The direct measurements of the adiabatic temperature change under cyclic conditions have been carried out for Fe48Rh52 alloys obtained by different heat treatment protocols. Furthermore, the magnetocaloric long-term performance has been estimated. The results demonstrate that the degradation of the magnetocaloric properties observed in FeRh can depend on the microstructure of the alloys. Besides, the selection of the cycling temperature can affect the performance as well. The magnetic measurements carried out after the cyclic experiment revealed a shift of the transition towards lower temperatures, which can be correlated to the possible stress that was accumulated during the repetitive magnetostructural transition. Then, it has been shown that the degraded material can be healed by a low temperature annealing those results in the recovery of the magnetostructural transition. The outcome can give a hint for the efficient design of magnetocaloric alloys and the selection of the working temperature in order to diminish the degradation effects.

The effect of titanium or niobium disulfides doping of iron telluride has been studied for the first time by means of x-ray diffraction analysis, electrical resistivity and magnetization measurements. It has been revealed that an increase in the dopant content in the Fe1.1Te(TS2)(y) (T = Ti, Nb) systems (y = 0, 0.04, 0.08, 0.1, 0.2) is accompanied by the additional phase separation and leads to a decrease in the crystal lattice parameters of the tetragonal phase, partial suppression of antiferromagnetic ordering and an appearance of superconductivity. In doped samples a transition to the superconducting state has been detected upon cooling below T-c(onset) similar to 9 K coexisting with antiferromagnetism. Superconductivity is suggested to exhibit a granular character due to inhomogeneity of the samples and the small volume fraction of superconducting phase. The difference in the superconducting transitions for both dopant types may be associated with different morphologies and compositions of resulting phases.

An Erratum to this paper has been published: https://doi.org/10.1134/S0031918X24120032

FeRh-based alloys are unique objects, the study of which allows us to identify new features of first-order magnetic phase transitions. Doping of an alloy often leads to significant changes in its magnetic properties. This paper examines the structural, magnetic, transport and caloric properties of iron-rhodium alloys with different cobalt doping with varying cobalt content (0-1.8 at%). Doping the alloy with less than 2 at% cobalt resulted in a decrease in the phase transition temperature by 200 K. Based on the results obtained, a relationship was established between the magnetic properties and the heterogeneity of the elemental composition of the samples. It was also demonstrated that significant changes in the parameters of the magnetic phase transition of the alloy upon alloying are largely determined by the electronic properties. Considering the sensitivity of the alloy properties to the cobalt content, we develop a novel methodology for quantifying local compositional variations using temperature-dependent measurements, demonstrating its superior sensitivity compared to conventional techniques. The strong correlation between magnetocaloric response and cobalt concentration highlights the importance of precise composition control for applications.

Using the modified Bridgman method, a single-crystalline sample of iron selenide Fe3Se4 was grown and its magnetization and thermal expansion behavior was studied along different crystallographic directions. In a ferrimagnetically ordered state below T N = 345 K, the magnetization curves show that the magnetic moments do not lie strictly in the plane perpendicular to the c axis. The magnetocrystalline anisotropy constants, determined from the M ( H ) dependences along and across to the c axis, are K 1 =- 3.9.107 erg/cm3, K 2 = 5.0.106 erg/cm3 at 4 K. Magnetic ordering in Fe3Se4 upon cooling below T N is accompanied by anisotropic deformations of the crystal lattice: expansion along the c axis and compression across the c axis. Spontaneous volume magnetostriction is positive and reaches a giant value of about 1.2.10- 2 at 80 K. The pressure derivative of the Neel temperature is estimated using the Ehrenfest ratio as of dTN/dp approximate to- 2.1 K/kbar. The results obtained show that the properties of Fe3Se4 are strongly influenced by magnetoelastic interactions.

For the first time, an 93Nb NMR study of dichalcogenides CrxNbSe2 (x = 0.33, 0.5) in the paramagnetic state was performed. Analysis of the 93Nb NMR spectra revealed the presence in CrxNbSe2 of three magnetically nonequivalent niobium positions, whose immediate environment contains 0, 1, and 2 chromium ions, respectively. For each Nb position with a different number of chromium atoms in the immediate environment in CrxNbSe2 (x = 0.33, 0.5), the values of the components of the magnetic shift and electric field gradient tensors at the position of the niobium nuclei were determined. Evidence was obtained of the formation in Cr0.33NbSe2 of the ordering of chromium ion positions in the ab plane into a √(3) a0 × √(3) a0 superstructure. On the other hand, in Cr0.5NbSe2, no obvious indications of the formation of any superstructure of chromium ion positions were found. It has been established that the overlap of the 4d and 5s shells of niobium ions and the 3d orbitals of chromium leads to the appearance of a positive hyperfine field induced by the magnetic moments of chromium on Nb nuclei. From the temperature dependences of the shift and susceptibility in Cr0.5NbSe2, an estimate of these induced hyperfine fields is made.

