Magnetic phase diagram for HO-50%tb from anomalies in ultrasonic propagation

Measurements of the elastic constant c₃₃ for Tb-50% Ho, as a function of temperature and magnetic field, have been used to determine the magnetic phase diagram of the alloy. Evidence for the four phases:paramagnetic, spiral spin antiferromagnetic, fan and ferromagnetic are presented. The true ferromagnetic phase is only found below 100 K even in fields of up to 7 Tesla.     

Magnetic phase diagram of very dilute Pd-based alloys

The magnetic phase diagram of Pd-based 3d metal alloys is calculated on the basis of the random molecular field model. A paramagnetic-spin glass transition is expected for c < 0.06 at %, a paramagnetic-ferromagnetic one for c > 0.17 at %, while in the intermediate region a paramagnetic-ferromagnetic-spin glass transition is predicted.     

Theoretical justification of the magnetic phase diagram of CuMn alloys

Some important observations on the magnetic susceptibility of concentration Cumn alloys by Gibbs et al. are reinterpreted in the light of the mean-field theory of classical vector spin models with competing exchange interactions. The phase diagram proposed by Gibbs et al. is shown to be in qualitative agreement with the corresponding phase diagram predicted by mean-field theory.     

A study of the Al-Cu-Co phase diagram and the solidification of alloys containing decagonal phase

The ternary Al-Cu-Co phase diagram was studied in order to revise the region of 50–75 at.% Al. The study was carried out by optical microscopy, scanning electron microscopy, transmission electron microscopy and powder X-ray diffraction. Isothermal 800°C, 600°C and 540°C sections are presented. The development of the composition range of the decagonal phase with temperature is discussed.     

Sound propagation and relaxation processes in the isotropic phase of cholesteryl miristate

The propagation and absorption of high-frequency sound in the isotropic phase of cholesteryl miristate is studied in a wide frequency range using the data of both Brillouin spectroscopy and acoustooptic measurements. The parameters of the relaxation process associated with the volume viscosity relaxation are calculated using the experimental data on the velocity and absorption of sound.     

Predicting the solid state phase diagram for glass-forming alloys of copper and zirconium

The free energies of six crystal structures associated with Cu-Zr alloys-Cu (face centred cubic), Cu(2)Zr, Cu(10)Zr(7), CuZr, CuZr(2) and Zr (hexagonal close packed)-are calculated using the embedded atom potential of Mendelev et al (2009 Phil. Mag. 89 967). We find that the observed low temperature stability of the Cu(10)Zr(7) and CuZr(2) phases is not reproduced. Instead, the model predicts that the CuZr phase remains stable down to T = 0 K. This discrepancy is largely removed when the interaction potentials are cut off at a short distance, such as that used by Duan et al (2005 Phys. Rev. B 71 224208). We present evidence, however, that the cut-off distance necessary to achieve the change in phase stability results in pathological artefacts in the energetics of some crystal phases.     

Magnetic phase diagram of ordered (Fe1-xMnx)Pt alloys

The magnetic structure and magnetic phase transitions of ordered (Fe_1-xMn_x)Pt alloys were investigated by neutron diffraction in the temperature range 4.2–900 K. A complete magnetic phase diagram is drawn up, where the regions for different magnetic states and the character of transitions between them are shown. The theoretical analysis of the magnetic phase stability is given.     

Magnetic phase diagram of γ-FeNiMn alloys with a mixed exchange interaction

The magnetic phase diagram of (Fe_cNi_85?c)Mn₁₅, (Fe_cNi80?c)Mn₂₀ alloys with f.c.c. structure has been determined. The ground state in the transition region between ferromagnetism and antiferromagnetism is found to be either a ferro-spin-glass mixed phase or a spin glass phase. The general feature of the magnetic phase diagram is in good agreement with recent theoretical calculations [2–10].     

