Type Solid Solution Research Articles

The effect of Al to high-temperature deformation mechanisms and processing maps of Al0.5CoCrFeMnNi high entropy alloy

The high-temperature deformation mechanism and processing maps of cast Al0.5CoCrFeMnNi that comprises face centered cubic (FCC) and body centered cubic (BCC) phases (where BCC phase is a minor phase) were studied at temperatures in the range of 1023–1323 K and at strain rates in the range of 10−3 to 101 s−1. During hot compressive deformation, the hard BCC phase provided nucleation sites for dynamically recrystallized (DRXed) grains in the soft FCC matrix through particle stimulated nucleation (PSN). The PSN-induced DRX occurred by continuous dynamic recrystallization (CDRX) and CDRX accelerated as temperature increased. Due to the effect of PSN, the fraction of DRXed grains was notably higher and the size of the DRXed grain size was considerably smaller in Al0.5CoCrFeMnNi than those in the equiatomic CoCrFeMnNi with a single FCC phase. The effect of the BCC phase on the fraction of DRXed grains was pronounced even at the high strain rate of 10 s-1 in the temperature range between 1173 and 1323 K, which is advantageous for the practical use of cast Al0.5CoCrFeMnNi in the hot-working industry. Solute drag creep appeared at low strain rates and at high temperatures as the rate-controlling deformation mechanism due to the presence of Al solutes in the FCC matrix phase. The activation energy for plastic flow associated with solute drag creep was estimated to be 251 kJ/mol. This value most likely represents the activation energy for the diffusivity of aluminum solutes in Al0.5CoCrFeMnNi. The solute drag creep behavior could be predicted by the Weertman model, suggesting that Al0.5CoCrFeMnNi behaves similar to a typical class I type solid solution metal alloy. By adding aluminum to CoCrFeMnNi, the hot workability can be greatly improved according to the processing maps. The power dissipation efficiency notably increases, and the flow instability regime decreases in size.

Phase equilibria in the Ta–Mn–P system and crystal structure of ternary phosphides, representative of OsGe2-type structure

The phase equilibrium within the Ta–Mn–P system was investigated in the region 0–80 at. % P at T = 1070 K using X-ray powder diffraction analyses. Most of the binary compounds form substitution type solid solutions. Two ternary compounds exist in the Ta–Mn–P system. The earlier known phosphide with TiNiSi-type are formed in the homogeneity region with compositions Ta2.0-xMnxP (x = 0.9–1.25). The crystal structure of the new ternary phosphide Ta1-xMnxP2 (x = 0.09(2)) and isotypical compounds Ta1-xMxP2 (M = V, Fe, Co, Ni, Cu, Zr) have been investigated by X-ray powder diffraction. These compounds crystallize in the OsGe2 type structure. Additional investigations demonstrate that the binary phosphide TaP2 exists at T = 870 K, and at T = 1070 K and 1170 K it decomposes into TaP and P. According DSC data the decomposition of ТаР2 starts at 970(2) K.

Simulation of the NaGd(MoO4)2–NaEu(MoO4)2 and Na2Gd4(MoO4)7–Na2Eu4(MoO4)7 Solid Solutions by the Interatomic Potential Method

Simulation of the solid solutions in the system of double sodium–gadolinium and sodium–europium molybdates, which are promising matrices for solid state lasers and phosphors has been carried out by the method of interatomic potentials. Two types of solid solutions have been studied, one of which contains finite components corresponding to the stoichiometric NaGd(MoO4)2–NaEu(MoO4)2 compositions with statistical distribution of cations in the crystal lattice. Another object is a cation-deficient Na2Gd4(MoO4)7–Na2Eu4(MoO4)7 system, in which we have examined the variants of statistical distribution and partial ordering of cations over structural positions. Atomistic simulation has been performed using the GULP 4.0.1 software package (General Utility Lattice Program). It is shown that when we pass from sodium-gadolinium molybdate to sodium-europium molybdate, both of stoichiometric and cation-deficient compositions, an increase in the unit cell volume is observed, while the density of the crystal, the energy of interatomic interactions in the structure, the vibrational entropy and the heat capacity decrease along with increasing europium content. The energy of interatomic interactions in the structure for cation-deficient solid solutions is less than for stoichiometric ones. Other aforementioned characteristics for cation-deficient solid solutions have greater values than for stoichiometric ones. The role of cluster europium centers in concentration quenching in NaGd(MoO4)2–NaEu(MoO4)2 solid solutions has been examined.

