La(Fe,Si)13-based magnetic refrigerants obtained by novel processing routes

The structure and magnetic properties of LaFe_13−xSi_x and Co-substituted LaFe_11.8−xCo_xSi_1.2 alloys prepared by melt spinning, as well as of LaFe_11.57Si_1.43H_x hydrides prepared by reactive milling are investigated. The hysteresis in the temperature- and field-induced phase transitions is significantly reduced as compared with conventional bulk alloys, which makes these materials very attractive for magnetic refrigerant applications. The unusual combination of features characteristic of first- and second-order phase transitions in the La(Fe,Si)₁₃-based compounds is discussed on the basis of density-functional electronic structure calculations.     

La(Fe,Si)13-based magnetic refrigerants obtained by novel processing routes

The structure and magnetic properties of LaFe_13−xSi_x and Co-substituted LaFe_11.8−xCo_xSi_1.2 alloys prepared by melt spinning, as well as of LaFe_11.57Si_1.43H_x hydrides prepared by reactive milling are investigated. The hysteresis in the temperature- and field-induced phase transitions is significantly reduced as compared with conventional bulk alloys, which makes these materials very attractive for magnetic refrigerant applications. The unusual combination of features characteristic of first- and second-order phase transitions in the La(Fe,Si)₁₃-based compounds is discussed on the basis of density-functional electronic structure calculations.     

Fermi surface properties of CeRu2(Si1-xGex)2 in magnetic fields above the metamagnetic transitions

We report de Haas-van Alphen effect measurements on CeRu2(Si(1-x)Gex)2 to reveal electronic structure change over the broad range of chemical pressure from x=0.0 to 1.0. It is found that the Fermi surface properties change drastically across the metamagnetic crossover field (B(m)) but vary smoothly with x from those in magnetic fields above B(m) in CeRu2Si2 to those in the ferromagnetic state in CeRu2Ge2. Implications of the present results are discussed in conjunction with the magnetic phase diagram.     

Effect of hydrostatic pressure on the magnetic and lattice properties of the ferromagnet La(Fe0.86Si0.14)13

The temperature dependence of the lattice constant of the ferromagnet La(Fe_0.86Si_0.14)₁₃ has been measured at different pressures and temperatures. The numerical value of the bulk modulus at room temperature has been determined. The measurements of the temperature dependence of the lattice constant of the ferromagnet La(Fe_0.86Si_0.14)₁₃ at zero pressure and at 11.5 kbar have demonstrated that, at zero pressure, the lattice constant sharply decreases in the range from 160 to 210 K, whereas at a pressure of 11.5 kbar, the lattice constant decreases in the range from 110 to 180 K. This indicates that the Curie temperature T _C changes from 210 to ～170 K under pressure. The experimental results have been analyzed using the equations of states for the magnetic and elastic subsystems of the ferromagnet.     

Effects of interstitial H and/or C atoms on the magnetic and magnetocaloric properties of La(Fe, Si)13-based compounds

La(Fe, Si)₁₃-based compounds have been considered as promising candidates for magnetic refrigerants particularly near room temperature. Herein we review recent progress particularly in the study of the effects of interstitial H and/or C atoms on the magnetic and magnetocaloric properties of La(Fe, Si)₁₃ compounds. By introducing H and/or C atoms, the Curie temperature T _C increases notably with the increase of lattice expansion which makes the Fe 3d band narrow and reduces the overlap of the Fe 3d wave functions. The first-order itinerant-electron metamagnetic transition is conserved and the MCE still remains high after hydrogen absorption. In contrast, the characteristic of magnetic transition varies from first-order to second-order with the increase of C concentration, which leads to remarkable reduction of thermal and magnetic hysteresis. In addition, the introduction of interstitial C atoms promotes the formation of NaZn₁₃-type (1:13) phase in La(Fe, Si)₁₃ compounds, and thus reducing the annealing time significantly from 40 days for LaFe_11.7Si_1.3 to a week for LaFe_11.7Si_1.3C_0.2. The pre-occupied interstitial C atoms may depress the rate of hydrogen absorption and release, which is favorable to the accurate control of hydrogen content. It is found that the reduction of particle size would greatly depress the hysteresis loss and improve the hydrogenation process. By the incorporation of both H and C atoms, large MCE without hysteresis loss can be obtained in La(Fe, Si)₁₃ compounds around room temperature, for instance, La_0.7Pr_0.3Fe_11.5Si_1.5C_0.2H_1.2 exhibits a large |ΔS _M| of 22.1 J/(kg·K) at T _C = 321 K without hysteresis loss for a field change of 0–5 T.     

