Coexistence of localized magnetism and itinerant ferromagnetism in a Gd5Y2Pd3 single crystal

Experimental results of the single-crystal X-ray diffraction, XPS, ac-magnetic susceptibility (ac-χ), dc-magnetization M(T), and electrical resistivity (ρ) measurements for the hexagonal Th₇Fe₃-type Gd₅Y₂Pd₃ single crystal are presented. Anomalies in (ac-χ), (T) and M(T)-curves have allowed to establish that Gd₅Y₂Pd₃ undergoes a long-range ferromagnetic-type ordering at T_C = 263 K, followed by a spin-reorientation below 190 K. The magnetization data indicate that there is an excess of the magnetic moment for the Gd³⁺ ions. The observed XPS, magnetic and electrical resistivity behaviour points to the coexistence of localized magnetism from the magnetic Gd³⁺ ions and itinerant ferromagnetism from 4d- and 5d-electron bands. We discuss the magnetic behaviour of the Gd_7−xY_xPd₃ solid solutions in terms of three competitive mechanisms: RKKY-interaction, magnetic frustration and spin-fluctuation.     

Elastic constants of amorphous and single-crystal Pd40Cu40P20

We have measured the adiabatic second-order elastic constants of amorphous Pd₄₀Cu₄₀P₂₀ (isotropic, two independent elastic constants) and single-crystal Pd₄₀Cu₄₀P₂₀ (tetragonal, six independent elastic constants) over the range 3.9 < T < 300 K. Below ∼20 K, the elastic constants of single-crystal Pd₄₀Cu₄₀P₂₀ vary as C(T) = C(0)[1 − bT² − dT⁴], which is the same temperature dependence found in metallic elements. In contrast, below ∼20 K the elastic constants of amorphous Pd₄₀Cu₄₀P₂₀ vary as C(T) = C(0¹)[1 − aT]. The bulk modulus of amorphous Pd₄₀Cu₄₀P₂₀ is approximately 2% lower than that of crystalline Pd₄₀Cu₄₀P₂₀, whereas the shear modulus of the glass is 13–36% lower than the four independent shear moduli of the tetragonal crystal. The lower moduli of the glass are best explained by additional atomic displacements, beyond those experienced by the atoms in a crystal, that occur because the atoms in glasses do not occupy centers of symmetry.     

The magnetocaloric properties of GdScSi and GdScGe

The magnetocaloric properties of the ferromagnetic compounds GdScSi (T_C = 354(2) K) and GdScGe (T_C = 349(2) K) (tetragonal CeScSi-type structure refined from single crystal diffractometer data, space group I4/mmm) have been determined. The field dependence of the magnetic entropy ΔS_m change and of the refrigerant capacity RC have been obtained from magnetization measurements. At the T_C Curie temperature, ΔS_m for GdScSi and GdScGe is respectively equal to 2.5 and 3.3 J/kg_Gd K for a magnetic field change of 2 T; the values are comparable to those determined previously for Gd₇Pd₃ and Gd₄Bi₃ which exhibit also a T_C-temperature higher than room temperature. Both microstructural and the analysis of the magnetocaloric response are used to assess the single phase nature of the samples.     

Magnetocaloric properties of a novel ferromagnet Gd3Co4+xAl12−x (x = 0.50)

A novel gadolinium and cobalt based aluminide, namely Gd₃Co_4+xAl_12−x (x = 0.50(3)) is shown to crystallize in the hexagonal Gd₃Ru₄Al₁₂ structure-type (space-group P6₃/mmc, a = 8.6830(1) Å, c = 9.3164(2) Å at room temperature). The investigation of its magnetic properties revealed a reversible ferromagnetic ordering at T_C ≈ 40 K but expanding in a wide temperature range, potentially due to the geometrical magnetic frustrations expected in this structure-type. The magnetocaloric properties of this intermetallic, determined from both magnetization and specific heat data, are dominated by a maximum entropy variation of −3.28 J kg⁻¹ K⁻¹ at 39(1) K and an adiabatic temperature change of about 1.5 K extending from 20 to 40 K, highlighting some interest for low temperature applications.     

