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1.
Measurements of the electrical conductivity, magnetoresistance, and Hall effect were performed on a n-type ferromagnetic semiconductor HgCr2?xInxSe4(x = 0.100) single crystal from 6.3 to 296 K in magnetic fields up to 1.19×l06A/m. The conductivity decreases rapidly near the Curie temperatureTc (≈120 K) as the temperature is raised. A large peak in the magnetoresistance is observed near Tc. The Hall effect measurements indicate that the temperature dependence of the conductivity and the magnetoresistance are due mostly to a change in electron mobility. The electron mobility is 1.2 × 10?2 m2/V · s at 6.3 K, and decreases rapidly near Tc with the rise in temperature. Then it increases slowly from 5.5 × 10?4 m2/V · s at 160 K to 7.5 × 10?4 m2/V · s at 241 K. This temperature dependence of the electron mobility can be explained in terms of the spin-disorder scattering which takes into account the exchange interaction between charge carriers and localized magnetic moments.  相似文献   

2.
We have investigated the spin dynamics of a distorted perovskite Eu0.6Sr0.4MnO3 by means of Mössbauer spectroscopy. Below 70 K the exchange interaction grows gradually, and below 42 K the spins turn into a cluster glass state. The magnetic field-induced insulator-to-metal (IM) transition at low temperature is a transition from cluster glass to ferromagnet. The induced metallic phase seems to be still in non-uniform electronic state. On the other hand, at 80 K, just above T c of the induced ferromagnet, a metamagnetic transition was observed.  相似文献   

3.
We have determined the magnetic structure of the intermetallic compound GdGa by 155Gd Mössbauer spectroscopy and neutron powder diffraction. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure. It orders ferromagnetically at T c ?=?190(2) K and then undergoes a spin reorientation at T SR ?=?68(2) K. Between T c and T SR , the magnetic structure is characterized by ferromagnetic order of the Gd moments along the b-axis. On cooling below T SR , the Gd 4c magnetic moments split into two groups (2:2). At 3.6 K, the Gd moment is 6.7(4) μ B , and the Gd magnetic moments are in the bc-plane, canted by 84(3)° and 46(4)° with respect to the crystallographic b-axis. This splitting into two magnetically inequivalent sites is confirmed by our 5 K 155Gd Mössbauer results.  相似文献   

4.
Polycrystalline samples of FeSe0.82 and FeSe0.5Te0.5 were synthesized using a solid-state reaction route. Bulk superconductivity was confirmed using SQUID magnetometry. The onset of T c was at 8.0 K for FeSe0.82 and 12.5 K for FeSe0.5Te0.5. Paramagnetic 57Fe Mössbauer spectra were recorded at temperatures between 5.4 and 320 K in transmission geometry. All spectra exhibited simple quadrupole splitting. For FeSe0.5Te0.5 a small drop in the quadrupole splitting was observed about T c upon cooling. Additionally, for both samples the isomer shift and the total absorption started to drop around T c , indicating a softening of the lattice. The drop is estimated to correspond to at least 60 K from the original Debye temperatures.  相似文献   

5.
La0.67Ca0.33MnO3 particle films with an average particle size of ~150 nm were grown on single-crystal silicon substrate using pulsed electron deposition technique and then focused ion beam was introduced to fabricate nanobridge in size of 300 × 900 nm on the particle film. The magneto-transport properties of both samples were studied. For the film, there is only one resistance peak at 182 K in temperature-dependent resistance (RT) curves, which is far lower than ferromagnetic–paramagnetic transition temperature (T C) of 250 K. When compared to the film, double peaks were observed in both RT curves and magnetoresistance dependent on temperature (MR–T) curves of the nanobridge, one peak is at 186 K, which is very close to metal–insulator transition temperature (T P) of film, the other one is at 250 K, which is close to the T C of film, and these two peaks caused separately by grain and grain boundary (GB), which demonstrated that the electrical transport behavior of grain was separated from that of GB.  相似文献   

