It is known that the Zircon-type orthovanadates RVO4 show promise in many different applications as catalysts and optical materials. In this work, we demonstrate that the TbVO4 compound can be also used as magnetic refrigerant in efficient and ecofriendly cryocoolers due to its strong magnetocaloric effect at low temperature regime. The application of a relatively low magnetic field of 2 T along the easy magnetization axis (a) gives rise to a maximum entropy change of about 20 J/kg K at 4 K. More interestingly, under sufficiently high magnetic fields, the isothermal entropy change -ΔST remains approximately constant over a wide temperature range which is highly appreciated from a practical point of view. In the magnetic field change of 7 T, -ΔST that reaches roughly 22 J/kg K remains practically unchanged between 0 and 34 K leading to an outstanding refrigerant capacity of about 823 J/kg. On the other hand, the lowering of crystallographic symmetry from the tetragonal to the orthorhombic structure occurring close to 33 K as confirmed by Raman scattering data results in a strong magnetic anisotropy. Accordingly, strong thermal effects can be also obtained simply by spinning the TbVO4 single crystals between their hard and easy orientations in constant magnetic fields instead the standard magnetization-demagnetization process. Such rotating magnetocaloric effects would open the way for the implementation of TbVO4 in a new generation of compact and simplified magnetic refrigerators that can be dedicated to the liquefaction of hydrogen and helium.
Magnetic and magnetocaloric properties of high-purity, giant magnetocaloric polycrystalline and single-crystalline Fe2P are investigated. Fe2P displays a moderate magnetic entropy change which spans over 70 K and the presence of strong magnetization anisotropy proves this system is not fully itinerant but displays a mix of itinerant and localized magnetism. The properties of pure Fe2P are compared to those of giant magnetocaloric (Fe,Mn)2(P,A) compounds helping understand the exceptional characteristics shown by the latter which are so promising for heat pump and energy conversion applications…
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 thermodynamics of a site-diluted ferromagnetic Heisenberg model for spin $S=1/2$ with interaction anisotropy in spin space is investigated. The study is aimed at presenting the magnetocaloric properties of such a model, including the entropy and temperature changes in magnetization/demagnetization processes, generalized Grüneisen ratio as well as the quantities characterizing the efficiency of magnetic cooling cycles. The results are obtained using Pair Approximation (PA) method and extensively compared with the Molecular Field Approximation (MFA) calculations. The importance of interactio…
It is known that orthorhombic RMnO3 multiferroics (R = magnetic rare earth) with low symmetry exhibit a large rotating magnetocaloric effect because of their strong magnetocrystalline anisotropy. In this paper, we demonstrate that the hexagonal ErMnO3 single crystals also unveils a giant rotating magnetocaloric effect that can be obtained by spinning them in constant magnetic fields around their a or b axes. When the ErMnO3 crystal is rotated with the magnetic field initially parallel to the c-axis, the resulting entropy change reaches maximum values of 7, 17 and 20 J/kg K under a constant mag…
We present the results of a thorough study of the specific heat and magnetocaloric properties of a ludwigite crystal Cu2MnBO5 over a temperature range of 60 - 350 K and in magnetic fields up to 18 kOe. It is found that at temperatures below the Curie temperature (92 K), capacity possesses a linear temperature-dependent behavior, which is associated with the predominance of two-dimensional antiferromagnetic interactions of magnons. The temperature independence of capacity is observed in the temperature range of 95 - 160 K, which can be attributed to the excitation of the Wigner glass phase. The…
This work aims to present an analytical and numerical study of the magnetocaloric effects (MCE) providing realistic proposals about materials that should be chosen in the design of new refrigerator appliances around the room temperature. Starting from a spin Hamiltonian including the exchange interaction, the single-ion anisotropy and the applied magnetic field terms, we have calculated the partition function at a given temperature and derived a set of relevant physical quantities as magnetization, magnetic entropy and specific heat and analyzed their behavior with atomic parameters as spin, e…
We exploit the magnetic interlayer coupling in La0.7Sr0.3MnO3/SrRuO3 superlattices to realize a crossover between inverse and conventional magnetic entropy changes. Our data reveal a strong anisotropic nature of the magnetocaloric effect due to the magnetic anisotropy of the superlattice. Therefore, artificial superlattices built from ferromagnetic materials that can be used to alter the magnetic structure as well as the magnetic anisotropy, could also be utilized for tuning the magnetocaloric properties, which may open a constructive approach for magnetic refrigeration applications.
