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We report magnetic properties and magnetocaloric (MC) effect in Fe90-xNixZr10 (x = 0, 5, 10, and 15) alloy ribbons prepared by rapid-quenching method. We found the Curie temperature (TC) of the alloy ribbons depends strongly on Ni-doping concentration (x) increasing from 245 K for (x = 0), through 306 K (for x = 5) up to TC = 403 (for x = 15). Also, the dependence of the maximum magnetic entropy change (|ΔSmax|) on Ni content was readily apparent. Indeed, for the x = 0 and 5 samples that have TC around room temperature, the |ΔSmax| values increment under magnetic field changes of 10, 20, and 40 kOe was found to be as high as 0.87, 1.76, and 3.04 J·kg-1·K-1 for x = 0, and 1.03, 1.90, and 3.26 J·kg-1·K-1 for x = 5, respectively. These values correspond to refrigerant capacity in the range of 86-334 J·kg-1 and are comparable to other known MC materials. High magnetocaloric performance in rare-earth-free non-expensive metallic alloys indicates that these materials could be competitive candidate for active magnetic refrigeration at room temperature. [ABSTRACT FROM AUTHOR]

We have studied the magnetic properties and magnetocaloric effect of LaFe10-xBxSi3 (x = 1, 2, and 3) alloy ribbons prepared by a rapidly quenching method. The partial replacement of Fe for B in LaFe10-xBxSi3 leads to a rapid decrease in the Curie temperature (TC) from 425 K for x = 1, through 310 K for x = 2, to 190 K for x = 3. Among LaFe10-xBxSi3 ribbons, only LaFe7B3Si3 (i.e., x = 3) has a dominancy of amorphous phase. The M2 versus H/M plots prove this sample exhibiting a second-order magnetic phase transition. The detailed analyses of M(H) data around TC based on the modified Arrott plot introduced critical values of TC ≈ 192 K, β = 0.354 ± 0.013, γ = 1.355 ± 0.032, and δ = 4.8 ± 0.1. These values are close to those expected for the 3D-Heisenberg model (β = 0.365 and γ = 1.336), indicating an existence of ferromagnetic short-range interactions. Concerning the magnetic entropy change (ΔSm), we have found its maximum ΔSm achieved just around TC, which are 1.04 and 1.42 J/kg K for x = 2 and 3, respectively, under an applied field of 50 kOe. This result proves the ΔSm increase with increasing B content in LaFe10-xBxSi3 alloy ribbons. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the magnetic properties and the magnetocaloric effect of La 0.7−x Na x Ca 0.3 MnO 3 compounds, which were prepared by a conventional solid-state reaction technique. The Rietveld refinement results suggested that the samples are single phase belonging to an orthorhombic structure (space group Pnma ). Analyzing temperature dependence of magnetization M ( T ) revealed that the Curie temperature ( T C ) increases with increasing Na content ( x ). Their T C value is found to be 260–298 K for x =0.0–0.1, respectively. Base on M ( T ) data measured at different applied magnetic fields ( H ), temperature dependence of magnetic entropy change Δ S m ( T ) data for all the samples was calculated by using a phenomenological model. In the vicinity of T C, -Δ S m ( T ) curve reaches a maximum value (denoted as |Δ S max |), which gradually increases with increasing H . Under 12 kOe, the value of |Δ S max | is in a range of 1.47–5.19 J/kg K corresponding to the relative cooling power RCP=57.12–75.88 J/kg. Applied the universal master curve method for the magnetic entropy change, we concluded that Na-doped in La 0.7−x Na x Ca 0.3 MnO 3 compounds leads to modification the nature of the magnetic phase transition from the first- to the second-order. [ABSTRACT FROM AUTHOR]