Pressure effect on curie temperature in (CoTm)90Zr10 (Tm = Cr,Mo) amorphous alloys

The forced volume magnetostriction in (CoTm)₉₀Zr₁₀ (Tm = Cr, Mo) amorphous alloys was measured by the 3-terminal capacitance method in the fields up to 18 kOe and in the temperature range of 77 K to the Curie temperature or crystallization temperature. From the temperature dependence of the forced volume magnetostriction, the pressure effects on magnetization and Curie temperature are estimated indirectly using the thermodynamical relation between the forced volume magnetostriction and the pressure effect on magnetization. The results obtained indirectly indicate that the pressure effect on Curie temperature approaches nearly zero in Co₉₀Zr₁₀ amorphous alloy, though it cannot be measured directly under pressure.     

The Hall effect in amorphous (Zr0.64Ni0.36)1−x M x alloys (M=Al,Ga)

Values of the room temperature Hall coefficients and electrical resistivity of amorphous melt spun (Zr_0.64Ni_0.36)_1–x Al _x and (Zr_0.64Ni_0.36)_1–x Ga _x alloys forx=0–0.25 are reported. Addition of Al or Ga to Zr_0.64Ni_0.36 dramatically increases the already positive Hall coefficient of this alloy and also increases the electrical resistivity and crystallization temperature.     

Formation of Fe-Nb-X (X=Zr, Ti) amorphous alloys from pure metal elements by mechanical alloying

Fe-based amorphous powders of Fe₅₆Nb₆Zr₃₈ and Fe₆₀Nb₆Ti₃₄ based on binary eutectic were prepared by mechanical alloying starting from mixtures of pure metal powders. The amorphization behavior and thermal stability were examined by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and differential scanning calorimetry. Results show that Fe₅₆Nb₆Zr₃₈ alloy has a better glass forming ability and a relatively lower thermal stability comparing with Fe₆₀Nb₆Ti₃₄ alloy. The prepared amorphous powders have homogeneous element distribution and no obvious contaminants coming from mechanical alloying. The synthesized amorphous powders offer the potential for consolidation to full density with desirable mechanical properties through the powder metallurgy methods.     

Structural relaxation,crystallization and improvement of magnetic properties in FeXSiB (X=Cr,Nb)-type amorphous alloys

In the present paper, the influence of Nb and Cr on intensity of structural relaxation, crystallization processes, electric and magnetic properties in the Fe₇₆Nb₂Si₁₃B₉, Fe₇₆Cr₂Si₁₃B₉ and Fe₇₆Nb₁Cr₁Si₁₃B₉ alloys were investigated. It was shown that the improvement of magnetic permeability caused by a suitable annealing is a thermally activated process. Activation energy of this process is found to be of the order of 1 eV. Cr as an alloying addition to the Fe–Si–B alloy does not change the 1 h optimization annealing temperature and causes an increase of its efficiency. Nb as an alloying addition causes an increase of the 1 h optimization annealing temperature, and also the temperature of the first step of crystallization.     

Spin glass behavior in the new amorphous alloys M2SnTe4 (M=Cr,Mn, Fe)

The amorphous alloys M₂SnTe₄ (M=Cr, Mn, Fe) are prepared by a new method involving the oxidation of main group polyanions (Zintl anions) by transition metal cations in solution at or below room temperature. The M₂SnTe₄ materials undergo a transition to a spin glass state at 12 K ? T_f ? 20 K and were characterized by dc magnetization, ⁵⁷Fe and ¹¹⁹Sn Mossbauer and x-ray diffraction measurements as well as the behavior of the remanent magnetization.     