Solid state-refrigerants have generated worldwide interest owing to their growing potential for use in efficient and green cooling devices. Caloric effects could be obtained by manipulating their degrees of freedom such as magnetization, electric polarization and volume using a variable external field. In conventional magnetocaloric refrigeration systems, the magnetocaloric effect is exploited by moving the active material in and out of the magnetic field source. Here we demonstrate that a giant and reversible magnetocaloric effect can be generated simply by rotating the multiferroic TbMn2O5 s…
This work investigates the magnetic properties and the magnetocaloric effect in the spin-1 Blume-Capel model. The study was carried out using the mean-field theory from the Bogoliubov inequality to obtain the expressions of free energy, magnetization and entropy. The magnetocaloric effect was calculated from the variation of the entropy obtained by the mean-field theory. Due to the dependence on the external magnetic field and the anisotropy included in the model, the results for the magnetocaloric effect provided the system with first-order and continuous phase transitions. To ensure the resu…
An unusually large magnetocaloric effect for the temperature region below 10 K is found for the Fe14 molecular nanomagnet. This is to large extent caused by its extremely large spin S ground-state combined with an excess of entropy arising from the presence of low-lying excited S states. We also show that the highly symmetric Fe14 cluster core, resulting in small cluster magnetic anisotropy, enables the occurrence of long-range antiferromagnetic order below T_N=1.87 K.
The thermodynamics of a spin-1/2 magnetic multilayer system with antiferromagnetic interplanar couplings is studied using the Pair Approximation method. The special attention is paid to magnetocaloric properties, quantified by isothermal entropy change. The multilayer consists of two kinds of magnetic planes, one of which is diluted. The intraplanar couplings in both planes have arbitrary anisotropy ranging between Ising and isotropic Heisenberg interactions. The phase diagram related to the occurrence of magnetic compensation phenomenon is constructed and discussed. Then the isothermal entrop…
Based on high-throughput density functional theory calculations, we performed screening for stable magnetic MAB compounds and predicted potential strong magnets for permanent magnet and magnetocaloric applications. The thermodynamical, mechanical, and dynamical stabilities are systematically evaluated, resulting in 21 unreported compounds on the convex hull, and 434 materials being metastable considering convex hull tolerance to be 100 meV/atom. Analysis based on the Hume-Rothery rules revealed that the valence electron concentration and size factor difference are of significant importance in …
We present a comprehensive investigation on anisotropic magnetic and magnetocaloric properties of the quasi-two-dimensional weak itinerant ferromagnet trigonal Cr$_{0.62}$Te single crystals. Magnetic-anisotropy-induced satellite transition $T^*$ is observed at low fields applied parallel to the $ab$ plane below $T_c$. The $T^*$ is featured by an anomalous magnetization downturn, similar to that in structurally related CrI$_3$, and shows a monotonous shift towards lower temperature with increasing field. Magnetocrystalline anisotropy is also reflected in magnetic entropy change $ΔS_M(T,H)$ and …
Mechanical control of magnetic properties in magnetostrictive thin films offers the unexplored opportunity to employ surface wave acoustics in such a way that acoustic triggers dynamic magnetic effects. The strain-induced modulation of the magnetic anisotropy can play the role of a high frequency varying effective magnetic field leading to ultrasonic tuning of electronic and magnetic properties of nanostructured materials, eventually integrated in semiconductor technology. Here, we report about the opportunity to employ surface acoustic waves to trigger magnetocaloric effect in MnAs(100nm)/GaA…
A comparison of the spin-phonon behaviour of Fe$_2$P-based magnetocaloric materials
Uppsala University（乌普萨拉大学）；National Institute for Materials Science (NIMS)（国立材料研究所）；Institut Laue-Langevin（朗之万研究所）；Technische Universität München（慕尼黑工业大学）；Rutherford Appleton Laboratory（鲁瑟福阿普利顿实验室）；Oak Ridge National Laboratory（橡树岭国家实验室）；European Spallation Source ESS ERIC（欧洲散裂源）
In this manuscript, we propose a method to prepare small flakes of DyCu2. On top of that we also report on the magnetocaloric effect and nature of magnetic transition of a strongly anisotropic DyCu2 in its low dimension. Magnetization measurements were carried out in the temperature range of 5 to 100 K and up to the maximum magnetic field strength of 50 kOe. Magnetic entropy change delta SM is estimated using the well known Maxwells equations and is found to be 4.31 J per kg K. Indeed, the delta SM peak broadened marginally compared with its bulk DyCu2 and such a broadening can be attributed t…
ZrMnP and HfMnP single crystals are grown by a self-flux growth technique and structural as well as temperature dependent magnetic and transport properties are studied. Both compounds have an orthorhombic crystal structure. ZrMnP and HfMnP are ferromagnetic with Curie temperatures around $370$~K and $320$~K respectively. The spontaneous magnetizations of ZrMnP and HfMnP are determined to be $1.9$~$μ_\textrm{B}$/f.u. and $2.1$~$μ_\textrm{B}$/f.u. respectively at $50$~K. The magnetocaloric effect of ZrMnP in term of entropy change ($ΔS$) is estimated to be $-6.7$ kJm$^{-3}$K$^{-1}$ around $369$~…
