Manipulation of magnetic transition and improvement of magnetocaloric effect in Ti–substituted Ho2CoMnO6 double perovskite

The magnetic refrigeration is achieved through the magnetocaloric effect of a magnetic system, which is considered a promising technology for achieving the required low temperatures in industry, daily life, and scientific research. This work experimentally investigates the magnetic behavior and magnetocaloric performance of Ho 2 CoMn 1- x Ti x O 6 (0 ≤ x  ≤ 1) double perovskites. The experimental results reveal that a paramagnetic →ferromagnetic transition characterized by a sharp increase in magnetization is suppressed due to decoupling action of Ti 4+ with 3 d 0 spin configuration. As a result, the transition temperature T C reduces monotonically from 75 K at x  = 0–37 K at x  = 0.6, and no obvious ferromagnetic transition is identified at x  = 0.8–1 due to the lack of Co 2+ –Mn 4+ interactions at so high Ti 4+ substitution concentration. In addition, the magnetocaloric effect is investigated by measuring the isothermal initial magnetization from 4 K to a temperature far above T C . The maximum magnetic entropy ( − Δ S M max ) under Δ H  = 6 T does not exhibit significant variation from x  = 0 (11.1 J kg −1  K −1 ) to 0.6 (11.5 J kg −1  K −1 ), while it increases noticeably from x  = 0.8 (13.9 J kg −1  K −1 ) to 1 (17.2 J kg −1  K −1 ). The present work indicates that the cryogenic magnetocaloric effect can be improved by dilution effect of nonmagnetic ions.