Magnetostriction and spin reorientation in ferromagnetic Laves phase Pr(Ga_xFe_(1-x))_(1.9) compounds

The magnetostriction, magnetization, and spin reorientation properties in Pr(Ga_xFe_(1-x))_(1.9) alloys have been investigated by high-precision x-ray diffraction(XRD) step scanning, magnetization, and Mo¨ssbauer spectra measurements. Ga substitution reduces the magnetostriction(λ_(||)) with magnetic field H ≥ 8 kOe(1 Oe = 1.33322×10~2 Pa), but it also increases the λ|| value when H ≤ 8 kOe at 5 K. Spin-reorientations(SR) are observed in all the alloys investigated, as determined by the step scanned XRD, Mo¨ssbauer spectra, and the abnormal temperature dependence of magnetization. An increase of the spin reorientation temperature(T_(SR)) due to Ga substitution is found in the phase diagram, which is different from the decrease one in many R(T_x Fe_(1-x))_(1.9)(T = Co, Al, Mn) alloys. The present work provides a method to control the easy magnetization direction(EMD) or T_(SR) for developing an anisotropic compensation system.     

Substituting Al for Fe in Pr(Al_xFe_(1-x))_(1.9) alloys:Effects on magnetic and magnetostrictive properties

The magnetostrictive effects of substituting Al for Fe in Pr(AlxFe1-x)1.9(x = 0.0, 0.02, 0.05, 0.10) alloys between5 K and 300 K were investigated. The substitution decreases the Curie temperature and the value of λ111. Fortunately, the substitution slightly increases the magnetostriction in a low magnetic field, which imbues these materials with potential advantages for applications. Rotation of the easy magnetization direction(EMD) from [111] to [100] in the Pr(Al0.02Fe0.98)1.9alloy as temperature decreases was detected by step scanned XRD reflections.     

Dy substitution effect on the temperature dependences of magnetostriction in Pr_(1-x)Dy_xFe_(1.9) alloys

The temperature dependences of magnetostriction in Pr_(1 x)Dy_xFe_(1.9)(0 ≤ x ≤ 1.0) alloys between 5 K and 300 K were investigated.An unusual decrease of magnetostriction with temperature decreasing was found in Pr-rich alloys(0 ≤x≤ 0.2),due to the change of the easy magnetization direction(EMD).Dy substitution reduces the magnetostriction in high-magnetic field(10 kOe ≤ H≤90 kOe) at 5 K,while a small amount of Dy substitution(x = 0.05) is beneficial to increasing the magnetostriction in low-magnetic field between 10 K and 50 K.This makes the alloys a potential candidate for low temperature applications.     

Magnetic properties and magnetostriction of PrxNd1-xFe1.9 (0≤x≤1.0) alloys at low temperature

The crystal structure, magnetic and magnetostrictive properties of high-pressure synthesized Pr_xNd_1-xFe_1.9 (0≤x≤1.0) alloys were studied. The alloys exhibit single cubic Laves phase with MgCu₂-type structure. The initial magnetization curve reveals that Pr_0.2Nd_0.8Fe_1.9 has a minimum magnetocrystalline anisotropy at 5 K. The magnetostriction curve at 5 K shows that Pr_0.2Nd_0.8Fe_1.9 has a very good low-field magnetostrictive property, and the magnetostriction of the Pr_xNd_1-xFe_1.9 alloy in high magnetic field is attributable mainly to Pr. The temperature dependence of the magnetostriction (λ_||) at the field of 5 kOe shows that the substitution of Nd reduces the K₁ remarkably, and the values of λ_|| of Pr_0.2Nd_0.8Fe_1.9 and Pr_0.8Nd_0.2Fe_1.9 alloys are nearly five times larger than that of PrFe_1.9 alloy below 50 K; the λ_|| of Pr_0.8Nd_0.2Fe_1.9 reaches up to 1082 ppm at 100 K, which makes it a potential candidate for application in this temperature range.     