The lanthanide orthoborates, $Ln$BO$_3$, $Ln$ = Gd, Tb, Dy, Ho, Er, Yb crystallise in a monoclinic structure with the magnetic $Ln^{3+}$ forming an edge-sharing triangular lattice. The triangles are scalene, however all deviations from the ideal equilateral geometry are less than 1.5%. The bulk magnetic properties are studied using magnetic susceptibility, specific heat and isothermal magnetisation measurements. Heat capacity measurements show ordering features at $T \leq$ 2 K for $Ln$ = Gd, Tb, Dy, Er. No ordering is observed for YbBO$_3$ at $T \geq$ 0.4 K and HoBO$_3$ is proposed to have a n…
Slow spin-lattice relaxation dynamics in YbVO4 revealed by extended thermal impedance spectroscopy from AC susceptibility and AC magnetocaloric measurements
Stanford University（斯坦福大学）；Geballe Laboratory for Advanced Materials, Stanford University（斯坦福大学先进材料盖伯勒实验室）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）
High-throughput density functional calculations are used to investigate the effect of interstitial B, C and N atoms on 21 alloys reported to crystallize in the cubic Cu$_3$Au structure. It is shown that the interstitials can have a significant impact on the magneto-crystalline anisotropy energy (MAE), the thermodynamic stability and the magnetic ground state structure, making these alloys interesting for hard magnetic, magnetocaloric and other applications. For 29 alloy/interstitial combinations the formation of stable alloys with interstitial concentrations above 5\% is expected. In Ni$_3$Mn …
We report the magnetization ($M$) and magnetoresistance (MR) results of HoAl$_2$ single crystals oriented along $<100>$ and $<110>$ directions. Although HoAl$_2$ has cubic Laves phase structure, a large anisotropy is observed in $M$ and MR results below Curie temperature ($T_C$) at 31.5 K. A satisfactory correlation between magnetic entropy change ($ΔS_M$) and MR could be established along $<110>$ direction and in $<100>$ direction except for the temperature ($T$) region, around which spin reorientation takes place. Large inverse magnetocaloric effect is observed at low-$T$ which is associated…
We report thermal expansion measurements carried out on a single-crystal of the giant magnetocaloric effect material Gd5(Si0.43Ge0.57)4. At the magneto-structural phase transition at T_0 ~ 240 K, large steps in the relative length change DELTAL/L along the principle crystallographic axes are observed. The single-step behaviour in DELTAL/L indicates that the magnetic and structural phase transition occur at one and the same temperature. The specific heat was measured in order to determine the latent heat. Using the Clausius-Clapeyron relation we extract a hydrostatic pressure dependence dT_0/dp…
A systematic study of the structural and magnetic properties of three-dimensionally frustrated lanthanide garnets $Ln_3A_2X_3\text{O}_{12}$, $Ln$ = Gd, Tb, Dy, Ho, $A$ = Ga, Sc, In, Te, $X$ = Ga, Al, Li is presented. Garnets with $Ln$ = Gd show magnetic behaviour consistent with isotropic Gd$^{3+}$ spins; no magnetic ordering is observed for T $\geq$ 0.4 K. Magnetic ordering features are seen for garnets with $Ln$ = Tb, Dy, Ho in the temperature range 0.4 < T < 2.5 K, however the nature of the magnetic ordering varies for the different $Ln$ as well as for different combinations of $A$ and $X$.…
Based on density functional theory calculations, we elucidated the origin of multifunctional properties for cubic antiperovskites with noncollinear magnetic ground states, which can be attributed to strong isotropic and anisotropic magnetostructural coupling. 16 out of 54 stable magnetic antiperovskites M$_3$XZ (M = Cr, Mn, Fe, Co, and Ni; X = selected elements from Li to Bi except for noble gases and 4f rare-earth metals; and Z = C and N) are found to exhibit the $Γ_{4g}$/$Γ_{5g}$ (i.e., characterized by irreducible representations) antiferromagnetic magnetic configurations driven by frustrat…
Magnetic properties of a buckled honeycomb lattice antiferromagnet
Indian Institute of Technology Madras（印度马德拉斯理工学院）；Quantum Centre of Excellence for Diamond and Emergent Materials, Indian Institute of Technology Madras（印度马德拉斯理工学院量子卓越中心（钻石与新兴材料））
Besides being a fascinating class of new materials, magnetic molecules provide the opportunity to study concepts of condensed matter physics in zero dimensions. This contribution will exemplify the impact of molecular magnetism on concepts of frustrated spin systems. We will discuss spin rings and the unexpected rules that govern their low-energy behavior. Rotational bands, which are experimentally observed in various molecular magnets, provide a useful, simplified framework for characterizing the energy spectrum, but there are also deviations thereof with far-reaching consequences. It will be…
Exchange bias-like effect observed in the intermetallic compound TbFeAl, which displays a magnetic phase transition at $T^h_c \approx$ 198~K and a second one at $T^l_c \approx$ 154~K, is reported. {\em Jump}-like features are observed in the isothermal magnetization, $M (H)$, at 2~K which disappear above 8~K. The field-cooled magnetization isotherms below 10~K show loop-shifts that are reminiscent of exchange bias, also supported by {\em training effect}. Significant coercive field, $H_c \approx$ 1.5~T at 2~K is observed in TbFeAl which, after an initial increase, shows subsequent decrease wit…
