Physics of the Solid State, 2023, Vol. 65, No. 6 01,05,13 Magnetocaloric effect of FeNi magnetic nanoparticles obtained by the electrical explosion of wire technique © G.V. Kurlyandskaya 1 , A.V. Arkhipov 1 , I.V. Beketov 1,2 , A.V. Bagazeev 2 , A.S. Volegov 1 , A. Larra ˜ nanga 3 , E.A. Mikhnevich 1 , A.V. Svalov 1 1 Institute of Natural Sciences and Mathematics, Ural Federal University named after the First President of Russia B.N. Yeltsin, Yekaterinburg, Russia 3 The Basque Country University UPV-EHU, Bilbao, Spain E-mail: galinakurlyandskaya@urfu.ru Received April 17, 2023 Revised April 17, 2023 Accepted May 11, 2023 In this work the structure, magnetic properties and of the magnetocaloric effect of the large batches of magnetic FeNi nanoparticles were studied for selected compositions close to the invar. Nanoparticles were synthesized by the method of the electric explosion of wire using various technological parameters ensuring the difference in their dispersion parameters. The main variable parameter was the degree of overheating of the wire material. The use of different technological conditions for obtaining batches of nanoparticles ensured the difference in their dispersion parameters. Keywords: electric explosion of wire, magnetic nanoparticles, invar composition, magnetic properties, magnetocaloric effect. DOI: 10.21883/PSS.2023.06.56092.25H 1. Introduction Magnetic cooling technology is now regarded as a promis- ing, efficient counterpart to modern compression cooling. It is based on the magnetocaloric effect (MCE)— the ability of magnetic materials to change their temperature under the influence of an external magnetic field [1]. The maximum value of the MCE is achieved near the phase transitions observed in the working magnetic material. The highest MCE is observed in materials which characterized by a phase transition of the first kind, with a relatively narrow temperature range; these materials are also characterized by hysteresis phenomena. For materials in which a magnetic phase transition of the second order is observed, the magnetocaloric peak is smaller, but the width of the temperature interval at which this peak is observed is much greater than in materials with a magnetic phase transition of the first order [2]. This increases the so-called relative cooling power (RCP) or cooling capacity, the value of which is defined as the product of the maximum magnitude of the peak change in the magnetic portion of the entropy (S M(max) (T , H )) and the width of this peak at half its height (δ T FWHM )[3]. Among the materials exhibiting magnetic phase transition of the second kind, gadolinium remains the most popular in terms of working material for the ” magnetic cooler“ due to its large MCE value and proximity of the Curie temperature to room temperature [3–5]. Transition metal alloys have a markedly lower MCE, but their advantages are high me- chanical strength, corrosion resistance, negligible magnetic hysteresis, easily varied Curie temperature, including in the temperature range above room values, which makes them a promising material for multistage magnetic cooling systems starting from temperatures above room temperature [2,6]. The task of improving the efficiency of heat transfer between the working body and the environment requires the use of magnetic materials for magnetic cooling devices in various forms, including in the form of powders and stabilized suspensions based on them [7–9]. The most common method of producing magnetocaloric powders is the ball mill method [7,9]. In recent years, the electrophysical method of electric explosion of the wire (EEW) has become widespread for obtaining very large batches of powders, making it possible to obtain both magnetic nanoparticles of pure materials (Co, Fe, Ni) and their alloys (FeNi, FeCo, etc.) and oxides, nitrides and carbides based on them [10,11]. The dispersion parameters of each batch of nanoparticles are related to the process parameters of EWE fusion, such as wire diameter, length of wire working section, capacitor battery charging voltage before each explosion, capacitor battery capacity, superheat factor (ratio of injected energy to sublimation energy of wire material), composition of gas mixture inside the blast chamber, etc. The gas system of the EWE unit contains separation devices to separate the produced nanoparticles into different size fractions [10,11]. Such a wide range of conditions for obtaining nanoparticles from the same material enables flexible adaptation of the functional properties of the powders by selecting the optimal 861