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Register a new userLarge magnetocaloric effect in Gd4Co3
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E. V. Sampathkumaran
Publication date
2008
fields
Physics
and research's language is
English
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We report a large entropy change (DeltaS) below 300 K, peaking near TC= 220 K, due to isothermal change of magnetic field, for Gd4Co3, with a refrigeration capacity higher than that of Gd. Notably, the isothermal magnetization is nonhysteretic - an important criterion for magnetic refrigeration without loss. DeltaS behavior is also compared with that of magnetoresistance.
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We present combined experimental and theoretical investigations on the magnetic and magnetocaloric behavior of Nd$_2$NiMnO$_6$. The relative cooling power (RCP) which quantifies the usefulness of a magnetocaloric (MC) material is estimated to be $approx 300$ J/Kg near the ferromagnetic transition at $T_C approx 195$ K. This RCP is comparable to the best known MC materials. Additionally, the magnetic entropy change has a broad profile ($T_C - 50~{rm K} < T < T_C + 50~{rm K}$) leading to an enhancement in the working-range of temperatures for magnetocaloric based cooling. These features make Nd$_2$NiMnO$_6$ a superior magnetocaloric material compared for example, to the nonmagnetic counterpart Y$_2$NiMnO$_6$. We identify the mechanism for the enhanced RCP which can guide search for future MC materials.
We investigate the magnetocaloric effect (MCE), relative cooling power (RCP) and crystalline structure in Sb substituted CrTe_{1-x}Sb_{x} (0 leq x leq 0.2) alloy. The Rietveld refinement of the XRD pattern of CrTe1-xSbx showed the emerging of pure hexagonal NiAs structure with P63/mmc (194) space group with increasing Sb substitution. We detect a slight increase in the basal plane a-lattice parameter, with a much larger reduction in the c-axis. Magnetic isotherms were measured in the temperature range of 50-400K. The results revealed an increase in the maximum entropy change |S_{M}(T,H)| with Sb-substitutions in the temperature range (~285-325K). Moreover, The RCP values increased by about 33% with 20% Sb substitutions. These findings suggest that CrTe_{1-x}Sb_{x} alloys can be used in room temperature magnetic cooling at fraction of the coast of pure Gd element the porotype magnetic material for magnetic refrigeration.
The magnetic and magnetocaloric (MCE) properties were studied in a stuffed honeycomb antiferromagnet GdInO3 polycrystalline. No long-range magnetic ordering was observed with only a sharp upturn in the temperature dependent magnetization curves at TN ~ 2.1 K. The large value of frustration index value ~ 5.0 suggests short-range antiferromagnetic interactions existing between the Gd3+ moments in this frustrated magnetic system. Negligible thermal and magnetic hysteresis suggest a second-order feature of phase transition and a reversible magnetocaloric effect (MCE) in GdInO3 compound. In the magnetic field changes of 0-50 kOe and 0-70 kOe, the maximum magnetic entropy change values are 9.31 J/kg K and 17.53 J/kg K near the liquid helium temperature, with the corresponding RCP values of 106.61 and 196.38 J/kg, respectively. The relative lower MCE performance of GdInO3 polycrystalline than the other Gd-based magnetocaloric effect is understood by the high magnetic frustration in this system. Our investigation results reveal GdInO3 polycrystalline has a large reversible MCE, which not only provides another possibility of exploiting magnetocaloric refrigerants in the frustrated magnetic systems near the cryogenic temperature region, but also serves to excavate more exotic properties in the frustrated stuffed honeycomb magnetic systems.
We report a novel negative magnetocaloric effect in CoMnSi_{1-x}Ge_{x} arising from a metamagnetic magnetoelastic transition. The effect is of relevance to magnetic refrigeration over a wide range of temperature, including room temperature. In addition we report a very high shift in the metamagnetic transition temperature with applied magnetic field. This is driven by competition between antiferromagnetic and ferromagnetic order which can be readily tuned by applied pressure and compositional changes.
The rotating magnetocaloric effect (RMCE) is a recent interest in magnetic refrigeration technique in which the cooling effect is attained by rotating the anisotropic magnetocaloric material from one orientation to the other in a fixed magnetic field. In this work, we report the anisotropic magnetocaloric properties of single crystals of the ferromagnetic Weyl semimetal Co$_{3}$Sn$_{2}$S$_{2}$ for magnetic field $Hparallel c$ axis and $Hparallel ab$ plane. We observed a significant (factor of $2$) difference between the magnetocaloric effect measured in both orientations. The rotating magnetocaloric effect has been extracted by taking the difference of the magnetic entropy change ($Delta S_{M}$) for fields applied in the two crystallographic orientations. In a scaling analysis of $Delta S_{M}$, the rescaled $Delta S_{M}(T,H)$ vs reduced temperature $theta$ curves collapse onto a single universal curve, indicating that the transition from paramagnetic to ferromagnetic phase at 174~K is a second order transition. Furthermore, using the power law dependence of $Delta S_{M}$ and relative cooling power RCP, the critical exponents $beta$ and $gamma$ are calculated, which are consistent with the recent critical behavior study on this compound cite{Yan2018}.
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