Structural Effects of Magnetostrictive Materials on the Magnetoelectric Response of Particulate CZFO/NKNLS Composites.

In this study, magnetostrictive powders of CoFe2O4 (CFO) and Zn-substituted CoFe2O4 (CZFO, Zn = 0.1, 0.2) were synthesized in order to decrease the optimal dc magnetic field (Hopt.), which is required to obtain a reliable magnetoelectric (ME) voltage in a 3-0 type particulate composite system. The CFO powders were prepared as a reference via a typical solid solution process. In particular, two types of heterogeneous CZFO powders were prepared via a stepwise solid solution process. Porous-CFO and dense-CFO powders were synthesized by calcination in a box furnace without and with pelletizing, respectively. Then, heterogeneous structures of pCZFO and dCZFO powders were prepared by Zn-substitution on calcined powders of porous-CFO and dense-CFO, respectively. Compared to the CFO powders, the heterogeneous pCZFO and dCZFO powders exhibited maximal magnetic susceptibilities (χmax) at lower Hdc values below ±50 Oe and ±10 Oe, respectively. The Zn substitution effect on the Hdc shift was more dominant in dCZFO than in pCZFO. This might be because the Zn ion could not diffuse into the dense-CFO powder, resulting in a more heterogeneous structure inducing an effective exchange-spring effect. As a result, ME composites consisting of 0.948Na0.5K0.5NbO3–0.052LiSbO3 (NKNLS) with CFO, pCZFO, and dCZFO were found to exhibit Hopt. = 966 Oe (NKNLS-CFO), Hopt. = 689–828 Oe (NKNLS-pCZFO), and Hopt. = 458–481 Oe (NKNLS-dCZFO), respectively. The low values of Hopt. below 500 Oe indicate that the structure of magnetostrictive materials should be considered in order to obtain a minimal Hopt. for high feasibility of ME composites.

Phase development in the metastable solid solutions of ZrO2-YO1.5 system

Metastable solid solutions of ZrO2-YO1.5 system (from 0 to 100 mol%) were prepared by crystallization of the amorphous precursors, coprecipitated from aqueous solutions of nitrate salts, using two synthesis routes: hydrothermal treatment at 150 °C for 24 h and annealing in the air atmosphere for 2 h at temperatures between 400 and 1200 °C. Thermal behavior of the amorphous precursors were followed by differential scanning calorimetry (DSC), structural analysis of the crystallization product was performed by X-ray powder diffraction (XRPD) and Raman spectroscopy, and the morphology of the crystalline grains was determined by the scanning electron microscope (FE-SEM). It was found that the crystallization temperature of ZrO2-type solid solutions increase with an increase in the YO1.5 content, from 487 °C (0 mol% of YO1.5) to 516 °C (20 mol% of YO1.5). Comparison of the obtained results with the results obtained for mixed oxides of zirconium with different trivalent dopants indicates that the crystallization temperature rises with the increase of dopand content and the difference between the ionic radius of the zirconium and the doped cation. The results of Rietveld refinements show that, regardless of the significant differences in the crystallite size and the morphology of the products obtained by two different synthesis routes, the phase composition and the unit cell parameters of the solid solutions obtained are very similar and depend mostly on the Zr/Y ratio. Crystallization products with YO1.5 content ≥5 mol% contain only one type of solid solution structurally closely related to tetragonal ZrO2 (from 5 to 15 mol% of YO1.5), cubic ZrO2 (from 15 to more than 60 mol% of YO1.5) and cubic Y2O3 (from 70 to 100 mol% of YO1.5). The unit-cell volume of the ZrO2- and Y2O3-type solid solutions increases linearly with the increase in the fraction of the yttrium. This linear dependence continued even after the transitions from ZrO2-type to Y2O3-type lattice.

Polymorphic Transformation and Magnetic Properties of Rapidly Solidified Fe26.7Co26.7Ni26.7Si8.9B11.0 High-Entropy Alloys.

