occurred.

Doping by Mn breaks the time-reversal and crystal symmetry of Cd 3 As 2 , splits Dirac cones and changes band structure. We study these changes using both DFT calculations and magnetotransport measurements. Our band structure of Cd 3 As 2 is confirmed by calculations of dielectric tensor and reflectivity consistent with an experiment. Calculations take into account the n -carrier density of Cd 3 As 2 samples ∼ 1 · 10 18 cm − 3 which shifts the Fermi level by e F ∼ 50 meV. The Mn-doping of Cd 3 As 2 is simulated with the Cd 46 Mn 2 As 32 cell for 9 configurations of Mn atoms. Our simulation shows the preference for antiferromagnetic spin order and tendency towards Mn clustering. Doping by Mn causes transition of Cd 3 As 2 into a trivial topological state with a gap of E g ≈ 40 meV. Our experimental studies of (Cd 1 − x Mn x ) 3 As 2 show that a negative sign of magneto-conductivity is observed at x = 0 and 0.017, but changes to a positive one at x = 0.033 . We argue, this sign change is closely connected with the gap opening and is basically controlled by the ratio E g / e F .

We determined, using a set of physicochemical methods, including X-ray powder diffraction (XRD), differential thermal analysis, and microstructure studies, that the CdAs2–Cd3As2–MnAs ternary system is bounded by three eutectic-type quasi-binary sections: Cd3As2–MnAs, CdAs2–MnAs, and Cd3As2–CdAs2. For Cd3As2–MnAs and CdAs2–MnAs sections, the eutectic coordinates are, respectively, 75 mol % Cd3As2 + 25 mol % MnAs, T m.eut = 604°C; and 92 mol % CdAs2 + 8 mol % MnAs, T m.eut = 608°C. These are rod eutectics. Manganese solubilities in Cd3As2 and CdAs2 phases are insignificant and, according to XRD and SEM, they do not exceed 1 at %. The binary eutectics of the quasi-binary sections form ternary eutectic Cd3As2 + CdAs2 + MnAs, whose average composition as probed by SEM is 34.5 at % Cd, 63 at % Cd and 2.5 at % As and T m.eut = 600°C. Cadmium and manganese arsenide alloys are ferromagnets with the Curie point at ~320 K. The magnetic and electric properties are due to ferromagnetic MnAs microinclusions.

Phase diagram in the ZnSiAs 2 –MnAs nanocomposite system was studied by Х-ray, DTA and SEM. The system has an eutectic character. The coordinates of eutectic are 87±1 mol% MnAs and 847±10 °C. The eutectic consists of the manganese arsenide lattice with ZnSiAs 2 inclusions.

The ZnAs2–MnAs system, characterized by X-ray powder diffraction, differential thermal and microstructure studies, is of the eutectic type, with the coordinates of eutectic 73 mol% ZnAs2 and 27 mol% MnAs and Tm = 716 °C. The solubility of MnAs in ZnAs2 is lower 1 mol%. Alloys of ZnAs2 with MnAs are ferromagnetic with Tc ≈ 318 K, their magnetization being increased with raising the MnAs content.

Barium hexaferrite thin films were prepared by ion beam deposition on sapphire (1 0 2) single crystal substrates. The structural properties of the films were analyzed by means of X-ray diffraction, atomic force microscopy, magnetic force microscopy and scanning electron microscopy. The obtained results were interpreted as a presence of layered structure with different types of texture and its formation mechanism is proposed. The significant influence of BaFe12O19 thickness on its microstructure was observed. Films obtained under certain conditions are potentially fit for further growing of oriented hexaferrite with out-of-plane orientation of c-axis.

Electrical resistivity ρ, Hall factor R H, magnetic resistance (R m–R 0)/R 0, and magnetic-field-dependent resistances were measured in 70 mol % Cd3As2 + 30 mol % MnAs composite at fixed values of high hydrostatic pressures (up to p ≤ 9 GPa). The ρ, R H, and (R m–R 0)/R 0 versus pressure curves feature a phase transition at p = 4–4.3 GPa. Field-dependent magnetic resistance features a negative pressure-induced trend.

Hydrostatic pressure studies of the isothermal magnetization and volume changes up to 7 GPa of magnetic composite containing MnP clusters in an insulating $\mathrm{CdGe}{\mathrm{P}}_{2}$ matrix are presented. Instead of alleged superparamagnetic behavior, a pressure-induced magnetization process was found at zero magnetic field, showing gradual enhancement in a low-field regime up to $H\ensuremath{\geqslant}5$ kOe. The simultaneous application of pressure and magnetic field reconfigures the MnP clusters with antiferromagnetic alignment, followed by onset of a field-induced metamagnetic transition. An unusual hysteresis in magnetization after pressure cycling is observed, which is also enhanced by application of the magnetic field, and indicates reversible metamagnetism of MnP clusters. We relate these effects to the major contribution of structural changes in the composite, where limited volume reduction by 1.8% is observed at $P\ensuremath{\sim}5.2$ GPa.