Programme

O.19 -- Oral, VCTP-50

Date: Tuesday, 5 August 2025

Time: 16:50 - 17:15

First-order magnetic transition and giant magnetic entropy change induced by random anisotropy in external fields

Phong H. Nguyen(1), Niem T. Nguyen (1), Huy D. Nguyen (1), Trung K. Giang (1), Hoai T.L. Nguyen (2), Cong T. Bach (1) and Giang H. Bach (1,*)

(1) Faculty of Physics, University of Science, Vietnam National University, 334 Nguyen Trai Street, Thanh Xuan, Hanoi, Vietnam. (2) Institute of Physics, Vietnam Academy of Science and Technology, 10 Dao Tan Street, Ba Dinh, Hanoi, Vietnam. * Corresponding e-mail: gbach@hus.edu.vn

This study explores first-order magnetic transitions (FOMT) and isothermal first-order magnetization processes (FOMP) in a two-dimensional (2D) spin system through Monte Carlo simulations applied to the spin-1 Blume-Capel model, incorporating random anisotropy under an external magnetic field. Significant variations in isothermal magnetic entropy are observed near the critical temperature $T_C^{(1)}$ of the FOMT when both the magnitude ($D$) and probability ($p$) of the random anisotropy are sufficiently high. The FOMT is characterized not only by an abrupt change in magnetization at $T_C^{(1)}$ but also by shifts in the distributions of energy and magnetization histograms. From these analyses, we construct a phase diagram illustrating the transition from a second-order magnetic transition (SOMT) to a FOMT, driven by random anisotropy, and compare it with previous findings in Ref. [1]. The calculated magnetic entropy change $|\Delta S_M|$ reveals a pronounced magnetocaloric effect near $T_C^{(1)}$, especially when the applied magnetic field approaches the critical threshold $h_{cr}$ associated with the FOMP. Additionally, the entropy change during the FOMT is notably greater than that observed in the SOMT under equivalent low-field conditions. Finally, the temperature-dependent magnetic properties near the FOMT are compared with experimental data from $\text{Cr}_{11} \text{Ge}_{19}$ samples. \\References: \\[1] E. C. Bezerra, M. Gomes da Silva, J. Ricardo de Sousa, Physica A 615 (2023) 128510.

Presenter: Nguyen Hai Phong