A strong electronic reconstruction resulting in a quenching of the Fe magnetic moments has recently been predicted to be at the origin of the giant magnetocaloric effect displayed by Fe2Pbased materials. To verify this scenario, X-ray Magnetic Circular Dichroism experiments have been carried out at the L edges of Mn and Fe for two typical compositions of the (Mn,Fe)2(P,Si,B) system. The dichroic absorption spectra of Mn and Fe have been measured element specific in the vicinity of the first-order ferromagnetic transition. The experimental spectra are compared with first-principle calculations and charge-transfer multiplet simulations in order to derive the magnetic moments. Even though signatures of a metamagnetic behaviour are observed either as a function of the temperature or the magnetic field, the similarity of the Mn and Fe moment evolution suggests that the quenching of the Fe moment is weaker than previously predicted.
Role of Fe substitution on the anomalous magnetocaloric and magnetoresistance behavior in Tb(Ni1-xFex)2 compounds
我们报告的磁性，磁热和磁电阻的结果在Tb（Ni 1-xFex）2化合物与x=0，0.025和0.05。Fe取代导致的有序温度从36 K x=0到124 K x=0.05的增加。与TbNi 2中看到的单个尖锐MCE峰相反，Fe取代的化合物的MCE峰相当宽。我们把这种反常的MCE行为归因于Fe取代引起的Tb矩的随机化。磁性和磁阻的结果似乎证实了这一命题。本研究还表明，在本化合物中观察到的异常磁热和磁电阻行为类似于Ho（Ni，Fe）2化合物。
Using Density Functional Theory and a thermodynamic model [Physical Review B 86, 134418 (2012)], in this paper, we provide an approach to systematically screen compounds of a given Heusler family to predict ones that can yield giant magnetocaloric effect driven by a first-order magneto-structural transition. We apply this approach to two Heusler series Ni$_{2-x}$Fe$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$ and Ni$_{2-x}$Co$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$, obtained by cosubstitution at Ni and Mn sites. We predict four new compounds with potentials to achieve the target properties. Our computation…
Processing magnetocaloric materials into magnetic refrigerant particles is an essential issue in developing high-performance magnetic refrigerators. Here, we succeed in stably producing magnetocaloric particles of the promising material HoAl2 by a newly devised method based on electrode induction melting gas atomization process. The particle size range is on the order of submillimeter, which is suitable for practical refrigeration systems. The resulting particles with less contamination have good morphological, magnetic, and magnetocaloric properties: (i) almost spherical shapes with few inter…
The crystal and magnetic structures of AlFe2B2 have been studied with a combination of X-ray and neutron diffraction and electronic structure calculations. The magnetic and magnetocaloric properties have been investigated by magnetisation measurements. The samples have been produced using high temperature synthesis and subsequent heat treatments. The compound crystallises in the orthorhombic crystal system Cmmm and it orders ferromagnetically at 285 K through a second order phase transition. At temperatures below the magnetic transition the magnetic moments align along the crystallographic $a$…
The first order magneto-structural transition ($T_t\simeq95$ K) and magnetocaloric effect in MnNiGe$_{0.9}$Ga$_{0.1}$ are studied via powder x-ray diffraction and magnetization measurements. Temperature dependent x-ray diffraction measurements reveal that the magneto-structural transition remains incomplete down to 23 K, resulting in a coexistence of antiferromagnetic and ferromagnetic phases at low temperatures. The fraction of the high temperature Ni$_2$In-type hexagonal ferromagnetic and low temperature TiNiSi-type orthorhombic antiferromagnetic phases is estimated to be $\sim 40\%$ and $\s…
Large thermal hysteresis in the MnFe(P, Si, B) system hinders the heat exchange rate and thus limits the magnetocaloric applications at high frequencies. Substitution of Mn by V in Mn1-xVxFe0.95P0.593Si0.33B0.077 and Mn1-xVxFe0.95P0.563Si0.36B0.077 alloys was found to reduce the thermal hysteresis due to a decrease in the latent heat. Introducing V increases both the field-induced transition temperature shift and the magnetic moment per formula unit. Thus, a decease in the thermal hysteresis is obtained without losing the giant magnetocaloric effect. In consequence, an ultralow hysteresis (0.7…
We report a systematic investigation of the magnetic and magnetocaloric properties of Dy5Pd2 and Dy5PdNi. Our study on these compounds gave evidence that they exhibit complex magnetic behaviour along with the presence of glass-like magnetic phase. Furthermore, in these compounds both second order and first order phase transitions were present, which were validated through Arrott plots and Landau parameter analysis. AC susceptibility along with time dependent magnetisation study has confirmed the presence of double cluster glass-like freezing in both Dy5Pd2 and Dy5PdNi. These compounds show sig…
We report the structural, magnetic properties, and magnetocaloric effect of a new polycrystalline compound of $\mathrm{Tb_2Rh_3Ge}$. This present compound crystallizes with $\mathrm{Mg_2Ni_3Si}$-type of rhombohedral Laves phases (space group $R\overline{3}m$, hR18). The magnetic properties and magnetocaloric effect of the $\mathrm{Tb_2Rh_3Ge}$ is explored through dc-magnetization measurements. Temperature dependence of magnetization revealed that the compound exhibits ferromagnetic behavior with $T_C$$=$56 K. The field dependence of magnetization indicates that $\mathrm{Tb_2Rh_3Ge}$ is a soft …
We have employed Gd55Co30NixAl15-x (x = 10, 5 and 0) amorphous microwires as a model system to unravel the impact of multiple magnetic interactions on the magnetism and the magnetocaloric behavior in Gd-alloy microwire systems. Our study shows that in addition to the RKKY ferromagnetic (FM) interaction (Gd-Gd), antiferromagnetic (AFM) interactions (Gd-Co, Gd-Ni) coexist and contribute to the magnetic and magnetocaloric response of the system. The dilution effect of Al element on the FM Gd-Gd interaction is responsible for the decrease of the Curie temperature (TC), whereas the increase of the …