Hydrogenation properties of shape memory Ti(Ni,Pd) compounds

The effect of Pd substitution on the crystal structure and hydrogenation properties of TiNi compound has been investigated. Ti(Ni,Pd) are pseudo-binary compounds. The unit-cell volumes of B2 (Austenite) and B19 (Martensite) structures linearly increase with Pd substitution in Ti_1.04Ni_0.96?xPd_x samples. The hydrogenation properties of Pd-substituting Ti(Ni,Pd) compounds are not affected by the crystal structure of the parent compounds. For all samples, hydrogen absorption occurs without showing any clear plateau pressure in Pressure-Composition-Isotherm (PCI) curves. All hydrided samples crystallise in the tetragonal I 4/mmm space group. At 6 MPa of hydrogen pressure and T = 423 K, the hydrogenation capacity of Ti(Ni,Pd) compounds reaches 1.52 hydrogen atoms per formula unit (H/f.u.) for x = 0.1 and then gradually decreases with Pd content down to 0.93 H/f.u. for x = 0.5. Ti_1.04Ni_0.86Pd_0.10 sample yields a discharge capacity of 148 mAh/g at C/5 regime when used as negative electrode in Ni-MH battery. The hydrogenation properties of Pd-substituting Ti(Ni,Pd) compounds are discussed in detail by comparison with previous studies on Zr substituting, (Ti,Zr)Ni compounds.     

Magnetic properties and magnetocaloric effect of FeCrNbYB metallic glasses with high glass-forming ability

The influences of Cr addition on the Curie temperature (T_C), glass-forming ability (GFA), and magnetocaloric effect were investigated in FeCrNbYB metallic glasses. It was found that the addition of Cr element slightly decreases the GFA and saturation magnetization, whereas effectively modulates T_C. By the method of copper mold casting, bulk metallic glasses (BMGs) with critical diameters up to 5 mm can be obtained in Fe_68−xCr_xNb₄Y₆B₂₂ (x = 2–6) alloys. The resulting metallic glasses exhibit T_C of 271–367 K and excellent magnetocaloric properties, including magnetic entropy change of 0.76–1.05 J/kg K, and refrigerant capacity of 83–93 J/kg under a low field change of 1.5 T. In addition, they exhibit a wide supercooled liquid region of 116–135 K. The successful synthesis of the FeCrNbYB BMGs with near room-temperature magnetocaloric properties is encouraging for the future development of Fe-based BMGs as a new magnetic refrigerant in magnetic cooling system.     

New ternary Yb5Sb3-type R5T1−x{Sb,Bi}2+x phases (R = Y,Dy, Ho,T = Co,Ru, Rh,Pd) and their magnetic properties

Several novel R₅T_1?x{Sb,Bi}_2+x phases having the Yb₅Sb₃-type structure (space group Pnma) have been synthesized. The cell parameters are: a = 1.20668(9), b = 0.88396(7), c = 0.78745(7) nm for Y₅CoSb₂; a = 1.19939(7), b = 0.88364(5), c = 0.78283(5) nm for Dy₅CoSb₂; a = 1.19633(8), b = 0.89231(6), c = 0.78450(6) nm for Ho₅RhSb₂; a = 1.18650(6), b = 0.90455(4), c = 0.79260(4) nm for Ho₅PdSb₂; a = 1.2215(3), b = 0.8948(2), c = 0.7977(2) nm for Y₅CoBi₂; a = 1.1781(8), b = 0.9071(7), c = 0.7936(6) nm for Tm₅Co_0.5Bi_2.5; a = 1.1972(1), b = 0.92096(9), c = 0.80048(9) nm for Ho₅RuBi₂; a = 1.2082(1), b = 0.90346(9), c = 0.79413(8) nm for Ho₅RhBi₂ and a = 1.20374(5), b = 0.91076(4), c = 0.80135(4) nm for Ho₅PdBi₂, respectively. Magnetization measurements indicate ferromagnetic transitions for Dy₅CoBi₂, Ho₅RhSb₂, Ho₅RhBi₂, Ho₅PdSb₂ and Ho₅PdBi₂ at T_C = 34, 38, 28, 42 and 38 K, respectively. The Ho₅RhSb₂ and Ho₅PdBi₂ compounds show additional magnetic transitions at about 18 K, probably associated with a spin reorientation. The magnetocaloric effect of Dy₅CoBi₂ in terms of the isothermal entropy change, ΔS_m, is ?6.2 J/(kg/K) at 38 K and in terms of the adiabatic temperature change, ΔT_ad, is 2.2 K for a 5 T field change.     

