Magnetic properties and magnetocaloric effects (MCEs) of ternary intermetallic ErFeSi compound have been investigated in detail. It is found that ErFeSi exhibits a second-order magnetic transition from ferromagnetic to paramagnetic states at the Curie temperature TC = 22 K, which is quite close to the liquid hydrogen temperature (20.3 K). A thermomagnetic irreversibility between zero-field-cooling and field-cooling curves is observed below TC in low magnetic field, and it is attributed to the narrow domain wall pinning effect. For a magnetic field change of 5 T, the maximum values of magnetic entropy change (−ΔSM) and adiabatic temperature change (ΔTad) are 23.1 J/kg K and 5.7 K, respectively. Particularly, the values of −ΔSM and refrigerant capacity reach as high as 14.2 J/kg K and 130 J/kg under a magnetic field change of 2 T, respectively. The large MCE without hysteresis loss for relatively low magnetic field change suggests that ErFeSi compound could be a promising material for magnetic refrigeration of hydrogen liquefaction.

Magnetic properties and magnetocaloric effects of Ho12Co7 compound are investigated by magnetization and heat capacity measurement. The Ho12Co7 compound undergoes antiferromagnetic (AFM)-AFM transition at T1 = 9 K, AFM-ferromagnetic (FM) transition at T2 = 17 K, and FM-paramagnetic transition at TC = 30 K, with temperature increasing. There are two peaks on the magnetic entropy change (ΔSM) versus temperature curves and the maximal value of –ΔSM is found to be 19.2 J/kg K with the refrigerant capacity value of 554.4 J/kg under a field change from 0 to 5 T. The shape of the ΔSM-T curves obtained from heat capacity measurement is in accordance with that from magnetization measurement. The excellent magnetocaloric performance indicates the applicability of Ho12Co7 as an appropriate candidate for magnetic refrigerant in low temperature ranges.

The magnetic properties and magnetocaloric effects (MCEs) of RGa (R = Tb and Dy) compounds are investigated. The TbGa compound exhibits two successive magnetic transitions: spin-reorientation (SR) transition at TSR = 31 K and second-order ferromagnetic (FM)–paramagnetic (PM) transition at Curie temperature TC = 154 K, while the DyGa compound undergoes a SR transition with TSR=25 K and a FM–PM transition with TC = 113 K. It is noteworthy that a broad distribution of the magnetic entropy change peak is observed. The values of the refrigerant capacity (RC) for TbGa and DyGa are found to be 620.6 and 381.9 J/kg for a field change of 0–5 T, respectively. And for a field change of 0–7 T, the values are 900 and 584.2 J/kg, respectively. The large value of RC for TbGa and DyGa originates from the combined contribution from SR and FM–PM transitions, which enlarges the temperature span of large MCE.

Effect of magnetic polarons on the magnetic, magnetocaloric, and magnetoresistance properties of the intermetallic compound HoNiAl Large magnetic entropy change in the metallic antiperovskite Mn 3 GaCThe magnetic properties and magnetocaloric effect (MCE) of PrGa compound are studied in detail. Both thermomagnetization curves and heat capacity curves indicate that PrGa compound undergoes a transition from ferromagnetic (FM) to antiferromagnetic (AFM) phase at T t $ 27 K and a transition from AFM to paramagnetic (PM) phase at T 0 $ 37 K with increasing temperature. As the applied field increases, the magnetic state between T t and T 0 shows an obvious metamagnetic transition from AFM to FM state. The magnetic entropy change (DS M ) calculated from magnetic property measurement and that obtained from heat capacity measurement are in good agreement with each other above 25 K. Instead of peak like distribution, nearly constant value of DS M in a temperature range from 29.5 K to 37.5 K is observed when the field change is 0-5 T. The adiabatic temperature change (DT) also shows similar change rules. This characteristic of MCE is very important for the practical applications of magnetic refrigerant materials. V C 2014 AIP Publishing LLC. [http://dx.

The effects of the interstitial C and H atoms on the phase formation, the hysteresis loss, and magnetocaloric effects of the NaZn13-type La(Fe, Si)13 compounds are investigated. It is found that the annealing time to obtain a 1:13 structure is significantly reduced from 40 days for LaFe11.7Si1.3 to a week for LaFe11.7Si1.3C0.2. The introduction of C and H atoms can adjust Curie temperature to around room temperature and leads to the decrease in magnetic entropy change (ΔSM) and magnetic hysteresis loss due to the weakening of itinerant-electron metamagnetic transition. Large −ΔSM of 19.0 J/kg K at room temperature without hysteresis loss for LaFe11.7Si1.3C0.2H1.7 is obtained for a field change of 5 T.

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Magnetoelectric multiferroic fluids composed of BaTiO3@CoFe2O4 composite nanoparticles dispersed in a highly insulating nonpolar oleic acid/silicone oil mixture have been developed. The effects of the particle volume fraction and a magnetic field, as well as an electric field, on the ferroelectric and magnetic properties, as well as the magnetoelectric coupling effect, have been systematically studied and discussed in this paper. Magnetic characterization shows an approximation to superparamagnetism, and both the remanent magnetization (Mr) and the coercive field (Hc) increase with increases in the volume fraction and applied electric field. Similarly, a superparaelectric state has been observed in the multiferroic fluids, in which both the remanent polarization (Pr) and the coercive field (Ec) are near zero, whereas they increase with increases in the applied magnetic field and volume fraction. High converse and direct magnetoelectric coupling coefficients are estimated to be αH = 8.16 × 10-4 (Oe cm) V-1 and αE = 1.58 × 104 V (cm Oe)-1, respectively. Further analysis indicates that the composite particles can be aligned under an external magnetic/electric field so that their magnetic/electric moments can be parallel to the external field, which in turn results in changes in the magnetization/polarization directions. These results imply that besides magnetoelectric fluids that consist of core/shell-structured nanoparticles, conventional multiferroic fluids based on composite particles may provide an opportunity to gain electrical control of magnetization and vice versa, which implies potential applications.

Multiferroics are of interest for applications as the magnetoelectric coupling effect between ferroelectric and magnetic order parameters. Here, an approach to control and switch the ferromagnetic orientation with an electric field using the multiferroic fluids is reported. A new multiferroic material, the so‐called magnetoelectric multiferroic fluids, has been prepared by distributing surface treated Ni0.5Zn0.5Fe2O4@CoFe2O4 core–shell structured particles in to a highly insulating silicone oil. An electromagnetic coupling phenomenon is used that is manifested in core–shell structure consisting of a ferromagnetic Ni0.5Zn0.5Fe2O4 wrapped tightly with the ferroelectric BaTiO3 in the fluid, which is based on magnetoelectric coupling at the interface between a ferromagnet and the ferroelectric. Three general manifestations of the coupling interactions are discovered, the first is that the hysteresis loops tend to shift from the origin along the voltage axis toward the positive or positive direction, an exchange bias like behavior, a consequence of pinned effect; the second is an enhancement of the coercive field of the ferromagnet as a consequence of enhanced rotate drag effect; and the third one is the improved residual magnetization. The results imply that conventional core–shell structured multiferroic fluids may have an opportunity to gain electrical control of the magnetization.