Asymmetric first‐order transition and interlocked particle state in magnetocaloric La(Fe,Si)13

In‐situ synchrotron XRD measurements of the magnetocaloric material LaFe_11.8Si_1.2 are used to understand virgin effects and asymmetry of the underlying first order magnetovolume transition. A remarkable change of the transition kinetics occurs after the first cycle, which we attribute to the formation of cracks originating from the volume change. Tomographic imaging revealed that the bulk material disintegrates via an interlocked state where fragments are loosely connected. Though cracks have opened between the fragments, the transition is sharp, which we attribute to magnetostatic interactions. In the cycled sample we find a strong asymmetry between the transition interval upon heating and cooling, which we explain by isostatic pressure acting on parts of the sample during the cooling transition. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Field-induced magnetic transitions in Pr2(Co,Fe)17

A study of the different magnetic field-induced transitions has been performed for Pr₂Co_17−xFe_x compounds in the temperature range 78–300 K. By using the singular point detection technique, it has been shown that all compounds with x>0 exhibit at least one field-induced transition, which has been identified as a first-order magnetization process (FOMP). Different types of FOMP (A1, A2, P1) are observed, and the change of the type can be induced by varying either temperature or composition. Intermediate Co–Fe compositions show a P1-type FOMP which persists even above room temperature, while a double transition has been found in iron-rich compounds with x⩾13.6. It has also been noticed that, for the particular values of x when a temperature-induced spin reorientation is present, the change from A1 to P1 type FOMP (or vice versa) exactly occurs at the spin reorientation temperature, with a vanishing critical field value. A comparison with the behavior of Y₂Co_17−xFe_x compounds leads to the conclusion that the contributions of the Pr sublattice are essential for the development of these field-induced transitions (some of which are still present at room temperature), even if it is inferred that the overall anisotropy is mainly determined by the 3d sublattice.     

Properties of magnetocaloric La(Fe,Co,Si)13 produced by powder metallurgy

We present a comprehensive study of the magnetocaloric materials series La(Fe_1−xCo_x)_11.9Si_1.1 with 0.055<x<0.122. The ferromagnetic samples were manufactured using a novel powder metallurgy process by which industrial scale production is feasible. This new production method makes the materials more attractive as magnetic refrigerants for room temperature magnetic refrigeration. The Curie temperature of the compounds can be easily tuned by altering the Co content and all samples have little magnetic anisotropy and present a second-order magnetic transition so that thermal and magnetic hysteresis is absent. For all seven samples, we have calculated the magnetic entropy change, ΔS_M, from initial curve measurements and measured the adiabatic temperature change, ΔT_ad, directly. In addition, for two of the samples, we determined the heat capacity as a function of applied magnetic field and the thermal conductivity. Where relevant, the results are compared with those of Gd, the benchmark material for room temperature magnetic refrigeration.     

Machine learning technique for prediction of magnetocaloric effect in La(Fe,Si/Al)_(13)-based materials

Data-mining techniques using machine learning are powerful and efficient for materials design, possessing great potential for discovering new materials with good characteristics. Here, this technique has been used on composition design for La(Fe,Si/Al)_(13)-based materials, which are regarded as one of the most promising magnetic refrigerants in practice. Three prediction models are built by using a machine learning algorithm called gradient boosting regression tree(GBRT) to essentially find the correlation between the Curie temperature(T_C), maximum value of magnetic entropy change((?S_M)_(max)),and chemical composition, all of which yield high accuracy in the prediction of T_C and(?SM)_(max). The performance metric coefficient scores of determination(R~2) for the three models are 0.96, 0.87, and 0.91. These results suggest that all of the models are well-developed predictive models on the challenging issue of generalization ability for untrained data, which can not only provide us with suggestions for real experiments but also help us gain physical insights to find proper composition for further magnetic refrigeration applications.     

Magnetic behaviour of the cubic La(Fe,Al)13 compounds

The magnetic properties of the cubic NaZn₁₃ type pseudobinary compounds LaFe_XAl_13–x were studied in the temperature range T=4.2–300 K by means of⁵⁷Fe-Mössbauer spectroscopy, magnetization and zero-field susceptibility measurements. The compounds LaFe_xAl_13–x show a rather peculiar concentration dependence of the type of magnetic ordering as well as of the ordering temperature.     

Simulation of the magnetic and magnetocaloric properties of hydrides of the La(Fe0.88Si0.12)13 compound by applying a negative pressure

Based on the model calculation, it has been shown that the effect of hydration of the ferromagnetic compounds La(Fe_0.88Si_0.12)₁₃H _y is quantitatively adequately described by the introduction of a negative pressure. The calculations have been performed for compounds with hydrogen concentrations y = 0, 0.5, 1.0, and 1.5. It has been found that these concentrations correspond to the pressures P = 0, ?0.95, ?1.85, and ?2.80 GPa, respectively. The calculated Curie temperature, magnetization, characteristics of the magnetocaloric effect, and other properties are in satisfactory agreement with experiment.     