Magnetic properties and magnetocaloric effect in RE55Co30Al10Si5 (RE = Er and Tm) amorphous ribbons

The magnetic and magnetocaloric effects (MCE) of the amorphous $RE_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ ($RE={\rm Er}$ and Tm) ribbons were systematically investigated in this paper. Compounds with $R ={\rm Er}$ and Tm undergo a second-order magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) around Curie temperature $T_{\rm C} \sim 9.3$ K and 3 K, respectively. For Er$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ compound, an obvious magnetic hysteresis and thermal hysteresis were observed at low field below 6 K, possibly due to spin-glass behavior. Under the field change of 0 T-5 T, the maximum values of magnetic entropy change ($-\Delta S_{\rm M}^{\rm max}$) reach as high as 15.6 J/kg$\cdot$K and 15.7 J/kg$\cdot$K for Er$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ and Tm$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ compounds, corresponding refrigerant capacity (RC) values are estimated as 303 J/kg and 189 J/kg, respectively. The large MCE makes amorphous $RE_{55}$Co$_{30}$Al$_{10}$Si$_{5 }$ ($RE={\rm Er}$ and Tm) alloys become very attractive magnetic refrigeration materials in the low-temperature region.     

The effect of internal stresses on the magnetization curve of amorphous ferromagnetic FeNi alloys

The Rayleigh region, the coercive field and the magnetization curves of the amorphous, ferromagnetic alloys Fe_80−xNi_xB₂₀ and Fe₄₀Ni₄₀P₁₄B₆ have been investigated as a function of the temperature and composition. It is shown that the characteristic parameters of the magnetization curves can be described by the statistical potential theory as developed previously for the movement of domain walls. Our experimental results are compatible with the assumption that the obstacles opposing the domain wall displacements are elastic stress centres produced during the rapid quenching process of the amorphous alloys.     

Mössbauer study on surface crystallization behavior of amorphous Fe90Zr10 alloy ribbon

The precipitous drop of crystallization temperature at the surface of amorphous Fe₉₀Zr₁₀ ribbon is confirmed by TMS and CEMS. The deficiency in Zr at the surface amorphous phase, caused by the absorption and the diffusion of oxygen, is found to be responsible for it. The final crystalline products are assigned to α-Fe, Fe₃Zr and Fe₂Zr, whereas only α-Fe precipitates at the surfaces. Moreover, it is indicated that the crystallization behavior of the bulk is influenced by the ambient gases during annealing and quite different between in vacuum and in air.     

Metallic magnetism in amorphous TM-Y (TM = Mn,Fe, Co,Ni) alloys

Systematic variations of magnetic properties in amorphous TM-Y (TM = Mn, Fe, Co, Ni) alloys are investigated on the basis of a finite temperature theory of amorphous metallic magnetism which takes into account both thermal spin fluctuations and the fluctuations due to structural and configurations disorder. It is shown that the magnetic phase diagrams calculated in the most random atomic configuration explain qualitatively the spinglass (SG) in Mn-Y, the SG ferromagnetism (F) transition in Fe-Y, and the F-paramagnetism transition in Co-Y and Ni-Y alloys. Magnetization vs concentration curves and susceptibility vs concentration curves as well as the effective Bohr magneton numbers are also shown to be explained qualitatively or semi-quantitatively by the theory. Their miscroscopic mechanisms are elucidated by means of their electronic structures, magnetic couplings, and atomic short range order. It is found that the magnetism in Fe-Y and Mn-Y amorphous alloys is strongly influenced by the atomic short range order. The result explains different magnetic phase diagrams in amorphous Fe-Y alloys and experimental SG transition temperatures in amorphous Mn-Y alloys.     

Outstanding magnetocaloric effect of Fe_(88-x)Zr_8B_4Sm_x(x=0, 1, 2, 3) amorphous alloys

正Since the first investigation on the formation and magnetic properties of Fe-C-P amorphous phase by Duwez and Lin in1967[1,2],Fe-based amorphous alloys have attracted extensive interest because of their low cost,excellent soft magnetic properties,good corrosion resistance,and mechanical properties[2-7].Among the Fe-based amorphous alloys,Fe-Zr-B ternary amorphous alloys exhibit excellent magnetocaloric effect(MCE)near room temperature,and thus,act as a fertile ground for the exploration of novel working materials for magnetic refrigerators[6-14].     

