Papers by Keyword: Magnetic Transition

Abstract: In this work, the fourth element Cu was introduced to substitute Ni in polycrystalline Ni-Mn-Sn alloys. It was shown that Cu doping did not change the crystal structure of the martensite in Ni_50-xCu_xMn₃₉Sn₁₁ (x=0, 1, ......,7) alloys, but resulted in the decrease of martensitic transformation temperatures. Due to the higher atomic radius of Cu with respect to that of Ni, the lattice volume of martensite unit cell increases with the gradual substitution of Ni by Cu. For the alloys with the Cu content of 0-4%, the martensitic transformation is from weak magnetic (paramagnetic) austenite to weak magnetic (paramagnetic) martensite. When the Cu content is higher than 4%, the paramagnetic to ferromagnetic transition of austenite was introduced. The temperature interval between magnetic transition and structural transformation was enlarged with the increase of Cu content. Due to the relatively smaller magnetization difference between austenite and martensite, the field induced inverse martensitic transformation behavior is not significant in the present Cu-doped alloys.

Abstract: Four alloys with nominal compositions Ni₄₆Mn_41.5-xFe_xSn_12.5 (x=0, 2, 4, 6 at.%) were cast in an induction vacuum furnace and homogenized. Then they were melted in quartz tubes and ejected onto a rotating copper wheel to produce ribbons. The X-Ray phase analyses of as melt spun ribbons have shown that in both, the ternary as well as in the quaternary alloys a single phase of the Heusler L2₁ type ordered structure was found. The characteristic temperatures of magnetic (T_C) and martensitic (M_s) transformations were determined by a vibrating sample magnetometer (VSM). Both the M_s and T_C increase with the increase of Fe content in all alloys, which is in accordance with the theory of valence electron concentration (e/a) influence on M_s. The phase structures, chemical compositions, grains sizes and type of microsegregation were characterized by transmission electron microscope (TEM). The equi-axed grains of size from 0.95 to 1.7 μm were observed in all ribbons. The grains posses the L2₁ structure at room temperature, however in the alloys with higher Fe content the different type of martensite was observed at the grain boundaries of L2₁ phase. Appearance of this martensite was explained in relation to microsegregation of particular elements during melt spinning process and simultaneous change in the e/a ratio.

Abstract: Many quantum optical and optoelectronic achievements have been obtained by using quantum coherence effects occurred in four-level quantum systems. Here we report a systemic study on the 1^st, 2^nd and 3^rd order subschemes of the four-level scheme with the aid of Boolean algebra, and find 7 1^st order subschemes and 53 2^nd order subschemes in total. Further it is found that 472 3^rd-order subschemes may appear in the realistic optical quantum coherence experiments when the applied lasers are distinguished only by the strong and weak field intensities.

Abstract: The low temperature (T) Raman spectroscopic study on the geometrically frustrated clinoatacamite γ-Cu₂(OH)₃Cl is reported. By measuring the T-dependent spectral profiles and representative modes, we have obtained auxiliary evidence of successive magnetic transitions near T_c1 =18.1 K and T_c2 =6.4 K determined accurately by the magnetic experiments in the Raman band frequencies and peak widths of the representative modes for magnetic research conclusions and observed a pronounced Raman spectroscopy background featuring a broad continuum at all Ts. A quantitative analysis reveals spin fluctuations on a picosecond time scale in the intermediate phase.

Abstract: This work is dedicated to simulate the spinodal decomposition of Fe-Cr bcc (body centered cubic) alloys using the phase field method coupled with CALPHAD modeling. Thermodynamic descriptions have been revised after a comprehensive review of information on the Fe-Cr system. The present work demonstrates that it is impossible to reconcile the ab initio enthalpy of mixing at the ground state with the experimental one at 1529 K using the state-of-the-art CALPHAD models. While the phase field simulation results show typical microstructure of spinodal decomposition, large differences have been found on kinetics among experimental results and simulations using different thermodynamic inputs. It was found that magnetism plays a key role on the description of Gibbs energy and mobility which are the inputs to phase field simulation. This work calls for an accurate determination of the atomic mobility data at low temperatures.

Abstract: Two cases of anomalous phase transitions in Ce intermetallics are presented. In CeIn2 multiple signatures of a first order paramagnetic-ferromagnetic transition at 22 K have been experimentally detected. We discuss possible mechanisms for such behaviour and the new studies in the La1-xCexIn2 series. In the he case of CeNi1-xCux the low temperature ferromagnetic long range order appears owing to a magnetic cluster percolation process, from a cluster glass state established above the ferromagnetic state.

Abstract: The Mn3XN(X=Zn, Cu, Sn) compounds and their solid solutions with anti-perovskite structure were prepared by solid state reaction. Their magnetic transition and simultaneous abnormal thermal expansion behaviors were studied by SQUID and variable temperature X-ray diffraction. The lattice contraction was found in Mn3Cu0.5Sn0.5N and Mn3Zn0.5Sn0.5N during the magnetic transition process, however not in pure Mn3XN(X=Zn, Cu, Sn). The mechanism is discussed, combined with the different doping effects. It seems that the lattice contraction behavior is sensitive to the number of valence electrons at the X site in Mn3XN series.

Abstract: Within the framework of the lattice-statics and static fluctuation-waves’ methods, the available energiesof strain-induced interaction of interstitial–interstitial, interstitial–substitutional and substitutional–substitutional impurity atomic pairs are collected and analysed for f.c.c.-(Ni,Fe)–C solutionsallowing for discrete atomic structure of the host-crystal lattice. The lattice spacings, elasticity moduliand/or quasi-elastic force parameters of the host-crystal lattice, and concentration coefficients of thedilatation of solid-solution lattice due to the respective solutes are selected as the input numerical experimentaldata used. The above-mentioned interaction energies prove to have non-monotonically decreasing(‘quasi-oscillating’) and anisotropic dependences on discrete interatomic radius-vector, andthemselves are strong and long-range. In all f.c.c.-(Ni,Fe)-base solutions, there is strain-induced attractionin many co-ordination shells. In general, the strain-induced interaction between impurity atomsin γ-Fe is weaker than in α-Ni (but in some solid solutions, it may prove to be of the same order).The verification of applicability of the approximation of strain-induced interaction of impurities forf.c.c.-(Ni,Fe)–C alloys (by means of analysis of thermodynamic C activity and ‘short-range order’ parametersof C-atoms’ distribution revealed by Mössbauer spectroscopy) showed that it must be supplementedwith additional short-range (‘electrochemical’) repulsion in the first co-ordination shell.Nevertheless, in any case, the strain-induced interaction of impurity atoms must be taken into accountfor analysis of structure and properties of f.c.c.-(Ni,Fe)-base solutions.

Abstract: Ln2MnNiO6 were synthesized by the usual ceramic method for Ln = Sm, Eu, Gd, Tb and Dy and by the wet method for Ln = La, Nd Ho and Er. Heat capacities of these compounds were measured by using DSC and ACC. The thermal anomalies accompanying by magnetic transition from ferromagnetism to paramagnetism were observed for some rare earths and the magnetic contribution of heat capacity was estimated