First-principles calculations of structural,electronic, and thermodynamic properties of ZnO_(1-x)S_x alloys

In this study the pseudo-potential method is used to investigate the structural, electronic, and thermodynamic proper- ties of ZnOl_xSx semiconductor materials. The results show that the electronic properties are found to be improved when calculated by using LDA ~ U functional as compared with local density approximation （LDA）. At various concentrations the ground-state properties are determined for bulk materials ZnO, ZnS, and their tertiary alloys in cubic zinc-blende phase. From the results, a minor difference is observed between the lattice parameters from Vegard＇s law and other calculated results, which may be due to the large mismatch between lattice parameters of binary compounds ZnO and ZnS. A small deviation in the bulk modulus from linear concentration dependence is also observed for each of these alloys. The ther- modynamic properties, including the phonon contribution to Helmholtz free energy △F, phonon contribution to internal energy △E, and specific iheat at constant-volume Cv, are calculated within quasi-harmonic approximation based on the calculated phonon dispersion relations.     

(Nd_(1-x)Er_x)_2Co_(15.5)V_(1.5)的结构转变与磁性

利用电弧熔炼制备了 (Nd1 xErx) 2 Co1 5 5V1 5(x=0— 1 0 )化合物样品 .通过x射线衍射分析和磁性测量研究了Er替代Nd2 Co1 5 5V1 5中的Nd时对化合物结构和磁性的影响 .研究结果表明 ,低Er含量 (x <0 4 ) ,化合物为Th2 Zn1 7型结构 ;高Er含量时 (x >0 5 ) ,化合物转变为Th2 Ni1 7结构 ;Er含量为x =0 4和 0 5时 ,两种结构共存 .两种结构的晶胞参数a ,c和晶胞体积V随着Er含量的增加都呈现递减的趋势 .随着Er含量的增加 ,(Nd1 xErx) 2 Co1 5 5V1 5化合物的居里温度和饱和磁化强度都单调下降 .(Nd1 xErx) 2 Co1 5 5V1 5化合物的室温各向异性由低Er含量时的易锥型转变为高Er含量时的易轴型 .x =0— 0 5的化合物在温度升高时发生自旋重取向转变 ,自旋重取向温度Tsr随Er含量的增加而减小     

Magnetic properties and magnetocaloric effects in(Ho_(1-x)Y_x)_5Pd_2 compounds

The crystal structure, magnetic and magnetocaloric properties of(Ho_(1-x) Y_(0.5))_5 Pd_2 compounds are investigated. All the compounds crystallize in a cubic Dy_5 Pd_2-type structure with the space group Fd3 m and undergo a second order transition from spin glass(SG) state to paramagnetic(PM) state. The spin glass transition temperatures T_g decrease from 26 K for x = 0 to 13 K for x = 0.5. In the PM region, the reciprocal susceptibilities for all the compounds obey the Curie–Weiss law. The paramagnetic Curie temperatures(θp) for Ho_5 Pd_2,(Ho_(0.75) Y_(0.25)_5 Pd_2, and(Ho_(0.5) Y_(0.5))_5 Pd_2 are determined to be 32 K, 30 K, and 22 K, respectively, and the corresponding effective magnetic moments(μeff) are10.8 μB/Ho, 10.3 μB/RE, and 7.5 μB/RE, respectively. Magnetocaloric effect(MCE) is anticipated according to the Maxwell relation, based on the isothermal magnetization curves. For a magnetic field change of 0–5 T, the maximum values of the isothermal magnetic entropy change-?SMof the(Ho_(1-x)Y_x)_5 Pd_2(x = 0, 0.25, and 0.5) compounds are determined to be 11.5 J·kg~(-1)·K~(-1), 11.1 J·kg~(-1)·K~(-1), and 8.9 K J·kg~(-1)·K~(-1), with corresponding refrigerant capacity values of 382.3 J·kg~(-1), 336.2 J·kg~(-1), and 242.5 J·kg~(-1), respectively.     

Er_xY_(1-x)Al_3(BO_3)_4晶体的生长和光谱性质

采用助熔剂法生长出了掺杂均匀的Er_xY_(1-X)Al_3(BO_3)_4厘米级优质单晶.测定了晶体的吸收、激发光谱.用Judd_Ofelt理论计算了晶体中Er~(3+)的十一条谱带的振子强度(ρ_(ad)和ρ_(md)以及Er~(3+)的强度参数Q_λ(λ-2、4、6).并由此计算了Er~(3+)不同能级之间跃迁的爱因斯坦自发辐射系数A_r、辐射寿命r、荧光分支比β_3以及积分发射截面Σ.根据这些参数讨论了在EYAB晶体中可能实现激光输出的通道.     