Electronic structure of amorphous Zr based alloys with V,Cr and Mn studied by photoelectron spectroscopy and bandstructure calculations

The electronic structure of the amorphous alloys V₃₆Zr₆₄, Cr₃₀Zr₇₀ and Mn₃₀Zr₇₀ has been studied by photoelectron spectroscopy (UPS, XPS) and bandstructure calculations for the ordered analogs. The valence band photoelectron spectra and the calculated density of states reveal a large contribution to the state density at the Fermi level from the 3d metal. This behavior is characteristic of Zr based alloys with early 3d transition metals and differs from alloys with higher 3d electron numbers in which the 3d band is located at higher energies. The implications of the high density of states at E_F of the amorphous Zr-(V, Cr, Mn) alloys for magnetism and the occurrence of superconductivity is discussed.     

Anomalous magnetic behavior of Ce1−xMxCo5(M=Zr,Hf) alloys

The compound CeCo₅ is ferromagnetically ordered with a Curie temperature (T_c) of 641 K and a moment (μ_Co) of 1.36μ_B per Co atom at 77 K. Replacement of Ce by Hf or Zr in CeCo₅ reduces the magnetic moment on cobalt but substantially increases the Curie temperature. For instance, in Ce_0.8Hf_0.2Co₅μ_Co=1.12μ_B at 77 K and T_c=846 K. These results indicate a much stronger d-d electron interaction in the ternary alloys than in CeCo₅. Ce in these systems behaves as if it is nearly quadrivalent.     

Magnetic hyperfine fields in Heusler alloys Co YZ (Y=Ti,Zr; Z=Al,Ga,Sn)

Magnetic hyperfine fields (mhf) acting on Ta at the Ti and Zr sites have been measured in Heusler alloys Co₂TiAl(Ga,Sn) and Co₂ZrAl(Sn) by the TDPAC technique utilizing the 133–482 keV gamma cascade in¹⁸¹Hf. Curie temperatures of all the alloys have also been measured using a vibrating sample magnetometer. Present data together with the existing results on the Co₂HfAl(Ga,Sn) are discussed and compared with the mhf systematics in Heusler alloys.work partially supported by CNEN and CNPq     

Solid-phase reactions between (100) GaAs and thin-film refractory metals (Ti,Zr, V,Nb, Cr,Mo, and W)

Recently, there has been an increased interest in the applications of refractory metals as gate materials for the self aligned gate process in the fabrications of GaAs field effect transistors. In this study, we systematically investigated the thermally induced interface interactions between (100) GaAs substrates and thin films of refractory metals (Ti, Zr, V, Nb, Cr, Mo, and W). Depth profilings of the M/GaAs interfaces were obtained using conventional and heavy ion Rutherford backscattering spectrometry. Phase identifications were achieved by x-ray diffraction.Results on the phase formation sequence, reaction kinetics, the distribution, composition and structure of the reacted phases and the interface reactivity of these contacts will be presented. Correlations between metal properties (electronegativity and metal-metal bond strength) and kinetics of the reactions (activation energy and reactivity of the interfaces) will also be discussed.     

Mössbauer study of amorphous Fe2RE (RE=Ce,Er) alloys

Among amorphous Fe₂RE (RE=Er, Ce, Gd, La, Pr, Sm, Dy, Ho) alloys, Fe₂Ce exhibits a tendency toward short range order, while the other Fe₂RE compounds show clustering. However, we have almost no information about environments around Fe atoms. Using Mössbauer spectroscopy we have determined the quadrupole splitting distributionsP(QS) of two representative amorphous Fe₂RE (RE=Ce, Er) alloys, leading to local environments of Fe atoms. The analysis of the mixed magnetic dipole and quadrupole interactions in Fe₂Er shows two kinds of electrical field gradients (EFT) with the positive and negative signs in the sample, indicating a random packing of Fe atoms. Furthermore, the analyzed quadrupole splitting distributionP(QS) of Fe₂Er also supports random packing in this amorphous alloy. On the other hand, the amorphous Fe₂Ce alloy shows two kinds of distributions of quadrupole splitting; the major component indicating random packing and the minor component Ce-rich Ce-Fe clusters.     

