A technology of obtaining the single-phase ceramic samples of La1-xKxMnO3 manganites and the dependence of their structural parameters on the content of potassium has been described. Magnetocaloric effect (MCE) in the obtained samples has been measured by two independent methods: by classical direct methodic and by a method of magnetic field modulation. The values of MCE obtained by both methods have been substantially differed. The explanation of the observed divergences is given. The correlation between the level of doping and MCE value has been defined. The value of TC determined by the MCE maximum has been conformed to the literature data received by other methods.
Despite extensive researches on manganites owing to widespread use in modern electronics, this class of metal oxides does not cease to surprise with its unique properties and new phenomena. Here we have studied structural and magnetic properties of non-Heisenberg manganite nanoparticles with a strong spin-electron coupling. During transition from low temperature ferromagnetic to high temperature paramagnetic state, the change in charge, valence and spin (magnetic moment) with the localization of eg-electrons on the manganese ions have been detected. With decrease in a temperature, the overstat…
Processing magnetocaloric materials into magnetic refrigerants with appropriate shapes is essential for the development of magnetic refrigeration systems. In this context, the impact of processing on the physical properties of magnetocaloric materials is one of the important issues. Here, we investigate the crystallographic, magnetic, and magnetocaloric properties of gas-atomized particles of the intermetallic compound ErCo$_{2}$, a giant magnetocaloric material for low-temperature applications. The results demonstrate that the physical properties of ErCo$_{2}$ are significantly changed by ato…
We investigate the magnetic, thermal, and magnetocaloric properties of the intermetallic HoAl$_{3}$ compounds with two different crystal structures. The room-temperature equilibrium trigonal phase HoAl$_{3}$ undergoes an antiferromagnetic (AFM) transition at the Neel temperature $T^{\rm tri}_{\rm N} =$ 9.8 K. The AFM ordering of the compound is strong against the magnetic field, so that inverse magnetocaloric effect (MCE) is found even under a magnetic field change of 0-50 kOe. The high-pressure cubic phase HoAl3, prepared by a rapid-solidification process, is antiferromagnetically ordered bel…
As materials with suppressed ordering temperatures and enhanced ground state entropies, frustrated magnetic oxides are ideal candidates for cryogenic magnetocaloric refrigeration. While previous materials design has focused on tuning the magnetic moments, their interactions, and density of moments on the lattice, there has been relatively little attention to frustrated lattices. Prior theoretical work has shown that the magnetocaloric cooling rate at the saturation field is proportional to a macroscopic number of soft mode excitations that arise due to the classical ground state degeneracy. Th…
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 mag…
We report complex magnetic, magnetoresistance (MR) and magnetocaloric properties of Gd4RhAl and Tb4RhAl forming in the Gd4RhIn type cubic structure. Though the synthesis of the compounds was reported long ago, to our knowledge, no attempt was made to investigate the properties of these compounds. The present results of ac and dc magnetization, electrical resistivity and heat-capacity measurements down to 1.8 K establish that these compounds undergo antiferromagnetic order initially, followed by complex spin-glass features with decreasing temperature. These characteristic temperatures are: For …