In this work, the microstructural evolution and magnetic performance of the melt-spun amorphous and amorphous-crystalline Fe26.7Co26.7Ni26.7Si8.9B11.0 high-entropy alloys (HEAs) during crystallization were investigated, respectively. Upon heating fully amorphous ribbons, a metastable BCC supersaturated solid solution together with a little Ni31Si12 crystals first precipitated and then the (Fe,Co)2B crystals formed until the full crystallization was achieved. With further increasing temperature after full crystallization, a polymorphic transformation from a metastable BCC phase to two types of FCC solid solutions occurred. For the amorphous-crystalline HEAs, the dominant crystallization products were the metastable FCC but not BCC crystals. During crystallization, the primary metastable FCC crystals first transform into the metastable BCC crystals and then the newly-generated BCC phase transforms into two types of FCC phases with further increasing temperature. This temperature dependence of the gradual polymorphic transformation results in the change of magnetic properties of the present high-entropy amorphous alloys.

Near-infrared persistent luminescence in Mn4+ doped perovskite type solid solutions

Persistent luminescent phosphors with near-infrared emission have attracted attention in recent years for their promising bio-imaging applications. In the development of persistent materials in the near-infrared wavelengths, Mn4+ is regarded as a promising candidate owing to the 2Eg → 4A2g emission in the deep-red or near-infrared range. In this work, a series of Mn4+ doped perovskite type LaAl1-xGaxO3 and La1-xGdxAlO3 solid solutions with different compositions were successfully prepared using a high temperature solid state reaction method. Mn4+ occupied octahedral positions to substitute Al3+ or Ga3+ in these solid solutions and the 2Eg → 4A2g emission of Mn4+ was tailored by the different local environments of the hosts. Tunable NIR persistent luminescence was achieved by the crystal field control and composition modification. The trap levels of these solid solutions were investigated using thermoluminescence measurements. This kind of perovskite type-based solid solution with tunable near-infrared emission is highly desirable for medical imaging applications.

Examination of B in the Mo solid solution (Moss) in Moss + Mo5SiB2 + Mo2B alloys

During an examination of the Moss (Mo solid solution) + Mo5SiB2 + Mo2B three phase alloys a lattice constant expansion was observed for the Moss. To identify the origin of the expansion, high precision analysis of scanning transmission electron microscopy images was carried out to determine the solid solution type of B atoms. A quantitative analysis of the non-rigid registration image demonstrates that the B is located at the octahedral sites of the Mo lattice. This conclusion is consistent with the expansion of lattice constant and the small solid solubility limit of B in Moss.

Band gap engineering and transport properties of Ba2In2O5: effect of fluorine doping and hydration

Two types of fluorine doped barium indate solid solutions were prepared by a solid state method: Ba2-0.5xIn2O5-xFx (x = 0, 0.1, 0.2) and Ba2In2O5-0.5yFy (y = 0, 0.1, 0.25). Good agreement between the theoretical and experimental values of the pycnometric densities for the studied solid solutions confirms these two distinctly different models of solid solution formation. According to analysis of the XRD data introduction of fluorine ions into the oxygen sublattice of barium indate leads to a decrease in the a lattice parameter and unit cell volume for both types of solid solutions. The effect of fluorine doping and hydration on the band gap of barium indate was studied by means of diffuse reflectance spectroscopy. The estimated value of the band gap width Eg for undoped Ba2In2O5 is 2.94 eV and is in good agreement with literature data. Introduction of fluorine results in a slight increase of Eg and emergence of an additional absorption band in the region of 2.56-2.65 eV, near the fundamental absorption edge, which can be attributed to the -defects appearing upon fluorine doping. The increase of Eg with fluorine introduction correlates well with the decrease of the electronic transport numbers and can be explained by two competing effects: (1) lowering of the top of the valence band due to replacement of O2- ions by F-; and (2) changes in the local structure, i.e., lattice contraction and tilting of the InO(F)x framework. Hydration of the barium indate also leads to an increase of Eg, which was attributed to structural transformation from orthorhombic symmetry to tetragonal. However, with an increase in the fluorine concentration such changes of Eg become less pronounced because of the decrease of the hydration degree due to formation of -defects.