Phase diagram of Cu-Au-type alloys

We investigate the ordering phase diagram of an binary alloy on a face centered cubic lattice. In Ising spin language the nearest-neighbor interactions are antiferromagnetic with strengthJ, the next-nearest-neighbor interactions are ferromagnetic with strength J, and the external magnetic field ish. For > 0 and allh, the ground state is only finitely degenerate, so Pirogov-Sinai theory gives the exact form of the phase diagram in the limit of vanishing temperature. For=0 and vhv 12J the ground state is infinitely degenerate, and indeed the zero temperature entropy is nonvanishing at the four super-degenerate pointsh=± 47 or ±1Z7. We investigate the finite temperature behavior of the model using Monte Carlo simulations and (for=0) low temperature expansions. The most interesting portions of the phase diagram are those near the superdegenerate points. We rigorously map these points onto certain hard constraint lattice gases, but can draw no firm conclusions concerning the phase diagram in their vicinity.Supported in part by the National Science Foundation through Grant No. DMR81-14726. The simulations were carried out at the Center for Materials Science at Los Alamos National Laboratory.     

Pressure effect on the magnetic phase diagram of Hf1-xTaxFe2 alloys

Abstract

The lattice constants of Hf_1-xTa_xFe₂ with C14 structure were measured at room temperature under pressure up to 5 GPa. The magnetic phase diagram obtained as a function of pressure was compared with that obtained as a function of Ta concentration x. It is shown that changes in lattice constants by applying pressure and /or by substituting Ta for Hf affect remarkably the magnetic phase stability, which is consistent qualitatively with a recent theoretical prediction based on the local spin density approximation.     

The effect of pressure on magnetization and magnetic phase diagram of monocristals of Tb-Dy alloys

Abstract

The effect of pressure on magnetic phase transitions in monocrystals of Tb-Dy alloys is studied. It is shown that the destruction of antiferromagnetic structure and the establishment of ferromagnetic ordering is due to magneto-elastic interactions.     

Phase diagram and magnetocaloric effect of alloys

We propose the phase diagram of a new pseudo-ternary compound, CoMnGe_1-xSn_x, in the range x0.1. Our phase diagram is a result of magnetic and calorimetric measurements. We find that the separate magnetic and structural transitions in CoMnGe are tuned together as the level of Sn substitution is increased. We demonstrate the appearance of a hysteretic magnetostructural phase transition in the range x=0.04–0.055, similar to that observed in CoMnGe under hydrostatic pressure. From magnetisation measurements, we show that the isothermal entropy change associated with the magnetostructural transition can be as high as in a field of 1 T. However, the large thermal hysteresis in this transition () will limit its straightforward use in a magnetocaloric device.     

微晶玻璃中的声传播

本文把悬浮液中的声学处理方法应用到微晶玻璃中,导出了微晶玻璃中声速和声衰减系数随结晶度变化的表达式,并通过实验进行了证实。     

Sound propagation through vegetation

The propagation of sound through a large number of scatterers (i.e., trees) is treated in a similar way to a classical diffusion problem. A general differential equation governing the sound intensity is derived which is valid under certain conditions, notably that the depth of the belt of vegetation is large, and absorption small. The predictions of this theory are compared with results derived from a small scale model study, and with some field measurements. They are also compared with published field data. The implications of some of the conclusions reached for the practical achievement of effective sound attenuation are pointed out. In general, it would appear that significant noise reductions may be achieved for a predominantly high frequency source if the existing ground cover is acoustically hard, or if there is no “ground effect” attenuation between source and receiver for some other reason. In other cases, the noise reduction will be much lower and may be negative.     

Sound wave anomalies in superconducting compounds

Temperature dependence of the elastic constants in the superconducting state is described on the basis of the Ginsburg-Landau theory. This approach shows very general character and allows to describe quantitative renormalization of the elastic constants in the superconducting state for different materials including non-conventional superconductors. Various examples (A-15 compounds, Chevrel compounds, CeRu₂, Ba_0.63K_0.37BiO₃, Yb₃Rh₄Sn₁₃, Ca₃Rh₄Sn₁₃, HfV₂, some heavy fermion compounds and Sr₂RuO₄) are given.