Magnetocaloric effect over a wide temperature range in GdxHo3−xAl2 compounds with successive magnetic transitions

The Gd_xHo_3−xAl₂ (x = 0.5–2.5) compounds undergo two successive magnetic transitions: a second-order magnetic transition from paramagnetism (PM) to ferromagnetism (FM) around T_C followed by a FM to ferrimagnetism (FIM)-like transition at T_t. The T_C increases linearly with the increase of Gd content due to the de Gennes factor of Gd being larger than that of Ho, while the T_t remains nearly constant around 45 K independent of the variation of Gd content. The working temperature range is expanded by substituting Ho with Gd atoms due to the higher transition temperature of Gd₃Al₂ and the different composition dependence of successive magnetic transitions, and thus leading to an enhanced refrigerant capacity (RC). For a relatively low field change of 2 T, a giant RC value of 272 J/kg with a wide working temperature range of ∼80 K is obtained for x = 1.0 compound due to the partial overlap of successive ΔS_M peaks. This is probably the largest RC value so far reported in the temperature range of liquid natural gas (111 K). Consequently, the large ΔS_M and giant RC suggest that Gd_xHo_3−xAl₂ compounds could be good candidates of magnetic refrigerants in a wide temperature range.     

Effects of Co substitution for Fe on the glass forming ability and properties of Fe80P13C7 bulk metallic glasses

Bulk magnetic Fe_80−xCo_xP₁₃C₇ (x = 0, 5, 10, 15, 20 at.%) glassy alloy rods were prepared by the combination method of fluxing treatment and J-quenching technique, and the attainable maximum diameter for fully glass formation gets to 2.5 mm for x = 5. The effects of Co substitution for Fe on the glass formation ability (GFA), thermal stability, mechanical properties and magnetic properties have been investigated systematically. It was found that the partially substitution of Co for Fe can enhance the GFA of Fe₈₀P₁₃C₇ alloy, while excessive substitution will lead to the degradation of GFA. The compressive test shows that the substitution of Co for Fe results in the decease of fracture strength, and then significantly enhance the room temperature plastic strain of the present Fe-based BMGs, which can be identified that the plastic strain at room temperature gets to 2.5% and 3.0% for x = 5 and 10, respectively. The saturation magnetization of Fe_80−xCo_xP₁₃C₇ (x = 0, 5, 10, 15, 20 at.%) BMGs firstly increases from 1.477 T to 1.550 T with increasing Co content from x = 0 to 5, and then deceases from 1.549 T to 1.519 T with increasing Co content from x = 5 to 20. The Curie temperature of the present FeCoPC BMGs quickly increases with the substitution of Co for Fe.     

Thermoelectric properties of Fe0.2Co3.8Sb12−xTex skutterudites

Skutterudites Fe_0.2Co_3.8Sb_12?xTe_x (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) were synthesized by induction melting at 1273 K, followed by annealing at 923 K for 144 h. X-ray powder diffraction and electron microprobe analysis confirmed the presence of the skutterudite phase as the main phase. The temperature-dependent transport properties were measured for all the samples from 300 to 818 K. A positive Seebeck coefficient (holes are majority carriers) was obtained in Fe_0.2Co_3.8Sb₁₂ in the whole temperature range. Thermally excited carriers changed from n-type to p-type in Fe_0.2Co_3.8Sb_11.9Te_0.1 at 570 K, while in all the other samples, Fe_0.2Co_3.8Sb_12?xTe_x (x = 0.2, 0.3, 0.4, 0.5, 0.6) exhibited negative Seebeck coefficients in the entire temperature range measured. Whereas for the alloys up to x = 0.2 (Fe_0.2Co_3.8Sb_11.8Te_0.2) the electrical resistivity decreased by charge compensation, it increased for x > 0.2 with an increase in Te content as a result of an increase in the electron concentration. The thermal conductivity decreased with Te substitution owing to carrier–phonon scattering and point defect scattering. The maximum dimensionless thermoelectric figure of merit, ZT = 1.04 at 818 K, was obtained with an optimized Te content for Fe_0.2Co_3.8Sb_11.5Te_0.5 and a carrier concentration of ～n = 3.0 × 10²⁰ cm^?3 at room temperature. Thermal expansion (α = 8.8 × 10^?6 K^?1), as measured for Fe_0.2Co_3.8Sb_11.5Te_0.5, compared well with that of undoped Co₄Sb₁₂. A further increase in the thermoelectric figure of merit up to ZT = 1.3 at 820 K was achieved for Fe_0.2Co_3.8Sb_11.5Te_0.5, applying severe plastic deformation in terms of a high-pressure torsion process.     