Моделирование твердых растворов NaGd(MoO-=SUB=-4-=/SUB=-)-=SUB=-2-=/SUB=-- NaEu(MoO-=SUB=-4-=/SUB=-)-=SUB=-2-=/SUB=- и Na-=SUB=-2-=/SUB=-Gd-=SUB=-4-=/SUB=-(MoO-=SUB=-4-=/SUB=-)-=SUB=-7-=/SUB=--Na-=SUB=-2-=/SUB=-Eu-=SUB=-4-=/SUB=-(MoO-=SUB=-4-=/SUB=-)-=SUB=-7-=/SUB=- методом межатомных потенциалов

AbstractSimulation of the solid solutions in the system of double sodium–gadolinium and sodium–europium molybdates, which are promising matrices for solid state lasers and phosphors has been carried out by the method of interatomic potentials. Two types of solid solutions have been studied, one of which contains finite components corresponding to the stoichiometric NaGd(MoO_4)_2–NaEu(MoO_4)_2 compositions with statistical distribution of cations in the crystal lattice. Another object is a cation-deficient Na_2Gd_4(MoO_4)_7–Na_2Eu_4(MoO_4)_7 system, in which we have examined the variants of statistical distribution and partial ordering of cations over structural positions. Atomistic simulation has been performed using the GULP 4.0.1 software package (General Utility Lattice Program). It is shown that when we pass from sodium-gadolinium molybdate to sodium-europium molybdate, both of stoichiometric and cation-deficient compositions, an increase in the unit cell volume is observed, while the density of the crystal, the energy of interatomic interactions in the structure, the vibrational entropy and the heat capacity decrease along with increasing europium content. The energy of interatomic interactions in the structure for cation-deficient solid solutions is less than for stoichiometric ones. Other aforementioned characteristics for cation-deficient solid solutions have greater values than for stoichiometric ones. The role of cluster europium centers in concentration quenching in NaGd(MoO_4)_2–NaEu(MoO_4)_2 solid solutions has been examined.

Elaboration, vibrational study and thermal behavior of lacunar apatites NaPb3–xCdxCa(PO4)3 (0 ≤ x ≤ 1)

In this work we are interested in the synthesis of a new solid solution type NaPb3–xCdxCa(PO4)3; (0 ≤ x ≤ 1). The lacunar apatite series are synthesized by a solid-state reaction and studied by X-ray diffraction, infrared and Raman scattering spectroscopy, thermal gravimetric analysis, and differential scanning calorimetry. The crystal structure of these compounds was refined using the Rietveld method. These compounds crystallize in the hexagonal system (space group P63/m) with a number of units per crystal lattice Z = 2. The structure is formed by [PO4]3– tetra­hedra and Pb2+/Ca2+/Cd2+ ions, which constitute the basic skeleton of the structure. The Pb2+/Ca2+/Cd2+ ions occupy the 6h sites, whereas the 4f sites are occupied in half by the Pb2+/Ca2+/Cd2+ ions and the other half by the Na+ ions. The observed frequencies in the Raman and infrared spectra are explained and discussed based on the factor group analysis and by comparison with similar apatites. The vibrational spectroscopy results are in good agreement with the X-ray diffraction measurements. The internal modes of (PO4)3– tetrahedra are assigned and corroborate well with the factor group analysis for the symmetry P63/m. We also investigated the thermal stability of these apatite materials by differential scanning calorimetry.

The effect of cooling rate on the magnetic properties of Cu-Fe-Ni multicomponent alloys with Al and Si additions

The paper explores the structure and magnetic properties of multicomponent high-entropy Al-Cu-Fe-Ni-Si alloys in as-cast and splat-quenched state. This alloy system is characterized by the absence of expensive components, such as Co, V, Mo, Cr, usually used for the production of high-entropy alloys while its characteristics are not inferior to those of more expensive alloys. Components of the studied high-entropy alloys were selected taking into account both criteria for designing and estimating their phase composition, which are available in the literature and based on the calculations of the entropy and enthalpy of mixing, and the difference between atomic radii of components as well. The alloy films were fabricated by a known technique of splat-quenching. A cooling rate estimated by film thickness was ~ 106 K/s. Experimental results reveal that the studied alloys except the Al0.5CuFeNi one are multiphase, with the structure consisting of disordered BCC and FCC solid solutions. The Al0.5CuFeNi alloy has only FCC phase. The leading role in determining the type of solid solution formed in the studied high-entropy films obviously plays an element with the highest melting point. All of the investigated multicomponent films are soft magnetic materials as indicated by low values of coercivity, while most of the as-cast alloys are hard-magnetic.