First-principles calculations of structural and electronic properties of Tl_xGa_(1-x)As alloys

The zincblende ternary alloys Tl_xGa_(1-x) As(0 x 1) are studied by numerical analysis based on the plane wave pseudopotential method within the density functional theory and the local density approximation. To model the alloys,16-atom supercells with the 2 × 2 × 2 dimensions are used and the dependency of the lattice parameter, bulk modulus,electronic structure, energy band gap, and optical bowing on the concentration x are analyzed. The results indicate that the ternary Tl_xGa_(1-x) As alloys have an average band gap bowing parameter of 4.48 eV for semiconductor alloys and 2.412 eV for semimetals. It is found that the band gap bowing strongly depends on composition and alloying a small Tl content with GaAs produces important modifications in the band structures of the alloys.     

Coexistence of positive and negative magnetic entropy changes in CeMn_2(Si_(1-x)Ge_x)_2 compounds

A series of CeMn2(Si1-xGex)2(x = 0.2, 0.4, 0.6, 0.8) compounds are prepared by the arc-melting method. All the samples primarily crystallize in the Th Cr2Si2-type structure. The temperature dependences of zero-field-cooled(ZFC) and FC magnetization measurements show a transition from antiferromagnetic(AFM) state to ferromagnetic(FM) state at room temperature with the increase of the Ge concentration. For x = 0.4, the sample exhibits two kinds of phase transitions with increasing temperature: from AFM to FM and from FM to paramagnetic(PM) at around TN~197 K and T C~300 K,respectively. The corresponding Arrott curves indicate that the AFM–FM transition is of first-order character and the FM–PM transition is of second-order character. Meanwhile, the coexistence of positive and negative magnetic entropy changes can be observed, which are corresponding to the AFM–FM and FM–PM transitions, respectively.     

Structural and magnetic properties of BiFe_(1-x)Cr_xO_3 synthesized samples

Chromium doping effects on the structure and the magnetic properties of bismuth ferrite BiFe1-xCrxO3 （x = 0-0.3） （BFCxO） polycrystalline samples are examined. The Perovskite-type oxide samples are synthesized by the conventional solid state reaction at a high pressure of 7 GPa and a temperature of 1273 K. The X-ray powder diffraction patterns at room temperature show that all the samples with x = 0.0-0.3 are described by the rhombohedral structure. In the meantime, it is revealed that the doping of Cr can induce noticeable lattice distortions in the doping samples, and the largest distortion is observed in the case x = 0.1. The magnetic hysteresis loops measured at room temperature exhibit week ferromagnetic behaviors of the samples and the magnetization is found to increase with the increase in Cr concentration. The temperature- dependent magnetization curves indicate antiferromagnetic features in samples. Moreover, Cr-doping tends to reduce the ordering temperature.     

Effects of Pr substitution on the hydrogenating process and magnetocaloric properties of La_(1-x)Pr_xFe_(11.4)Si_(1.6)H_y hydrides

In this paper, we study the effects of Pr substitution on the hydrogenating process and magnetocaloric properties of La_(1-x)Pr_xFe_(11.4)Si_(1.6)H_y hydrides. The powder x-ray diffraction patterns of the La_(1-x)Pr_xFe_(11.4)Si_(1.6) and its hydrides show that each of the alloys is crystallized into the single phase of cubic Na Zn_(13)-type structure. There are hydrogen-absorbing plateaus under 0.4938 MPa and 0.4882 MPa in the absorbing curves for the La_(0.8)Pr_(0.2)Fe_(11.4)Si_(1.6) and La_(0.6)Pr_(0.4)Fe_(11.4)Si_(1.6) compounds. The releasing processes lag behind the absorbing process, which is obviously different from the coincidence between absorbing and releasing curves of the La Fe_(11.4)Si_(1.6) compound. The remnant hydrogen content for La_(0.6)Pr_(0.4)Fe_(11.4)Si_(1.6) is significantly more than that for La_(0.8)Pr_(0.2)Fe_(11.4)Si_(1.6) after hydrogen desorption, indicating that more substitutions of Pr for La are beneficial to retaining more hydrogen atoms in the alloys. The values of maximum magnetic entropy change are 14.91 J/kg·K and 17.995 J/kg·K for La_(0.8)Pr_(0.2)Fe_(11.4)Si_(1.6)H_(0.13) and La_(0.6)Pr_(0.4)Fe_(11.4)Si_(1.6)H_(0.87),respectively.     

