SKM 2023 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 19: Focus Session: New Perspectives for Adiabatic Demagnetization Refrigeration in the Kelvin and sub-Kelvin Range (joint session TT/MA)

TT 19.9: Vortrag

Dienstag, 28. März 2023, 13:00–13:15, HSZ 03

Study of the large rotational magnetocaloric effect in Ni(en)(H₂O)₄SO₄·2H₂O — •Róbert Tarasenko, Petro Danylchenko, Erik Čižmár, Vladimír Tkáč, Alexander Feher, Alžbeta Orendáčová, and Martin Orendáč — Institute of Physics, Faculty of Science, Pavol Jozef Šafárik University, Park Angelinum 9, 041 54 Košice, Slovakia

The title compound Ni(en)(H₂O)₄SO₄·2H₂O (en = ethylenediamine) has been identified as a spin-1 paramagnet with the nonmagnetic ground state introduced by the easy-plane anisotropy D/k_B = 11.6 K with E/D = 0.1 and negligible exchange interactions J≈ 0. We present an experimental study of the rotational magnetocaloric effect (MCE) in single crystals at temperatures above 2 K, associated with adiabatic crystal rotation between the easy plane and hard axis in magnetic fields up to 7 T. The experimental observations are completed with ab initio calculations of the anisotropy parameters. Theoretical simulations of the rotational MCE in the S = 1 paramagnet were performed and the simulations were compared with experimental data. A large rotational magnetic entropy change ≈16.9 Jkg⁻¹K⁻¹ has been achieved in 7 T. The adiabatic rotation of the crystal in 7 T starting at the initial temperature of 4.2 K leads to the cooling of the sample down to 0.34 K, which suggests the application of this material in low-temperatures cooling. Our simulations show that S = 1 Ni(II)-based systems with easy-plane anisotropy can have better rotational magnetocaloric properties than costly materials containing rare-earth elements.

Supported by project No. APVV-18-0197.