Magnetic properties and tuneable magnetocaloric effect with large temperature span in GdCd1−xRux solid solutions

The magnetic properties and the magnetocaloric effect (MCE) in the GdCd_1−xRu_x (x = 0.1, 0.15, and 0.2) solid solutions have been systematically investigated. A large reversible MCE has been observed in GdCd_1−xRu_x accompanied by a second order magnetic phase transition from paramagnetic to ferromagnetic at T_C ∼ 149, 108, and 73 K for x = 0.1, 0.15, and 0.2, respectively. Under a field change from 0 to 7 T, the maximum values of magnetic entropy change (–ΔS_M^max) are 5.6, 7.8, and 11.0 J/kg K for x = 0.1, 0.15, and 0.2, respectively, the corresponding values of the relative cooling power (RCP) are 889, 852, and 828 J/kg. The considerable reversible MCE and large RCP values together with the tuneable T_M in a wide temperature range make the GdCd_1−xRu_x solid solutions considerable for active magnetic-refrigeration.     

Crystal structure and properties of U2Co3Al9

A new ternary compound with stoichiometry U₂Co₃Al₉ has been synthesized. It adopts the orthorhombic Y₂Co₃Ga₉-type structure (space group Cmcm, Z = 4, a = 12.824(2) Å, b = 7.515(1) Å, c = 9.249(2) Å). Measurements of dc- and ac-magnetic susceptibility, electrical resistivity, and magnetoresistivity on polycrystalline samples have been performed. The Curie–Weiss law is strictly followed, with θ_CW = −48 K and μ_eff = 3.2 μ_B. A small kink observed in the temperature dependence of the resistivity is attributed to a phase transition at T_t = 8 K. The magnetoresistivity was found to be negative at all temperatures examined below 45 K, with a sharp minimum at T_t = 8 K.     

Structural,magnetic and magnetoelastic properties of Laves-phase Tb0.3Dy0.6Nd0.1(Fe1-xCox)1.93 compounds (0 ≤ x ≤ 0.40)

Structure, magnetization and magnetostriction of Tb_0.3Dy_0.6Nd_0.1(Fe_1-xCo_x)_1.93 (0 ≤ x ≤ 0.40) compounds have been investigated. X-ray diffraction (XRD) analysis shows the presence of single Laves phase with a cubic MgCu₂-type structure. The easy magnetization direction (EMD) is observed to be <111> direction when x ≤ 0.10, and deviates away with further increasing Co contents. The Co contributes an opposite role in the resultant magnetocrystalline-anisotropy compared to Tb. A small amount of Co substitution for Fe can enhance the Curie temperature for x ≤ 0.25. The magnetocrystalline-anisotropy compensation can be achieved in this system. A minimum in anisotropy is obtained for the Tb_0.3Dy_0.6Nd_0.1(Fe_0.8Co_0.2)_1.93 compound, which has good magneto-elastic properties, e.g., the large saturation magnetostriction λ_S (∼930 ppm) and the high low-field magnetostriction λ_a (∼670 ppm/3 kOe), and may make it technological interest in the field of magnetostrictive materials.     