We suggest an explanation based on the Blume-Capel model of why some layered compounds of the iron-intercalated transition metal dichalcogenides TaS2(Se2) exhibit spin-glass behavior, while another group of this family demonstrates low-temperature paramagnetism. In these materials, the doped Fe atoms either substitute the Ta atoms with losing their magnetic moments or sit between the TaS2(Se2) layers keeping their spin states. The Blume-Capel model allows us to introduce a chemical potential to control a balance of the intercalated elements of both types. The Ghatak-Sherrington theory of spin-glass behavior of this model predicts an existence of a tricritical point that means that there is a concentration threshold of Fe ions retaining their magnetic moments, above which spin-glass ordering occurs. Below the threshold, Fe ions behave as independent paramagnetic centers. We build temperature dependencies of magnetic susceptibility and field dependencies of magnetization to highlight specific features of the model related with a variable content of Fe ions in the high-spin state. A specific crystal structure of the layered transition metal dichalcogenides gives an opportunity to increase the concentration of ions with nonzero magnetic moments by co-intercalating non-Kramers 3d ions into the van der Waals gaps. This process may trigger spin-glass ordering in the initially paramagnetic Fe-doped TaS2(Se2) polytype complexes.

The Fe0.25TaSe2 polycrystalline samples have been synthesized using two routes of solid-state reactions and various heat treatments and cooling conditions. The obtained samples have been studied by x-ray diffraction, magnetization and electrical resistivity measurements. It has been revealed that various methods of preparation and heat treatment do not have a strong effect on the lattice parameters of the main phase in the samples, but they significantly affect the magnetic critical temperature and magnetic hysteresis of the samples. Depending on the sample preparation procedure magnetic ordering temperature of Fe0.25TaSe2 is observed to vary in the range 33-60 K. The coercive field values from 31.7 kOe to 65.3 kOe at T = 2 K are indicative of a very high magnetocrystalline anisotropy in this material. The observed distinctions in the magnetic characteristics of the Fe0.25TaSe2 samples obtained by various methods and after different heat treatments can be ascribed to the difference in the distribution of Fe atoms over the crystal lattice.

The properties of the selenide compound Fe7Se8 with a layered crystal structure of the NiAs type are strongly influenced by substitutions and the distribution of vacancies. The Cr-substituted compound Fe6.5Cr0.5Se8 was obtained in single-crystalline form and studied by x-ray diffraction, energy-dispersive x-ray spectroscopy, thermal expansion and magnetization measurements. It was observed that the partial replacement of iron with chromium led to a twofold decrease in spontaneous volume magnetostriction due to changes in competing magnetoelastic contributions to thermal expansion along and perpendicular to the c axis of the crystal. The replacement of iron with chromium slightly decreases the N & eacute;el temperature (from 440 to 435 K) and significantly enhances the critical temperature of spin reorientation transition T-sr (from 115 to 160 K), apparently due to a change in the crystal electric field. Below 160 K, the Fe6.5Cr0.5Se crystal is found to exhibit metamagnetic-like behavior of the magnetization when the magnetic field is applied along the c axis. A jump-like change of the magnetization at a critical field up to similar to 10 kOe is attributed to the presence of pinning centers of domain walls presumably due the ordering of chromium atoms substituting iron in cationic layers.

The researches of the structural and magnetic properties of the layered chalcogenide Fe4Co3Se8, which has a ferrimagnetic order below T = 196 K, have been performed by means of X-ray diffraction, magnetic susceptibility measurements, and 59Co nuclear magnetic resonance (NMR) spectroscopy. It is found that the effective magnetic moment of iron ions is μeff ≈ 5.90(5) μB. The components of the magnetic shift and electric field gradient tensors at the Co nuclei sites have been determined. The hyperfine field induced on Co nuclei from neighboring iron ions has been estimated from the temperature dependences of the shift and susceptibility in Fe4Co3Se8. It was also established that cobalt ions in Fe4Co3Se8, as well as in the Co7Se8 compound, do not have intrinsic magnetic moment, but they do have a moment induced from neighboring iron ions μ _eff^Co ≈ 0.36(4) μB, which decreases at the magnetic ordering to 0.07(1)μB due to mutual compensation of contributions from neighboring iron ions.

Using the solid-phase method, a series of layered compounds Fe0.25TaS2-ySey has been synthesized and studied using X-ray diffraction, magnetization, electrical resistivity and magnetoresistance measurements to reveal the evolution of the crystal structure and properties with the replacement of sulfur by selenium. The crystal structure of Fe0.25TaS2-ySey consists of chains along the c axis, in which tantalum and iron atoms alternate in trigonalprismatic and trigonal-antiprismatic coordination, respectively. The replacement of sulfur by selenium is accompanied by an anisotropic expansion of the crystal and a relative elongation of the structure in the direction perpendicular to the plane of the layers. All the Fe0.25TaS2-ySey compounds exhibit ferromagnetic behavior with a huge coercive field (Plc - 40-60 kOe at low temperatures) which decreases exponentially with increasing temperature. It is assumed that an almost twofold decrease in the value of TC (from 120 K to - 60 K) when sulfur is replaced by selenium occurs mainly due to a decrease in the polarization of the 5d electrons of tantalum, through which an indirect exchange interaction between the 3d electrons of Fe occurs. The change of the lowtemperature (2 K) coercive field with the Se for S substitution is found to correlate with the concentration dependence of the Curie temperature, which is indicative of the Ising spin state of Fe ions in these compounds.

