Magnetic entropy-change in La0.67−xBixCa0.33MnO3 compound

Bi doped lanthanum manganites with the chemical composition of La_0.67−xBi_xCa_0.33MnO₃ (x=0$x=0$, 0.05, 0.1, 0.2) were prepared by the standard solid-state process. The Curie temperatures were measured to be 267 K for x=0$x=0$, 248 K for x=0.05$x=0.05$, 244 K for x=0.1$x=0.1$ and 229 K for x=0.2$x=0.2$ samples. It was found that the maximum value of the magnetic entropy change ∣ΔS_m∣ has reached the highest value of 6.08 J/kg K at 3 T for the composition with x=0.05$x=0.05$. Nearly the same maximum entropy change was observed for the x=0$x=0$ sample. A large decrease in the magnitude of the entropy change was observed for the x=0.2$x=0.2$ sample.     

Magnetocaloric effect of Gd5SixSn4−x Alloys

The crystal structure and magnetocaloric effect of Gd₅Si_xSn_4−x   (with x=2.4$x=2.4$, 2.6 and 2.8) alloys were studied by means of X-ray power diffraction (XRD) and magnetic measurements. From the XRD results, these alloys adopt a Gd₅Si₄-type structure for x=2.8$x=2.8$, Gd₅Si₄-type and Gd₅Si₂Ge₂-type mixed structures for x=2.4$x=2.4$ and 2.6, while some minor phases can also be found. The Curie temperatures of the Gd₅Si_xSn_4−x increases gradually when x increases from 276 K for x=2.4$x=2.4$, to 301.5 K for x=2.8$x=2.8$. Magnetic entropy changes of these alloys at a magnetic field change of 0–1.8 T are 1.88, 2.26 and 1.69 J/kg K for x=2.4$x=2.4$, 2.6 and 2.8, respectively. The temperature-dependent XRD analysis shows that there is no crystallographic transition for these alloys, which can explain their low magnetic entropy changes.     

Effect of carbon content on structure and magnetic properties for (Fe,Ni)1−xCx by mechanical alloying

FCC (Fe₅₅Ni₄₅)_1−xC_x   supersaturated solid solution was prepared in a wide concentration range (0?x?0.9)$(0?x?0.9)$ by mechanical alloying of nanocrystalline Fe₅₅Ni₄₅ with graphite. The lattice constant of Fe₅₅Ni₄₅ increases linearly with increasing carbon content up to x=0.25$x=0.25$. At the same time, it is found that the magnetic moment per metal atom (Fe, Ni) decreases linearly with increasing carbon content for 0?x?0.25$0?x?0.25$ with a slope of 1.2 μ_B/at. For high carbon content, x?0.5$x?0.5$, it is observed that the decrease of lattice constant and increase of moment per metal atom (Fe, Ni) with increasing C content, indicates that the dissolution of carbon is hindered by the high-volume fraction of graphite in the initial powder mixture. The complete amorphization of x=0.5$x=0.5$ does not occur after the extended ball milling. The alloying effect of carbon on the magnetization is compared with other metalloid B, P, and Si in Fe- and Ni-based binary system.     

Effect of La doping on magnetotransport and magnetic properties of double perovskite Sr2FeMoO6 system

We have investigated the magnetotransport and magnetic properties on polycrystalline samples of Sr_2−xLa_xFeMoO₆ (x=0$x=0$, 0.2, 0.4, 0.6, 0.8 and 1.0). The magnitude of intergrain tunneling magnetoresistance with low magnetic field of 0.88 T for x=0.2$x=0.2$ and 0.4$0.4$ samples are as large as 5% and 7% at room temperature and 13% and 10% at 10 K, respectively. The increase of coercivity (_Hc$H_{\mathrm{c}}$), ratio of remanent magnetization with respect to saturation magnetization (_Mr/_Ms$M_{\mathrm{r}}/M_{\mathrm{s}}$), high saturation fields, and reduction of the saturation magnetization indicate that random disorder of spin orientation is mainly responsible for enhancement of the low-field magnetoresistance for samples with x?0.4$x?0.4$. Whereas rapid drop of _Hc$H_{\mathrm{c}}$, _Mr/_Ms$M_{\mathrm{r}}/M_{\mathrm{s}}$, _Mr$M_{\mathrm{r}}$, and saturation fields for samples with x>0.4$x>0.4$ signifies the growth of antiphase boundary, which gives rise to lower values of low-field MR.