First-principles phase stability calculations and estimation of finite temperature effects on pseudo-binary Mg6(PdxNi1−x) compounds

The stability of pseudo-binary Mg₆(Pd_xNi_1?x) compounds has been studied at T = 0 K via first-principles calculations and at 673 K by thermodynamic modelling of finite temperature effects. At 0 K, these compounds are not stable since their formation energy is above the convex hull defined by the Mg, Mg₂Ni and Mg₆Pd phases, although the energy difference is not very high. However, at 673 K, vibrational and configurational entropic effects allow the stabilisation of some of the calculated pseudo-binary Mg₆(Pd_xNi_1?x) compounds. The vibrational contribution to the thermodynamic properties of the studied compounds has been calculated from Debye temperatures in the harmonic approximation. Also, the configurational entropy has been estimated taking into account the possible distribution of Pd and Ni between the several sites available in the pseudo-binary structure. The identification of intrinsic disorder and the associated energies and entropy are innovative features of this work. The phase diagram at the Mg-rich corner derived from these calculations is in fairly good agreement with recently published experimental results. In addition, the Ni for Pd substitution has been studied for the several sites available for Pd in the binary Mg₆Pd compound. The calculated preferential site occupancy is in agreement with the site occupancy factors determined in recent neutron diffraction experiments.     

Preparation and properties of quaternary CoMoPB bulk metallic glasses

A new series of Co_80−xMo_xP₁₄B₆ (x = 7, 9, and 11 at%) bulk glassy alloys were successfully prepared by a combination method of fluxing treatment and J-quenching technique. The glass-forming ability (GFA) of the obtained Co-based alloys is sensitive to the Mo content substituted for Co, and the maximum attainable diameter for a fully amorphous state can reach 4.5 mm at x = 9. The compressive tests show that the obtained Co-based BMGs exhibit a compressive strength of 3.3–3.9 GPa, but nearly zero compressive plasticity. The new Co-based BMGs possess good soft magnetic properties, and their saturated magnetization values decrease from 47 emu/g (0.45 T) to 14 emu/g (0.14 T) with increasing the content of the Co substitute from 7 at% to 11 at%, which may be attributed to the anti-ferromagnetic coupling between the Mo and Co atoms. Because of their good GFA, high Co content, few constituting elements, and relatively high strength, the obtained Co-based BMGs (especially Co₇₁Mo₉P₁₄B₆ BMG) can be considered promising as starting alloys to develop the new Co-based BMGs for the advanced structural and functional applications.     

Magnetic and transport properties of Laves phase Dy1−xMmxCo2 (x = 0–0.5) alloys

The influence of Mm substitution (Mm = mischmetal) on structural, transport and magnetic properties of (Dy_1?xMm_x)Co₂ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) alloys has been investigated by means of X-ray diffraction (XRD), temperature dependent electrical resistivity (ρ(T)), ac susceptibility (χ(T)) and thermopower (S(T)). XRD patterns show the formation of solid solutions crystallizing with cubic Laves (C15) type structure at room temperature. The pronounced discontinuities in the resistivity and thermopower at Curie temperature (T_C) are explained based on the suppression of the spin-fluctuation contribution. The gradual decrease in T_C and sharpness of discontinuities in ρ(T) and S(T) with increasing Mm substitution has been discussed.     

Magnetic and transport properties in the Heusler series Ni2−xMn1+xSn affected by chemical disorder

Crystal structure, magnetic and transport characteristics of Ni_2−x Mn_1+x Sn Heusler series have been studied with the emphasis on chemical disorder effects. It is shown that the structure and the disorder character in these series can be predicted by using simple rules. Ni₂ MnSn is a ferromagnetic, congruent melting phase, which crystallizes cubic in the L2₁ structure type. By increasing x, Ni and Mn atoms randomly mix and occupy the heterocubic sites of the regular Heusler structure, and the magnetic structure becomes ferrimagnetic. The total magnetic moment m_sat decreases linearly in the range 0.2 ≤ x ≤ 1, while the Curie temperature T_C increases. At low Mn content (x < 0.2), the unit cell volume shows anomalous behavior, characterized by constant m_sat and T_C. Electrical resistivity, Seebeck coefficient, and thermal conductivity strongly depend on the amount of disorder, which increases with the Mn content. Results of first-principle calculations based on the coherent potential approximation (CPA) alloy theory for the magnetic and electrical properties are in reasonable agreement with the simple rules and all experimental data.     