Polycrystalline samples of the Fe2CrSe4 compound have been synthesized and studied by means of x-ray diffraction and magnetization measurements. The as-synthesized Fe2CrSe4 sample shows ferrimagnetic ordering below TN -300 K with a compensation point Tcomp -140 K. This compound is found to exhibit a large coercive field (half-width of the hysteresis loop reaches 15 kOe at 2 K) and a significant exchange bias (EB) effect below 50 K (HEB up to 6.6 kOe) after cooling in an applied field and after zero-field cooling. The exchange bias in Fe2CrSe4 is suggested to result from the presence of regions (clusters) with short-range correlations in the ferrimagnetic matrix due to the inhomogeneous distribution of iron and chromium atoms over the lattice. Additional heat treatment and subsequent rapid cooling lead to an increase in magnetic ordering temperature, the disappearance of compensation for sublattice magnetizations and a decrease in the exchange bias, thus showing the possibility of controlling the exchange bias and magnetic characteristics in the system.

This paper presents the results of measuring the structural, magnetic, and caloric properties of the (Fe,Ru)Rh alloy. This compound has demonstrated a new record of the reversible magnetocaloric effect ( |Δ T|_ad under cycling = 7.1 K for B = 1.95 T ). We provide a classification of the results for the family of FeRh-based compounds. The analysis of these results allows us to put forward the mechanisms that lead to a change in the magnetocaloric effect value at low doping.

Temperature and field-dependent neutron powder diffraction (NPD) measurements have been performed to reveal the nature of the unusual evolution of the magnetoresistance behavior with increasing Fe content in the intercalated compounds FexTiS2 (with x = 0.25, 0.33, 0.50, 0.55) synthesized by solid-phase reaction method with prolonged homogenization heat treatment. As derived from neutron diffraction measurements, both the Fe0.25TiS2 and the Fe0.50TiS2 compound exhibit an antiferromagnetic (AFM) order below their respective Neel temperatures T-N approximate to 52 K and T-N approximate to 140 K, which results in the presence of a large magnetoresistance accompanying the field-induced phase transition from AFM to the ferromagnetic (FM) state. At low temperatures, this AFM-FM transition is irreversible, confirmed by the irreversibility of changes in the NPD patterns and the presence of remnant magnetoresistance. In contrast, Fe0.33TiS2 shows short-range magnetic order at T-f approximate to 44 K due to a triangular network of intercalated Fe atoms and frustrations of exchange interactions with a field-induced FM alignment of Fe magnetic moments in an applied magnetic field as revealed by NPD measurements. The field-induced transformations of the cluster glass magnetic state in this compound lead to a significant decrease in electrical resistivity. According to NPD data, a reduced impact of an external magnetic field on the electrical resistivity of the compound Fe0.55TiS2 can be ascribed to the presence of ferromagnetic or ferrimagnetic order in compounds with the Fe concentrations above x = 0.50. The results obtained indicate that the distribution of the Fe atoms, along with their concentration in FexTiS2 layered compounds, plays a decisive role in the formation of the magnetic state and the behavior of the magnetoresistance.

Magnetic phase transitions in alloys are highly influenced by the sample preparation techniques. In the present research, electronic and magnetic properties of Fe48Cr3Rh49 alloys with varying cooling rates were studied, both experimentally and theoretically. The degree of crystalline ordering was found to depend on the cooling rate employed after annealing the alloy. Modeling of alloy structures with different degrees of crystalline ordering was carried out via strategic selection of substitution positions and distances between chromium atoms. Theoretical calculations revealed significant changes in magnetic and electronic properties of the alloy with different substitutions. A comprehensive analysis of the calculated and experimental data established correlations between structural characteristics and parameters governing the magnetic phase transition. In this study, we also developed a method for evaluating the magnetic properties of the alloys obtained under different heat treatments. The proposed approach integrates atom substitution and heat treatment parameters, offering precise control over alloy manufacturing to effectively tune their essential magnetic properties.

Specific heat, thermal expansion and magnetic measurements on single crystalline samples have been employed to study the interplay between the lattice and the magnetic state in the layered iron selenide compound Fe7Se8, which exhibits a ferrimagnetic order below T-N approximate to 440 K and a spin reorientation transition upon cooling below T-sr similar to 115 K. Thermal expansion measurements performed on single-crystal samples revealed significant anisotropic deformations of the crystal lattice with decreasing temperature below T-N, an increase in the c/a ratio, and negative volume spontaneous magnetostriction (omega(s) similar to -5.3 center dot 10 (-3) at 120 K). The first-order spin reorientation transition in Fe7Se8 is found to be accompanied by a hysteretic behavior of the specific heat and thermal expansion, and an anomaly in the omega(s) vs T dependence. The results obtained are indicative of a strong influence of the magnetoelastic interactions on the properties of Fe7Se8.