On the evolution of dislocation cell structures in two Al-alloys (Al-5Mg and Al-11Zn) during reciprocal sliding wear at high homologous temperatures

The formation of dislocation substructures in up to 10 µm deep subsurface regions of two aluminium alloys, Al-5Mg and Al-11Zn, was investigated under conditions of high homologous temperature reciprocal sliding wear (HT-RSW). Under creep conditions, Al-5Mg shows a solid solution type of inverse primary creep. In contrast, Al-11Zn creeps obstacle controlled and exhibits normal primary creep. These two materials were subjected to reciprocal sliding wear at 200 and 300 °C for 100 and 1000 cycles. Flat polished disks were exposed to the 1 mm reciprocal movements of a spherical aluminium oxide counterbody under normal forces of 5 and 10 N at an oscillation frequency of 1 Hz. Using focused ion beam (FIB) micromachining thin electron transparent foils were prepared from the surface regions of the as received and worn material states. Transmission electron microscopy (TEM) was used to study the evolution of nano and micro grain sizes in the surface regions. Despite the different creep behavior, the two materials behave similar under conditions of reciprocal sliding wear. The results obtained in the present work show that subgrain sizes decrease with increasing numbers of wear cycles and increasing normal forces. Subgrain sizes also increase with increasing temperature. At 300 °C, dynamic recrystallization was observed in both Al-alloys. The results of the present work are discussed in the light of previous results reported in the literature. Areas in need of further work are highlighted.

Oxidation and passivating effect in tin(II) fluoride and chloride fluoride solid solutions: a 119Sn Mössbauer study

Divalent tin fluorides and chloride fluorides appear to be stable relative to oxidation to tetravalent tin at ambient temperature. X-ray diffraction shows only the line of the tin(II) compound, however the 119Sn Mossbauer spectrum of all tin(II) polycrystalline samples has a small broad peak at ca. 0 mm/s. This is the case of polycrystalline α −SnF2, while the spectrum of a large single crystal polished sufficiently thin shows only the tin(II) doublet, with no SnO2 peak at 0 mm/s. This shows that there is surface oxidation of each solid particle, to give a thin amorphous layer of SnO2 stannic oxide. However, the Mossbauer peak of SnO2 does not grow with prolonged exposure to air at ambient temperature, therefore it must be assumed that the layer of SnO2 has a passivating effect, however oxidation increases at higher temperatures. We have investigated in this work the passivating effect of a layer of SnO2 in two types of solid solutions: (i) in the fluorite type M1−xSnxF2, where the amount of tin at low x values is not sufficient to provide full coverage of the surface of the particles, and (ii) in the PbClF type doubly disordered solid solution, Ba1−xSnxCl1+yF1−y. It was found that passivation works well in the M1−xSnxF2 solid solution, however most of the time, it does not work so well for Ba1−xSnxCl1+yF1−y where it is strongly dependent on the method of preparation and the bonding strength, as shown by the variation versus the tin(II) recoil-free fraction.

Phase Diagram of the Ternary System NaCl−NaBr−H2O at 348 K

The phase diagram of ternary system NaCl−NaBr−H2O at 348 K was studied by the isothermal equilibrium dissolution method. The solubilities of salts and densities of saturated solutions in the ternary system were determined experimentally. The equilibrium solid phases were also determined by chemical analysis and X-ray powder diffraction. Using the experimental data, the phase diagram of the ternary system was plotted. The diagram comprises one univariant curve and one stationary phase in crystallization filed of Na(Cl,Br).The ternary system was of solid solution type. Density values in the equilibrium solution increase with an increase in the sodium bromide concentration while decrease with an increase of the sodium chloride concentration. Based on the above experimental results, the solid solution compositions can fit well with a quadratic function of the equilibrium liquid composition.

Experimental Observation of the High Pressure Induced Substitutional Solid Solution and Phase Transformation in Sb2S3

The substitutional solid solutions composed of group VA-VIA nonmetallic elements has attracted considerable scientific interest since they provide a pressure-induced route to search for novel types of solid solutions with potential applications. Yet, the pressure-induced solid solution phase is unprecedented in the sulfide family. In this paper, the structural behavior of antimony trisulfide, Sb2S3, has been investigated in order to testify whether or not it can also be driven into the substitutional solid solution phase by high pressures. The experiments were carried out by using a diamond anvil cell and angle dispersive synchrotron X-ray diffraction up to 50.2 GPa at room temperature. The experimental results indicate that Sb2S3 undergoes a series of phase transitions at 5.0, 12.6, 16.9, 21.3, and 28.2 GPa, and develops ultimately into an Sb-S substitutional solid solution, which adopts a body-centered cubic disordered structure. In this structure, the Sb and S atoms are distributed randomly on the bcc lattice sites with space group Im-3m. The structural behavior of Sb2S3 is tentatively assigned by comparison within the A2B3 (A = Sb, Bi; B = Se, Te, S) series under high pressures.