Fe-Co-Ni-Cr-Mo-C-B-Y系大块金属玻璃的热稳定性、晶化行为、维氏硬度和磁性能

研究Fe41Co7-xNixCr15Mo14C15B6Y2(x=0,1,3,5)大块金属玻璃的热稳定性、晶化行为、维氏硬度和磁性能.通过铜模铸造法制备Fe41Co7-xNixCr15Mo14C15B6Y2(x=0,1,3,5)大块金属玻璃.利用差示扫描量热法和等温热处理法研究这些金属玻璃的热稳定性和晶化行为.在室温下利用维氏硬度计测量试样经过不同温度和时间退火后的硬度,并对它们的磁学性质进行表征.实验结果表明,少量Ni元素的加入没有增大过冷液相区间和玻璃形成能力,但是改变合金的初始晶化行为,增大晶化激活能.少量Ni元素的加入能够细化最终晶化组织中的晶粒大小.初晶相使合金的硬度降低,但随着热处理温度的升高,所有合金的硬度都明显提高,原因是析出了大量的碳化物和硼化物.退火温度对合金的磁性能有很大影响,少量Ni元素的加入阻止了合金在高温退火后从顺磁态向铁磁态的转变.     

Investigation of the dependency of the upper critical magnetic field on the content x in Y1−xYbx/2Gdx/2Ba2Cu3O7−y superconducting structures

The Y_1−xYb_x/2Gd_x/2Ba₂Cu₃O_7−y superconducting samples for x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared by using the solid-state reaction technique. Resistivity measurements of the samples were performed in QD–PPMS system under different magnetic fields up to 5 T in zero fields cooling regime. Using the resistivity data, the upper critical magnetic field H_c2(0) at T = 0 K for 50% of R_n was calculated by the extrapolation H_c2(T) to the temperature T = 0 K. The coherence length in T = 0 K were calculated from H_c2(0) and the effects of x in the composition on both the coherence length and the upper critical magnetic field were examined. The results showed that H_c2(0) varied from 84.05 to 122.26 T with the content x. The upper critical magnetic field in the temperature T = 0 K slightly decreased with increasing the content x. Using the content x, the upper critical magnetic field can be controlled and this can be used in the superconductivity applications.     

Enthalpies of formation of selected Pd2YZ Heusler compounds

Standard enthalpies of formation of selected ternary Pd-based Heusler type compositions Pd₂YZ (Y = Cu, Hf, Mn, Ti, Zr; Z = Al, Ga, In, Ge, Sn) were measured using high temperature direct synthesis calorimetry. The measured enthalpies of formation (in kJ/mole of atoms) of the Heusler compounds are, Pd₂HfAl (−81.6 ± 2.4); Pd₂HfGa (−79.9 ± 2.9); Pd₂HfIn (−76.4 ± 1.4); Pd₂HfSn (−77.6 ± 1.6); Pd₂MnSn (−54.6 ± 3.1); Pd₂TiGa (−65.6 ± 3.6); Pd₂TiIn (−69.9 ± 2.1); Pd₂TiSn (−78.6 ± 2.4); Pd₂ZrAl (−85.3 ± 3.0); Pd₂ZrGa (−76.2 ± 1.9); Pd₂ZrIn (−85.1 ± 3.9); Pd₂ZrSn (−92.2 ± 3.1); for the B2 compounds, Pd₂MnAl (−87.1 ± 3.0); Pd₂MnGa (−54.5 ± 1.7); Pd₂MnIn (−41.0 ± 2.5); Pd₂TiAl (−81.4 ± 1.9); for the tetragonal compound Pd₂CuAl (−55.2 ± 3.0) and for the orthorhombic compound Pd₂CuSn (−43.1 ± 2.3). Values were compared with those from published first principles calculation and the Open Quantum Materials Database (OQMD). Lattice parameters of these compounds were determined by X-ray diffraction analysis (XRD). Microstructures were identified using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Selected alloys were annealed at various temperatures to investigate phase transformations and phase relationships.