Institute of Physics. HI Amirkhanova

The Ni45Mn36In14Co5 alloy was produced by the argon arc melting method. The application of a homogenization annealing process at 1173 K, followed by water quenching, resulted in the formation of a practically single-phase state. This particular state is referred to as the initial state. In the region of the structural transition, an abrupt change in magnetization is observed as the austenitic ferromagnetic phase transitions to the weakly magnetic martensitic phase. The magnetic entropy of ∆SM = -31.9 J/kg·K was obtained from thermomagnetic data in a magnetic field of 3 T. The reversible magnetocaloric effect ∆Tad = -0.7 K was observed in an alternating f = 0.2 Hz magnetic field of 1.8 T at the peak of the martensitic transformation. The maximum value observed during the initial application of the magnetic field is ∆Tad = -2.5 K. A study of the degradation of the magnetocaloric effect at the martensitic transformation temperature indicates that following 1400 cycles of magnetic field application, the ∆Tad value exhibits a 10% reduction, with a discernible ongoing trend. In conclusion, the alloy displays notable magnetocaloric effect values.

Direct measurements of the adiabatic temperature change ∆ T ad depending on the temperature and frequency of magnetic field changes in the Ni45.37Mn40.91In13.72 Heusler alloy were carried out. The dependence of the magnetocaloric effect (MCE) on frequency in this alloy is anomalous: the MCE decreases with frequency more strongly in the region of the magnetic phase transition than in the region of the magnetostructural phase transition. A universal curve of adiabatic temperature change in magnetic fields of different frequencies is proposed, which shows that there is a deviation from the universal behavior at frequencies of 30 Hz, which can be explained by the thermal inertia of the thermocouple. Using such a phenomenological universal curve, experimental results can be extrapolated to magnetic field frequencies that are inaccessible in the laboratory or frequencies at which it is impossible to measure using known techniques.

A model of a “smart” composite based on a thermosensitive PNIPAM polymer deposited on a FeRh substrate with a modified periodic microstructure was proposed. The initial parameters of the model were determined from the properties of the actual composite sample and its components. Cooling of the sample using a magnetic field was shown by two independent methods, and at ~37 °C, it was −5.5 °C when a magnetic field of 1.8 T was applied. Based on experimental data, models of traditional and modified PNIPAM/FeRh composites were constructed. Calculations show that surface modification allows for an increase in the activation time for a polymer layer that is 20 µm thick from ~20 ms for a conventional composite to ~60 ms for a modified composite. Modification of the surface in the form of wells can be used to more effectively implement the idea of loading and releasing drugs for potential biomedical applications.

Based on the replica exchange algorithm of the Monte Carlo method, the influence of an external magnetic field on phase transitions and thermodynamic properties of the two-dimensional antiferromagnetic Potts model with the number of spin states q = 4 on a hexagonal lattice was studied. The studies were conducted in the range of external magnetic field values of 0.0 ≤ h ≤ 10.0. The magnetic field is measured in relative units of exchange interaction between nearest neighbors |J1|. The magnetic structures of the ground state were obtained, and the nature of phase transitions in the considered field range was analyzed. It has been established that in the intervals 0.0 ≤ h ≤ 3.0 and 6.0 ≤ h ≤ 6.5 a first-order phase transition is observed. It is shown that at the external magnetic field values h = 3.5 and 5.5, the system is frustrated, and in the magnetic field intervals 4.0 ≤ h ≤ 5.0 and 7.0 ≤ h ≤ 8.5, the system approaches the frustration regime. It was found that strong magnetic fields (h ≥ 9.0) suppress the phase transition in the system.

The process of high-temperature oxidation of silicon carbide-based ceramic materials synthesized by spark plasma sintering without any sintering-activating additives has been studied. Analysis of the microstructure of the oxidized ceramic samples and the data on the change in their mass indicate the formation of a protective SiO 2 layer on the SiC surface, which is characteristic of passive oxidation of silicon-containing oxygen-free compounds. The results of the comparative study of oxidation of the SiC ceramic samples with different porosity in air at a temperature of 1200°C have revealed a linear relationship between the growth rate of the oxidized sample mass and the volume of open pores in the sample.

The results of direct measurements for the adiabatic temperature change ΔTad in the Ni47Mn40Sn13 alloy in cyclic magnetic fields by the magnetic field modulation method are presented. In the temperature dependence of the magnetocaloric effect (MCE), direct (ΔTad > 0) and inverse (ΔTad < 0) MCE are detected. The inverse effect value in a cyclic magnetic field depends on the temperature scanning rate. An increase in the frequency of a cyclic magnetic field with an induction of 1.2 T from 1 to 30 Hz decreases the direct effect value by more than 2 times. In a cyclic magnetic field with an induction of 1.2 T at frequencies f ≥ 1 Hz, complete disappearance (“collapse”) is observed for the inverse magnetocaloric effect, while ΔТad during the one-time actuation of magnetic field is –0.49 K. The dependence of the inverse effect value on the temperature scanning rate, along with its strong frequency dependence, results from both the manifestation of irreversibility in the magnetostructural phase transition due to hysteresis and the presence of phase inhomogeneities influencing the phase transition kinetics.

An Erratum to this paper has been published: https://doi.org/10.1134/S0031918X24110012

The possibility observation of the electric field controlled multicaloric response through quasi-isostatic compression as a result of the converse piezoelectric effect was demonstrated on the cylindrical type magnetoelectric composite MnAs/PZT. It was shown that an electric voltage of 100 V corresponding to an electric field of E ∼0.3 kV/mm applied to the walls of the piezoelectric component PZT of the MnAs/PZT composite contributes to an increase in the maximum adiabatic temperature change by 0.2 K in the temperature range of the magnetostructural phase transition of MnAs ∼317 K at a magnetic field change of 1.8 T. Numerical analysis using the finite element method has shown that an electric field voltage of 100 V is capable of creating a quasi-isostatic mechanical stress in the region inside a cylindrical PZT tube of ∼3 MPa. Moreover, in the region of weak pressures up to 10 MPa, the contribution to the total adiabatic temperature change from piezo-mechanical compression linearly depends on the electrical voltage that can be used for control by magnetic and caloric properties of multicaloric materials.