Presentation Information
[P1-74]Magnetocaloric effect of textured polycrystalline RNi5 alloys
*Iurii Koshkidko1, Jacek Ćwik1 (1. Institute of Low Temperature and Structure Research, PAS, Okólna 2, Wrocław, 50-422 (Poland))
Keywords:
Magnetocaloric effect,Magnetic phase transition,Magnetocrystalline anisotropy,Intermetallic compounds,Rare earth metals
The study of the magnetocaloric effect (MCE) is relevant for application in energy-saving magnetic refrigeration technology (MRT). The application of MRT in the low-temperature region can contribute to increasing the efficiency of manufacturing and application of liquid gases (e.g. helium, hydrogen, nitrogen, natural gases, etc.), and will also reduce losses associated with their transportation and storage. It is known that the physics of magnetic phenomena consider two main types of MCE. The first one is the MCE of paraprocess, i.e., MCE related to the process of ordering magnetic moments during magnetization of a magnetic material in a magnetic field, which were disordered as a result of thermal fluctuations [1]. The second type is the rotating (anisotropic) MCE (RMCE) caused by the magnetization rotation as a result of the magnetization of the magnetic materials along the hard magnetization axis of the magnetic materials. The MCE of paraprocess is fairly well studied, while the RMCE remains rather poorly understood. First of all, this is related to difficulties in creating samples and methods for such investigations. In [2], it was theoretically shown that the RMCE values for RNi5 compound can reach the giant value ΔTad = 5.5 K in a field of 1 T at a temperature of 7 K for ErNi5. For comparison, the previously experimentally observed giant rotating MCE in the region of spin-reorientation transition in NdCo5 single crystal was ΔTad = 1.6 K in a field of 1.3 T at a temperature of 278 K [3].
The authors of works [2] highlight that experimental data on the anisotropic MCE for RNi5 are still absent.Intermetallic compounds RNi5 are excellent model objects for studying the mechanisms of formation of magnetic properties in 4f and 3d-metal compounds. They have a hexagonal structure of the CaCu5 type. The 3d-band of Ni is practically occupied by the external electrons of R atoms. As a consequence, the Ni atoms do not contribute significantly to the spontaneous magnetic moments of RNi5. Therefore, RNi5 with non-magnetic R=La, Ce, Lu or Y are Pauli paramagnetics . RNi5 compounds with magnetic R = Nd, Sm, Gd, Tb, Dy, Ho and Er are ferromagnets with Curie TC temperatures lying below 32 K. In turn, strong magnetocrystalline anisotropy (MCA) is observed in RNi5 compounds with magnetic R. For R=Sm, Er, Tm, the “ easy axis” type of MCA is characteristic, and for R=Pr, Nd, Tb, Dy, Ho “ easy plane” [4].Recently, polycrystalline magnetocaloric materials with RMCE have attracted more attention due to their more convenient sample preparation than monocrystalline materials [5]. The induced magnetic anisotropy in such materials is realised by texturing magnetic powder in a strong magnon field followed by fixation in a non-magnetic matrix or by directed crystallisation. The latter method was used in this work to create polycrystalline samples of RNi5 with induced magnetic anisotropy.Polycrystalline alloy RNi5 was synthesised by arc melting of the elements in a purified argon atmosphere in a water-cooled copper crucible. The arc-melted ingot was inverted and remelted four times to ensure homogeneity. Microstructures were observed using a scanning electron microscope and grain orientation was investigated using electron backscattered electron diffraction (EBSD).To investigate MCE in medium magnetic fields (up to 1.8 T), we used a magnetic field source based on permanent magnets (produced by AMT&C) and an apparatus for direct MCE measurements placed on a rotary table [6]. This allowed measurements in different directions relative to the main axis of the magnetic texture of the sample. This method is of particular interest because the magnitude of the magnetic field corresponds to that to be used in magnetic refrigeration systems.In this work we present the results of the MCE study by direct method of synthesised polycrystalline RNi5 with induced magnetic anisotropy (See Fig.). The influence of magnetocrystalline anisotropy on the magnitude of RMCE is discussed.The work was supported by the National Science Center, Poland through the OPUS Program under Grant No. 2024/53/B/ST11/02445. [1] Tishin A.M., Spichkin Y.I., “The magnetocaloric effect and its applications”, Institute of Physics Publishing, Bristol, Philadelphia, 2003, 475 p.[2] N.A. de Oliveira, Journal of Physics and Chemistry of Solids 103 (2017) 13–15[3] Nikitin, S., Skokov, K., Koshkid'ko, Yu., Pastushenkov, Yu., Ivanova, T., PRL 105 (2010) 137205[4] W.E. Wallace, Rare-Earth Intermetallics, Academic Press, New York, London (1973) p. 266.