Terahertz time-domain spectroscopy and optical properties of AM2O8 (A=Zr,Hf and M=W,Mo)

Terahertz time domain spectroscopy and optical properties of cubic ZrW₂O₈ and HfW₂O₈, and trigonal ZrMo₂O₈ and HfMo₂O₈ have been studied for the first time. It is shown that α-ZrW₂O₈ and α-HfW₂O₈ exhibit absorption peaks around 1.23 THz (41 cm^?1) and 1.18 THz (39.5 cm^?1), respectively, whereas no corresponding absorptions are observed for trigonal ZrMo₂O₈ and HfMo₂O₈. These external modes are suggested to originate from the librational and/or translational motions of the linked ZrO₆/HfO₆ and WO₄ polyhedra and to contribute to the negative thermal expansion of α-ZrW₂O₈ and α-HfW₂O₈. The absorption coefficients and refractive indices of these materials are derived from the transmission amplitudes of the THz field passing through the samples. The results suggest that cubic ZrW₂O₈ and HfW₂O₈ have the potential for THz filters or attenuators.     

Anisotropic elastic properties of MB (M = Cr,Mo, W) monoborides: a first-principles investigation

First principles calculations were performed to systematically investigate structure properties, phase stability and mechanical properties of MB (M = Cr, Mo, W) monoborides in orthorhombic and tetragonal structures. The results of equilibrium structures are in good agreement with other available theoretical and experimental data. The elastic properties, including bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν were calculated by the Voigt-Reuss-Hill approximation. All considered monoborides are mechanically stable. The results of elastic anisotropies show that elastic anisotropy of orthorhombic structure is larger than that of tetragonal structure. Moreover, the minimum thermal conductivities were also estimated using the Cahill’s model, and the results indicate that the minimum thermal conductivities show a dependence on directions.     

辐照诱发中间相Zr(Cr,Fe)2非晶化的原位电子显微研究

 在美国Argonne国家实验室连接有IVEM-Tandem National Facility加速器的Hitatch3000电子显微镜上，通过能量600keV及注量率为2.5×10¹²cm^-2·s^-1的Ne离子原位辐照,研究了锆-4合金中沉淀相hcp Zr(Cr,Fe)₂的重离子辐照效应，结果表明：600keV的Ne离子在350℃原位辐照至0.2dpa时，hcp-Zr(Cr,Fe)₂沉淀相的层错条纹开始消失；0.8dpa时沉淀相的电子衍射斑点大部分消失，发生明显的化学无序；2.7dpa时明场像衬度完全消失，非晶环已非常明显，表明沉淀相已经非晶化。600keV的Ne离子在350℃辐照hcp-Zr(Cr,Fe)₂相非晶化的临界损伤离位率约为2.7dpa。     

NdFe10M2(M=Mo,Cr)渗C(N)化合物的结构和内禀磁性研究

本文采用气—固反应，将Ｃ、Ｎ原子渗入到ＮｄＦｅ₁₀Ｍ₂结构中的间隙位，不改变它们的ＴｈＭｎ₁₂型结构，进而研究了ＮｄＦｅ₁₀Ｍ_xZ_x（ｚ＝Ｃ，Ｎ）的内禀磁性，Ｃ，Ｎ原子对它们的磁性影响不尽相同，其中ＮｄＦｅ₁₀Ｍｏ₂Ｃ_0.8有单轴各向异性，磁晶各向异性场Ｈ_s＝１１６．０ｋＯｅ。最后对样品进行了穆斯堡尔谱测量，研究了它们的超精细场特性。 关键词：