(Nd1－xErx)2Co15.5V1.5的结构转变与磁性

利用电弧熔炼制备了(Nd1-xErx)2Co15.5V1.5（x=0—1.0）化合物样品.通过x射线衍射分析和磁性测量研究了Er替代Nd2Co15.5V1.5中的Nd时对化合物结构和磁性的影响.研究结果表明，低Er含量（x<0.4），化合物为Th2Zn17型结构；高Er含量时(x>0.)，化合物转变为Th2Ni17结构；Er含量为x＝0.4和0.5时，两种结构共存.两种结构的晶胞参数a,c和晶胞体积V随着Er含量的增加都呈现递减的趋势.随着Er含量的增加，(Nd1-xErx)2Co15.5V1.5化合物的 关键词： (Nd1-xErx)2Co15.5V1.5 结构转变 磁性     

Structure, spin reorientation and M(o)ssbauer effect studies of Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys

The effect of Al substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature and 77 K was investigated systematically. It was found that the primary phase of Tb0.3Dy0.7(Fe1-xAlx)1.95 is the MgCu2-type cubic Laves phase structure when x < 0.4 and the lattice constant a of Tb0.3Dy0.7(Fe1-xAlx)1.95 increases approximately and monotonically with the increase of x. The substitution of Al leads to the fact that the magnetostriction ( inceases slightly in a low magnetic field (H ≤ 40 kA/m), but decreases sharply and is easily close to saturation in a high applied field as x increases, showing that a small amount of Al substitution is beneficial to a decrease in the magnetocrystalline anisotropy. It was also found that the spontaneous magnetostriction (ζ)111 decreases greatly with x increasing. The analysis of the M(o)ssbauer spectra indicated that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry with the changes of composition and temperature, namely spin reorientation. A small amount of non-magnetic phase exists for x = 0.15 in Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys and the alloys become paramagnetic for x > 0.15 at room temperture, but at 77 K the alloys still remain magnetic phase even for x = 0.2. At room temperature and 77 K, the hyperfine field decreases and the isomer shifts increase with Al concentration increasing.     

Structure and magnetostrictive properties of melt-spun Pr(Fe0.4Co0.6)1.93 alloys

Pr(Fe_0.4Co_0.6)_1.93 ribbons were prepared by a melt-spinning method. Their structure and magnetic properties are investigated as functions of wheel speed and annealing temperature. The as-spun ribbon consists of a Pr(Fe, Co)₂ cubic Laves phase and an amorphous phase at a wheel speed of v≥35 m/s, while the non-cubic phases of PuNi₃-type and rare earth appear when the speed lower than 30 m/s. A single Pr(Fe, Co)₂ phase with MgCu₂-type structure has been synthesized by the process for the wheel speed of v≥35 m/s and subsequent annealing at 500 °C for 30 min. The epoxy/Pr(Fe_0.4Co_0.6)_1.93 composite has been produced by a cold isostatic pressing technique, and the magnetic properties have been investigated. The composite rod sample possesses good magnetostrictive properties, i.e., a large magnetostriction (λ_a=λ_∥−λ_⊥) of 710 ppm at 800 kA/m and a dynamic coefficient d₃₃ of 0.67 nm/A at 100 kA/m, and is of practical value.     

Abnormal variation of magnetic properties with Ce content in(PrNdCe)_2Fe_(14)B sintered magnets prepared by dual alloy method

Resource-saving(PrNdCe)_2Fe_(14)B sintered magnets with nominal composition(PrNd)_(15-x)Ce_xFe_(77)B_8(x=0–10)were prepared using a dual alloy method by mixing(PrNd)_5Ce_(10)Fe_(77)B_8 with(PrNd)_(15)Fe_(77)B_8 powders. For Ce atomic percent of 1% and 2%, coercivity decreases dramatically. With further increase of Ce atomic percent, the coercivity increases, peaks at 6.38 kOe in(PrNd)_(11)Ce_4Fe_(77)B_8, and then declines gradually. The abnormal dependence of coercivity is likely related to the inhomogeneity of rare earth chemical composition in the intergranular phase, where Pr Nd concentration is strongly dependent on the additive amount of(PrNd)_5Ce_(10)Fe_(77)B_8 powders. In addition, for Ce atomic percent of 8%,7%, and 6% the coercivity is higher than that of magnets prepared by the conventional method, which shows the advantage of the dual alloy method in preparing high abundant rare earth magnets.     