Effects of ZrO2 substitution on crystal structure and microwave dielectric properties of Zn0.15Nb0.3(Ti1-xZrx)0.55O2 ceramics

In this study, the influence of substitution of Zr for Ti on crystal structure and microwave dielectric properties of Zn0.15Nb0.3(Ti1-xZrx)0.55O2 (0 ≤ x ≤ 0.7) ceramics were discussed through Rietveld refinement, normalized bond analysis and complex chemical bond theory. Rietveld refinement analysis indicated that a composite could be formed for x ≤ 0.22. Pure orthorhombic type (O-type) solid solutions are prepared in the region of x = 0.3–0.7. With the increasing amount of ZrO2, cell volume of O-type phase increases, and it results in the enlarging and compressing behaviors of chemical bonds. Under the circumstances, the dielectric polarizability is deteriorated because of the reducing chemical bond covalency value (fc), and this finding is also confirmed by Clausius-Mosotti equation. Lattice energy of Zr–O1 bonds and grain size distribution of sintered specimens are mainly responsible for the variations of quality factor (Q × f) value. Chemical bond energy (E) is closely related with the temperature coefficient of resonant frequency value (τf). Typical microwave dielectric properties of Zn0.15Nb0.3(Ti1-xZrx)0.55O2 ceramics (x = 0.22) were obtained when sintered at 1100 °C: εr = 46.31, Q × f = 30,297 GHz, τf = -8.24 ppm/°C.

Physicochemical Properties of Nanosized Powders of the LaPO4–DyPO4–H2O System

Nanosized La1–xDyxPO4 · nH2O powders are synthesized by the sol-gel method using direct and reverse precipitation. The formation of a continuous series of hexagonal solid solutions based on LaPO4 · nH2O is confirmed by the XRD and DSC/TG methods. A continuous series of monoclinic solid solutions based on LaPO4 is formed at temperatures higher than 600°C. A reflex corresponding to a tetragonal form of DyPO4 is formed during the calcination of DyPO4 powder at 850°C. Two types of solid solutions are observed at temperatures of 1000–1200°C, namely, monoclinic solutions based on LaPO4 (to x ≈ 0.7) and tetragonal solutions based on DyPO4 (0.90 ≤ x ≤ 1.0). The results are compared depending on the methods of nanopowder synthesis.

Effect of aluminum phase in the formation process of thaumasite

ABSTRACTResearch has shown the presence of aluminum phases can accelerate thaumasite formation. This study examines the thaumasite-ettringite solid solutions to investigate the effect of Al phases on the types and morphologies of products, the role of Al phases in the thaumasite formation and attempt to find a new analysis method. The solid solutions were synthesized at 5°C, with Al/Si ratios from 1:9 to 9:1. X-ray diffraction (XRD), scanning electron microscope-energy dispersive spectrometer (SEM+ EDS), X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR) analyses were performed on the 16-week products. Results indicate: two types of solid solutions were formed in all specimens, and their morphologies were related to their elemental compositions and types; the Al phases in ettringites can be replaced by Si to form thaumasite-ettringite solid solutions.

Magnetic Properties of Composite Materials Based on a Solid Solution of Type (CuInSe2)1 – x(MeSe)x (Me = Mn, Fe) and Polyethylene

Basic magnetic characteristics (coercive force Hc, residual magnetization Mr, magnetization M, and saturation magnetization Ms) of solid solutions of type (CuInSe2)1–x(MeSe)x (Me = Mn, Fe) have been investigated in a wide temperature interval (100–300 K). The existence of a magnetic phase transition has been established for all studied solid solutions at low temperatures, and the Neel temperatures have been determined from the temperature dependences of the magnetization. It is shown that the temperature dependences of coercive force Hc and of magnetization M can be described using the thermal relaxation (fluctuation) theory.