Erratum to: Multiple magnetic transitions in single crystals of Ce12Fe57.5As41and La12Fe57.5As41

Commercial computers based on electronic logic devices have brought great changes to the world. However, traditional electronic devices are suffering from numerous technical challenges in their attempts to continue to satisfy Moore's law. Alloptical logic devices, as promising successors to their electronic counterparts, have become a major focus of optics research. In this paper, we provide a review of current all-optical logic devices. The logic gates in these devices, which are described in the first part of the review, are divided into five categories based on the different principles used in their realization. Complex optical devices with various functions and reconfigurable devices are summarized in the next section. In the final part of this paper, we discuss some of the previous works on all-optical integrated chips with specific functions. This review will provide a complete technological roadmap for all-optical devices and aims to be helpful in possible future developments in this growing field.     

GREAT MAGNETIC ENTROPY CHANGE IN La(Fe, M)13 (M=Si, Al) WITH Co DOPING

Very large magnetic entropy change Δ S_M, which originates from a fully reversible second-order transition at Curie temperature T_C, has been discovered in compounds La(Fe, Si)₁₃, La(Fe, Al)₁₃ and those with Co doping. The maximum change ΔS_M\approx19 J·kg^-1·K^-1, achieved in LaFe_11.4Si_1.6 at 209K upon a 5T magnetic field change, exceeds that of Gd by more than a factor of 2. The T_C of the Co-doped compounds shifts to higher temperatures. ΔS_M still has a considerable large magnitude near room temperature. The phenomena of very large ΔS_M, convenience of adjustment of T_C, and also thesuperiority of low cost, strongly suggest that the compounds La(Fe, M)₁₃ (M=Si, Al) with Co doping are suitable candidates for magnetic refrigerants at high temperatures.     

Magnetic properties and magnetocaloric effects in NaZn13-type La（Fe, Al）13-based compounds

In this article,our recent progress concerning the effects of atomic substitution,magnetic field,and temperature on the magnetic and magnetocaloric properties of the LaFe13-xAlx compounds are reviewed.With an increase of the aluminum content,the compounds exhibit successively an antiferromagnetic(AFM) state,a ferromagnetic(FM) state,and a mictomagnetic state.Furthermore,the AFM coupling of LaFe 13-xAlx can be converted to an FM one by substituting Si for Al,Co for Fe,and magnetic rare-earth R for La,or introducing interstitial C or H atoms.However,low doping levels lead to FM clusters embedded in an AFM matrix,and the resultant compounds can undergo,under appropriate applied fields,first an AFM-FM and then an FM-AFM phase transition while heated,with significant magnetic relaxation in the vicinity of the transition temperature.The Curie temperature of LaFe13-xAlx can be shifted to room temperature by choosing appropriate contents of Co,C,or H,and a strong magnetocaloric effect can be obtained around the transition temperature.For example,for the LaFe 11.5Al1.5C0.2H1.0 compound,the maximal entropy change reaches 13.8 J·kg-1 ·K-1 for a field change of 0-5 T,occurring around room temperature.It is 42% higher than that of Gd,and therefore,this compound is a promising room-temperature magnetic refrigerant.     

Magnetization behavior and metamagnetic transitions in electron-doped manganites induced by a strong magnetic field

The behavior of magnetization M of the R_xA_1?xMnO₃ manganites (R=La, Pr, Nd, Sm, etc., A=Ca, Sr, Ba) in the electron doping region (x<0.4) is studied as a function of external magnetic field H. The M(H) relations for homogeneous magnetic structures are obtained by performing band calculations in the double-exchange model. Three different types of magnetization behavior corresponding to three electron concentration ranges (x<0.14, 0.14<x<0.27, x>0.27) are revealed. The M(H) relations are interpreted in terms of the phase diagram for the homogeneous ground state of the manganites calculated for H=0, and the results agree qualitatively with experimental data on the magnetization of Sm_xCa_1?xMnO₃.     

Quenching of giant hysteresis effects in La(1-z)Y(z)Hx switchable mirrors

Hydrogen atoms adsorbed on TiO2(110)-(1x1) surfaces have been characterized by scanning tunneling microscopy (STM) combined with electron stimulated desorption (ESD) technique. Certain amounts of H atoms are unexpectedly found on the TiO2 surfaces annealed at 900 K. Two forms of adsorption were discriminated in STM images from the different sensitivity to ESD and tentatively assigned to hydroxyl-type (O-H) and hydride-type (Ti-H) species.     

Y(Fe,M)12化合物的电子结构与磁性(M=Nb,Si)

采用新近发展的全势能线性缀加平面波((L)APW) 局域轨道(lo)和广义梯度近似(GGA)密度泛函方法计算了Y(Fe,M)12化合物(M=Nb,Si)的电子结构,得到了相应的总态密度和局域态密度,并分析了替代原子与替代晶位不同引起态密度的变化。根据计算结果预测的居里温度变化与实验结果基本一致。