Irreversible metamagnetic transition and magnetic memory in small-bandwidth manganite Pr(1-x)Ca(x)MnO3 (x = 0.0-0.5)

The present paper reports detailed structural and magnetic characterization of the low-bandwidth manganite Pr(1-x)Ca(x)MnO(3) (with x = 0.0-0.5) (PCMO) polycrystalline samples. With increasing Ca content, reduction of the unit cell volume and improvement in perovskite structure symmetry was observed at room temperature. Magnetic characterization shows the signature of coexisting AFM-FM ordering and spin-glass phase at the low doping range (x = 0.0-0.2) while increased hole doping (x = 0.3-0.5) leads to charge ordering, training effect and an irreversible metamagnetic phenomenon. The large irreversible metamagnetism in the CO phase of PCMO and the corresponding spin memory effect is a direct consequence of hysteretic first-order phase transition arising from the weakening of the CO state under the external magnetic field and trapping of the spins due to a strong pinning potential in the material.     

Modulation of magnetic properties and enhanced magnetoelectric effects in MnW_(1-x)Mo_xO_4 compounds

In this letter, we investigate the magnetic and ferroelectric properties of polycrystalline MnW1-xMoxO4 （x = 0, 0.05, 0.10, 0.20） compounds. The substitution of nonmagnetic Mo6＋ ions for W6＋ ions modifies the magnetic transition tem- peratures of MnW1-xMoxO4 by changing the Mn-O-Mn bond. As a result, distinct ferroelectric properties and enhanced magnetoelectric effects are observed in Mo6＋-doped MnWO4 compounds. The effects of substitution of Mo6＋ ions on magnetic properties and magnetoelectric coupling are discussed.     

Magnetic entropy change and magnetic properties of LaFe_(11.5)Si_(1.5) after controlling the Curie temperature by partial substitution of Mn and hydrogenation

Magnetic properties and magnetic entropy changes of La(Fe_(1-x)Mn_x)_(11.5)Si_(1.5)H_y compounds are investigated. Their Curie temperatures are adjusted to room temperature by partial Mn substitution for Fe and hydrogen absorption in 1-atm(1 atm = 1.01325×10~5Pa) hydrogen gas. Under a field change from 0 T to 2 T, the maximum magnetic entropy change for La(Fe_(0.99)Mn_(0.01))_(11.5)Si_(1.5)H_(1.61)is-11.5 J/kg. The suitable Curie temperature and large value of ?S_m make it an attractive potential candidate for the room temperature magnetic refrigeration application.     

Structural,electronic, and optical properties of ZnO_(1-x)Se_x alloys using first-principles calculations

The structural, electronic, and optical properties of binary ZnO, ZnSe compounds, and their ternary ZnO 1-x Se x alloys are computed using the accurate full potential linearized augmented plane wave plus local orbital (FP-LAPW + lo) method in the rocksalt (B1) and zincblende (B3) crystallographic phases. The electronic band structures, fundamental energy band gaps, and densities of states for ZnO 1-x Se x are evaluated in the range 0 ≤ x ≤ 1 using Wu-Cohen (WC) generalized gradient approximation (GGA) for the exchange-correlation potential. Our calculated results of lattice parameters and bulk modulus reveal a nonlinear variation for pseudo-binary and their ternary alloys in both phases and show a considerable deviation from Vegard's law. It is observed that the predicted lattice parameter and bulk modulus are in good agreement with the available experimental and theoretical data. We establish that the composition dependence of band gap is semi-metallic in B1 phase, while a direct band gap is observed in B3 phase. The calculated density of states is described by taking into account the contribution of Zn 3d, O2p, and Se 4s, and the optical properties are studied in terms of dielectric functions, refractive index, reflectivity, and energy loss function for the B3 phase and are compared with the available experimental data.