6.
Specific heat and magnetization measurements demonstrate that the antiferromagnetic (AFM) phase transition at T N  = 5.7 K of EuTiO3 is rapidly suppressed with Sr doping in Eu x Sr1?x TiO3. Close to x = 0.25, T N  = 0 K and AFM order vanishes. Above this critical concentration a finite transition temperature to an AFM phase is observed. The exchange couplings are derived as a function of x and the corresponding low temperature phase diagram is presented.  相似文献   

7.
Magnetization and Mössbauer studies have been made for understanding magnetic behavior of three double perovskite systems La1.5Ca1.5Mn2???x Fe x O7 corresponding to x = 0.05, 0.10 and 0.50. These have been prepared following sol–gel route. Substitution of Fe does not lead to any major change in the tetragonal cell but increased iron leads to greater distortion in octahedral site. The three samples undergo paramagnetic–ferromagnetic transition. Curie temperature (T c) for the system with 0.05 Fe is ~150 K which is lower than (190 K) for the system without iron; with 0.50 Fe T c goes below 50 K. Iron goes as Fe3?+? and replaces Mn in ab plane. With increasing Fe the valence states of Mn get re-distributed in a way that number of the Jahn–Teller ions Mn3?+? increases and that of the pairs of Mn3?+?–O–Mn4?+? experiencing double exchange decreases.  相似文献   

8.
Extensive studies on the temperature (T) dependent exchange bias effect were carried out in polycrystalline BiFeO3(BFO)/NiFe and BFO/Co bilayers. In contrast to single-crystalline BFO/ferromagnet (FM) bilayers, sharp increase of the exchange bias field (H E ) below 50 K were clearly observed in both of these two bilayers. However, when T is higher than 50 K, H E increases with T and decreases further when T is larger than 230 K (for BFO/NiFe) or 200 K (for BFO/Co), which is similar to those reported in single-crystalline BFO/FM bilayers. After the exploration of magnetic field cooling, the temperature dependent exchange bias can be explained considering two contributions from both the interfacial spin-glass-like frustrated spins and the polycrystalline grains in the BFO layer. Moreover, obvious exchange bias training effect can be observed at both 5 K and room temperature and the corresponding results can be well fitted based on a recently proposed theoretical model taking into account the energy dissipation of the AFM layer.  相似文献   

9.
The group-theoretical study of the structural phase transition to incommensurate state of MgSiF6·6H2O crystals, revealed by the electron paramagnetic resonance (EPR) method, as well as analysis of the EPR results, are presented. The consideration of temperature dependences of Mn2+ admixture ion EPR spectrum symmetry and parameters leads to the conclusion that at T i1 = 370 ± 0.3 K they undergo second-order structural phase transition to incommensurately modulated state, the order parameter of this transition may be the angle of [Mg(H2O)6]2+ octahedra rotation around crystal C 3 axis. At temperature decreasing below T i1 the gradual transformation of plane-wave modulation of lattice displacements into soliton mode occurs, which is interrupted by the first-order phase transition at T i2 = 343 ± 0.3 K accompanied by abrupt decrease in modulation amplitude. At T c = 298.5 ± 0.3 K the first-order improper ferroelastic phase transition into monoclinic phase occurs. The group-theoretical analysis of the phase transition at T i1 in the investigated crystals, carried out for the first time, has shown that the existence of the incommensurately modulated phase is conditioned by the fundamental reasons (presence of Lifshitz invariant). The conclusions of this analysis on the nature of order parameter, the structural motifs of incommensurate phase and the possible character of temperature evolution of the structure are in agreement with the EPR investigation data.  相似文献   

10.
The superconductivity of gold–indium alloys has been investigated using first-principles calculations based on the density functional theory. At ambient pressure, the calculated superconducting transition temperature (T c) is 0.04 μ K in pure gold, but T c dramatically increases by substituting indium atoms for gold atoms. The gold–indium alloy having 12.5 atomic percent indium (Au0.875In0.125) shows T c of 0.1 K, and Au0.75In0.25 marks 1.7 K. The dramatic increase in T c owing to the alloying effect is caused by the enhancement of the electron–phonon coupling. The superconductivity of gold is predicted to be drastically weakened with increasing pressure and virtually disappear at 10 GPa, but it continues up to at least 30 GPa by the inclusion of indium atoms.  相似文献   

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