We report the characteristic magnetic properties of several members of the rare-earth garnet family, Gd$_3$Ga$_5$O$_{12}$ (GGG), Dy$_3$Ga$_5$O$_{12}$ (DGG), Tb$_3$Ga$_5$O$_{12}$ (TGG), and Nd$_3$Ga$_5$O$_{12}$ (NGG), and compare their relative potential utility for magnetocaloric cooling, including their minimal adiabatic demagnetization refrigeration (ADR) temperatures and relative cooling parameters. A main objective of this work concerns the identification of potential improvements over the magnetocaloric properties of GGG for use in low temperature ADR cryostats. Using Tb$^{+3}$ and Dy$^{+…
Magnetic and magnetocaloric properties of quasi-one-dimensional Ising spin chain CoV$_{2}$O$_{6}$
通过磁化强度和热容测量研究了反铁磁Ising自旋链CoV $_{2}$ O $_{6}$的磁性和磁热性质.单斜晶系的$α$ $_{2}$ O $_{6}$和三斜晶系的$γ$ $_{2}$ O $_{6}$都表现出通过具有1/3磁化平台的中间亚铁磁态从反铁磁态到铁磁态的场诱导变磁转变.由于这种场致变磁转变，这些系统显示出大的常规以及逆磁热效应。在$α$ $_{2}$ O $_{6}$中，当沿$c$轴施加磁场时，我们观察到低温下场诱导的复杂磁相和多个磁化平台。从磁化强度、磁熵变和热容的温度和场依赖性确定了几个临界温度和场，构建了$H$ - $T$相图。与$α$ $_{2}$ O $_{6}$相比，$γ$ $_{2}$ O $_{6}$显示出相对简单的磁相图.由于在低或中等外加磁场下具有大的磁熵变和绝热温度变化，$γ$ -CoV $_{2}$ O $_{6}$可以被认为是低温区的磁制冷剂。
The magnetic properties and magnetocaloric effect of an intermetallic compound $\mathrm{Er_2Rh_3Si}$ was investigated by performing temperature dependence of dc- and ac-magnetic susceptibility and isothermal magnetizations. Polycrystalline $\mathrm{Er_2Rh_3Si}$ compound with $\mathrm{Mg_2Ni_3Si}$-type of rhombohedral Laves phases (space group $R\overline{3}m$, hR18) structure was synthesized by arc-melting method. The ac- and dc-magnetic susceptibility results revealed that the compound exhibited ferromagnetic order with $T_C$ $\approx$ 18 K. The obtained isothermal magnetic entropy changes ($…
3d-4f spin interaction induced giant magnetocaloric effect in zircon-type DyCrO4 and HoCrO4 compounds
通过磁化强度和热容测量研究了3d-4f自旋相互作用对DyCrO $_4$和HoCrO $_4$化合物磁性和磁热性质的影响。由于铁磁和反铁磁超交换相互作用的强烈竞争，这两种化合物在铁磁转变前后都表现出复杂的磁性和巨大的磁熵变。当磁场变化为8 T时，磁熵变的最大值（$ΔS_{M}^{max}$），绝热温度变化（$ΔT_{ad}$）和制冷剂容量（RC）对于DyCrO $_4$分别达到29 J kg $^{-1}$ K $^{-1}$、8 K和583 J kg $^{-1}$，而对于HoCrO $_4$的相应值分别为31 J kg $^{-1}$ K $^{-1}$、12 K，和622 J kg $^{-1}$。对于中等场变化，$ΔS_{M}^{max}$、$ΔT_{ad}$和RC也相当大。锆型DyCrO $_4$和HoCrO $_4$具有较大的磁热参数，是一种具有潜力的氢液化磁制冷材料。
We investigate the effect of partial replacement of extended 5d Ir4+ sites by localized 3d Cr3+ moments on the magnetocaloric properties of Y2Ir2O7 (YIO) pyrochlore iridates. We find that Y2Ir2-xCrxO7 (YICO) undergoes cluster glass transition, possibly due to RKKY like interaction between localized Cr3+ moments occupying random sites in the pyrochlore network, mediated by 5d Ir conduction electrons. The coexistence of ferromagnetic and antiferromagnetic clusters give rise to the conventional and inverse magnetocaloric effect (MCE). We observe significant enhancement of conventional as well as …
The paper contains the discussion of the magnetocaloric and electrocaloric effect in a model dimer (pair cluster). The system of interest is modelled with a Hubbard Hamiltonian including the external electric and magnetic field. The thermodynamics of such pair is described exactly, on the grounds of the grand canonical ensemble, focusing on the half-filling of energy states. The quantities of interest, such as magnetic entropy, magnetic specific heat as well as isothermal entropy change resulting from the variation of either electric or magnetic field and appropriate Grüneisen ratios are calcu…
Spherical nanoparticles (NPs) of size 14 nm, made of intermetallic Fe2CoAl (FCA) Heusler alloy, are synthesized via the co-precipitation and thermal deoxidization method. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns confirm that the present nanoalloy is crystallized in A2-disordered cubic Heusler structure. Magnetic field (H) and temperature (T) dependent magnetization (M) results reveal that the NPs are soft ferromagnetic (FM) with high saturation magnetization (Ms) and Curie temperature (Tc). Fe2CoAl nanoalloy does not follow the Slater Pauling (SP) rule, po…