[5] Xiaoyu Zhou, et al., Appl. Phys. Lett. 120, 132401 (2022)
[6] Koshkid'ko, Y.S., Ćwik, J., Ivanova, T.I., Nikitin, S.A., Miller, M., Rogacki, K., JMMM 433 (2017) 234
The authors of works [2] highlight that experimental data on the anisotropic MCE for RNi5 are still absent.Intermetallic compounds RNi5 are excellent model objects for studying the mechanisms of formation of magnetic properties in 4f and 3d-metal compounds. They have a hexagonal structure of the CaCu5 type. The 3d-band of Ni is practically occupied by the external electrons of R atoms. As a consequence, the Ni atoms do not contribute significantly to the spontaneous magnetic moments of RNi5. Therefore, RNi5 with non-magnetic R=La, Ce, Lu or Y are Pauli paramagnetics . RNi5 compounds with magnetic R = Nd, Sm, Gd, Tb, Dy, Ho and Er are ferromagnets with Curie TC temperatures lying below 32 K. In turn, strong magnetocrystalline anisotropy (MCA) is observed in RNi5 compounds with magnetic R. For R=Sm, Er, Tm, the “ easy axis” type of MCA is characteristic, and for R=Pr, Nd, Tb, Dy, Ho “ easy plane” [4].Recently, polycrystalline magnetocaloric materials with RMCE have attracted more attention due to their more convenient sample preparation than monocrystalline materials [5]. The induced magnetic anisotropy in such materials is realised by texturing magnetic powder in a strong magnon field followed by fixation in a non-magnetic matrix or by directed crystallisation. The latter method was used in this work to create polycrystalline samples of RNi5 with induced magnetic anisotropy.Polycrystalline alloy RNi5 was synthesised by arc melting of the elements in a purified argon atmosphere in a water-cooled copper crucible. The arc-melted ingot was inverted and remelted four times to ensure homogeneity. Microstructures were observed using a scanning electron microscope and grain orientation was investigated using electron backscattered electron diffraction (EBSD).To investigate MCE in medium magnetic fields (up to 1.8 T), we used a magnetic field source based on permanent magnets (produced by AMT&C) and an apparatus for direct MCE measurements placed on a rotary table [6]. This allowed measurements in different directions relative to the main axis of the magnetic texture of the sample. This method is of particular interest because the magnitude of the magnetic field corresponds to that to be used in magnetic refrigeration systems.In this work we present the results of the MCE study by direct method of synthesised polycrystalline RNi5 with induced magnetic anisotropy (See Fig.). The influence of magnetocrystalline anisotropy on the magnitude of RMCE is discussed.The work was supported by the National Science Center, Poland through the OPUS Program under Grant No. 2024/53/B/ST11/02445. [1] Tishin A.M., Spichkin Y.I., “The magnetocaloric effect and its applications”, Institute of Physics Publishing, Bristol, Philadelphia, 2003, 475 p.[2] N.A. de Oliveira, Journal of Physics and Chemistry of Solids 103 (2017) 13–15[3] Nikitin, S., Skokov, K., Koshkid'ko, Yu., Pastushenkov, Yu., Ivanova, T., PRL 105 (2010) 137205[4] W.E. Wallace, Rare-Earth Intermetallics, Academic Press, New York, London (1973) p. 266.
[5] Xiaoyu Zhou, et al., Appl. Phys. Lett. 120, 132401 (2022)
[6] Koshkid'ko, Y.S., Ćwik, J., Ivanova, T.I., Nikitin, S.A., Miller, M., Rogacki, K., JMMM 433 (2017) 234