The phase transformation kinetics of LaFe$_{11.41}$Mn$_{0.30}$Si$_{1.29}$-H$_{1.65}$ magnetocaloric compound is addressed by low rate calorimetry experiments. Scans at 1 mK/s show that its first order phase transitions are made by multiple heat fllux avalanches. Getting very close to the critical point, the step-like discontinuous behavior associated with avalanches is smoothed out and thermal hysteresis disappears. This result is confirmed by magneto-resistivity measurements and allows to measure accurate values of the zero field hysteresis ($ΔT_{hyst}$ = 0.37 K) and of the critical field (H$…
The processing of promising magnetocaloric materials into spheres is one of the important issues on developing high-performance magnetic refrigeration systems. In the present study, we achieved in producing spherical particles of a giant magnetocaloric compound HoB2 by a crucible-free gas atomization process, despite its high melting point of 2350 C. The particle size distribution ranges from 100 to 710 micrometers centered at 212-355 micrometers with the highest yield of 14-20wt% of total melted electrode, which is suitable for magnetic refrigeration systems. The majority of the resulting par…
Inelastic neutron scattering measurements were performed on single crystals of the antiferromagnetic compound Mn5Si3 in order to investigate the relation between the spin dynamics and the magneto-thermodynamic properties. It is shown that among the two stable antiferromagnetic phases of this compound, the high temperature one has an unusual magnetic excitation spectrum where propagative spin-waves and diffuse spin-fluctuations coexist. Moreover, it is evidenced that the inverse magnetocaloric effect of Mn5Si3, the cooling by adiabatic magnetization, is associated with field induced spin-fluctu…
Magnetic ground state, critical analysis of magnetization, and large magnetocaloric effect in the ferromagnetically coupled kagome lattice YCa$_3$(MnO)$_3$(BO$_3$)$_4$
We present a thorough study on the magnetoanisotropic properties and magnetocaloric effect in the layered ferromagnetic Cr$_4$Te$_5$ single crystals by performing the critical behaviour analysis of magnetization isotherms. The critical exponents $β$=0.485(3), $γ$=1.202(5), and $δ$=3.52(3) with a Curie temperature of $T_C \approx 340.73(4)$ K are determined by the modified Arrott plots. We observe a large magnetocrystalline anisotropy K$_u$=330 kJ/$m^3$ at 3 K which gradually decreases with increasing temperature. Maximum entropy change -$ΔS_{M}^{max}$ and the relative cooling power (RCP) are f…
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 $H\parallel c$ axis and $H\parallel ab$ plane. We observed a significant (factor of $2$) difference between the magnetocaloric effect measured in both orientations. The rotating magnet…
The magnetocaloric effect (MCE) in many rare earth (RE) based intermetallic compounds has been extensively investigated during last two decades, not only due to their potential applications for magnetic refrigeration but also for better understanding of the fundamental problems of the materials. This paper reviews our recent progress of magnetic properties and MCE in some binary or ternary intermetallic compounds of RE with low boiling point metal(s) (Zn, Mg, and Cd). Some of them are exhibiting promising MCE properties which make them also attractive for low temperature magnetic refrigeration…
We report on the magnetic and magnetocaloric properties of a MnRhAs single crystal. The ternary arsenide exhibits a rather complex magnetic behaviour. A first order metamagnetic type transition from antiferromagnetic (AFI) to ferromagnetic (F) states takes place at Tt ~ 158 K, and a second order transition from ferromagnetic (F) to antiferromagnetic (AFII) states occurs at TC ~196 K, the paramagnetic state occurring at T > TN = 238 K. Magnetic entropy changes were calculated using, Maxwell relation and Clausius-Clapeyron equation. Both approaches are compared and discussed. The AFI-F transitio…
We compute the magnetocaloric effect (MCE) in the GdTX (T=Sc, Ti, Co, Fe; X=Si, Ge) compounds as a function of the temperature and the external magnetic field. To this end we use a density functional theory approach to calculate the exchange-coupling interactions between Gd$^{3+}$ ions on each compound. We consider a simplified magnetic Hamiltonian and analyze the dependence of the exchange couplings on the transition metal T, the p-block element X, and the crystal structure (CeFeSi-type or CeScSi-type). The most significant effects are observed for the replacements Ti $\to$ Sc or Fe $\to$ Co …
The compounds FeMnAsxP1-x are very promising as far as commercial applications of the magnetocaloric effect are concerned. However, the theoretical literature on magnetocaloric materials still adopts simple molecular-field models in the description of important properties like the entropy variation that accompanies applied isothermal magnetic field cycling, for instance. We apply a Green function theoretical treatment for such analysis. The advantages of such approach are well-known since the details of the crystal structure are incorporated in the model, as well as a precise description of co…
Perovskite manganite La0.5Ca0.5-x xMnO3 (LCMO) nanomaterials were elaborated using the sucrose modified auto combustion method. Rietveld refinements of the X-ray diffraction patterns of the crystalline structure confirm a single-phase orthorhombic state with Pbnm space group (No. 62). The Ca-vacancies were voluntarily created in the LCMO structure in order to study their influence on the magnetic behaviour in the system. The magnetic susceptibility was found to be highly enhanced in the sample with Ca-vacancies. Paramagnetic-to-ferromagnetic phase transition was evidenced in both samples aroun…
