RESUMO
Giant magnetocaloric materials are highly promising for technological applications in magnetic refrigeration. Although giant magnetocaloric effects were discovered in first-order magnetic transition materials, it is accompanied by some non-desirable drawbacks, such as important hysteretic phenomena, irreversibility of the effect, or poor mechanical stability, which limits their use in applications. Here, we report the discovery of a giant magnetocaloric effect in commercialized Ho2O3 oxide at low temperature (around 2 K) without hysteresis losses. Ho2O3 is found to exhibit a second-order antiferromagnetic transition with a Néel temperature of 2 K. At an applied magnetic field change of 5 T and below 3.5 K, the maximum value of magnetic entropy change [Formula: see text], the refrigerant capacity (RC) were found to be 31.9 J.K-1.kg-1 and 180 J.K-1, respectively.
RESUMO
The influence of Zn substitution on the magnetic and magnetocaloric properties of Cd1-xZnxCr2Se4 (0.35 ≤ x ≤ 0.45) spinel was investigated. All the samples exhibited two successive magnetic transitions associated with the reentrant spin glass at a freezing temperature (Tf) and Curie temperature (TC). It was demonstrated that Tf changed slightly with the Zn content; however, the TC value decreased with increasing Zn content due to the decrease of lattice constant. The magnetic entropy variation (-ΔSM) was found to exhibit two maxima at TC and Tf, which have an opposite trend as a function of Zn content. With increasing Zn content, (-ΔSM) was found to decrease at TC, whereas at Tf, (-ΔSM) increased. It was shown that the change of (-ΔSM) is closely correlated to the local exponent factor n at both transitions. The results showed that materials with double magnetic transitions could be integrated in a new class of magnetic refrigeration working in different temperature windows.
RESUMO
Low-dimensional magnetic heterostructures are a key element of spintronics, where magnetic interactions between different materials often define the functionality of devices. Although some interlayer exchange coupling mechanisms are by now well established, the possibility of direct exchange coupling via proximity-induced magnetization through non-magnetic layers is typically ignored due to the presumed short range of such proximity effects. Here we show that magnetic order can be induced throughout a 40-nm-thick amorphous paramagnetic layer through proximity to ferromagnets, mediating both exchange-spring magnet behaviour and exchange bias. Furthermore, Monte Carlo simulations show that nearest-neighbour magnetic interactions fall short in describing the observed effects and long-range magnetic interactions are needed to capture the extent of the induced magnetization. The results highlight the importance of considering the range of interactions in low-dimensional heterostructures and how magnetic proximity effects can be used to obtain new functionality.
