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1.
The stannides RETSn (RE=Gd-Er and T=Cu,Ag), NdPtSb type structure, space group P63mc, have been investigated by 119Sn Mössbauer spectroscopy and specific heat studies. Small transferred magnetic hyperfine fields are detected at the tin nuclei at 4.2 K in the 119Sn Mössbauer spectra of RECuSn (RE=Tb,Dy and Ho) which reveal that these compounds undergo magnetic transitions at low temperatures. Heat capacity (C) measurements show that the title compounds undergo antiferromagnetic ordering. In order to explore the magnetic behaviour below the Néel temperature (TN), the magnetic part of heat capacity was obtained by subtracting the lattice part of heat capacity obtained from the isostructural non-magnetic stannides Y TSn (T=Cu,Ag). of GdCuSn exhibits an equal moment (EM) magnetic structure and also exhibits multiple transitions below TN, revealing higher order exchange interactions. Among the REAgSn stannides, the magnetic part of heat capacity for RE=Dy and Er exhibits non-T3 behaviour at low temperatures.  相似文献   

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The title compound absorbs slowly hydrogen at 523 K under a pressure of P(H2)=1 MPa, giving the new hydride Ce(Ni0.82Cu0.18)SnH1.7(1). The hydrogenation induces both: (i) a structural transition from orthorhombic TiNiSi-type to hexagonal ZrBeSi-type and (ii) a magnetic transition from antiferromagnetic to ferromagnetic ordering This behaviour is compared to that observed recently during the hydrogen insertion into the Kondo semi-metal stannide CeNiSn.  相似文献   

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The magnetic properties of Mg0.95Mn0.05Fe2O4 ferrite samples with an average particle size of ∼6.0±0.6 nm have been studied using X-ray diffraction, Mössbauer spectroscopy, dc magnetization and frequency dependent real χ(T) and imaginary χ(T) parts of ac susceptibility measurements. A magnetic transition to an ordered state is observed at about 195 K from Mössbauer measurements. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization have been recorded at low field and show the typical behavior of a small particle system. The ZFC curve displays a broad maximum at , a temperature which depends upon the distribution of particle volumes in the sample. The FC curve was nearly flat below , as compared with monotonically increasing characteristics of non-interacting superparamagnetic systems indicating the existence of strong interactions among the nanoparticles. A frequency-dependent peak observed in χ(T) is well described by Vogel-Fulcher law, yielding a relaxation time and an interaction parameter . Such values show the strong interactions and rule out the possibility of spin-glass (SG) features among the nanoparticle system. On the other hand fitting with the Néel-Brown model and the power law yields an unphysical large value of τ0 (∼6×10−69 and 1.2×10−22 s respectively).  相似文献   

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The salt 4-benzyl pyridinium dihydrogenmonophosphate is monoclinic P21/c with the following unit cell dimensions: ; ; ; and β=97.328(11). Also, , Dx=1.403, , F(000)=560; ; and R=0.0495 and Rw=0.0964 for 3733 independent reflections. The structure consists of infinite parallel two-dimensional planes built of H2PO4 anions and C6H5CH2C5H4NH+ cations mutually connected by strong O-H ?O and N-H ?O hydrogen bonding. There are no contacts other than the normal Van der Waals interactions between the layers. The conductivity relaxation parameters associated with some H+ conduction have been determined from an analysis of the spectrum measured in a wide temperature range.  相似文献   

9.
Magnetic susceptibility of powder Er2Ti2O7 (ErT) is measured between 300 K and 80 K. shows a Curie-Weiss (CW) type behaviour with   ErTiO3.5 and . A crystal field (CF) analysis of our experimental data, g-values (g=0.27 and g=7.8) and the positions of two CF levels (reported earlier from an inelastic neutron scattering study) provide CF parameters and CF levels of the ground 4I15/2 and excited multiplets of ErT. The theoretical follows a CW-type behaviour, with . Single-ion magnetic anisotropy (χχ) is 9500×10−6 emu/mol ErTiO3.5 at 300 K, which increases by ∼54 times at 10 K and ErT resembles an XY planar system. It can be inferred from CF analysis that the earlier observed change of from −13 K to −22 K below 50 K is not due to the CF effect. Nuclear hyperfine (HF) levels of 167ErT and 166ErT are calculated and the theoretical curve of vs. T (K) for T<TN matches the observed results. Mössbauer lines expected for 166ErT are also predicted.  相似文献   

10.
Low temperature magnetic (M) and thermal (CP) properties of the intermetallic compound Ce2Pd2Sn have been investigated at zero and different magnetic fields. Two transitions were recognized at and , with latter nearly coinciding with the extrapolated Curie-Weiss temperature . The Curie factor evaluated from TTM, is ≈2μB. The positive value of θP, the triangular coordination of the magnetic (Ce) atoms and the weak effect of applied magnetic field, reveal that TM cannot be considered as a canonic antiferromagnetic transition like claimed in the literature. M(T) measurements under moderate magnetic fields () show TC(B) increasing while TM(B) is practically not affected. Both transition merge in a critical point at for , where the intermediate phase is suppressed. At , the cusp of a first order transition is observed in CP(T). According to the proposed ferromagnetic ground state, it is followed by a CP(T)∝T3/2exp(-Eg/T) dependence, with a gap of anisotropy .  相似文献   

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We have investigated the molecular motions of TRIS+ ([(CH2OH)3CNH3]+) and ions in the [(CH2OH)3CNH3]2SiF6 crystal below room temperature from the measurements of the spin-lattice relaxation time T1 and the NMR absorption line of 1H and 19F nuclei, in order to elucidate the changes of the molecular motions by the phase transition of Tc=178 K. The narrowing of the 19F-NMR line was observed around Tc=178 K and the reorientation of the anion appears above Tc. Moreover, from the analysis of the temperature dependence of T1, we have observed that the activation energy of the reorientational motion of ions changes from 0.168 eV (T>Tc) to 0.185 eV (T<Tc). Based on these results, we found that the reorientational motion of ions is closely related to the origin of the phase transition at Tc. In addition, from the measurement of the 1H-NMR line, we also found that the reorientational motion of H2 in the -CH2OH group becomes active accompanied by the phase transition.  相似文献   

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The magnetocaloric effect (MCE) in a magnetic SmNi sample was evaluated from magnetization and heat capacity measurements. The MCE phenomena in the vicinity of magnetic phase transitions in terms of magnetic entropy change, , and adiabatic temperature change, , are reported. Isothermal magnetization measurements at several temperatures around the transition were carried out and used for versusT calculations. A similar dependence of the magnetic entropy change was evaluated from heat capacity Cp(T) measurements under zero field and 5 T. The SmNi system provides magnetic refrigerants that induce an adiabatic cooling of about during the magnetization process with a field of 5 T in the temperature range of 35-45 K. The temperature dependence of Cp(T) is analyzed in terms of the magnetic and the lattice contributions.  相似文献   

14.
Earlier, the linear magnetoelectric effect of chromium sesquioxide Cr2O3 has been determined experimentally as a function of temperature. One measures the electric field-induced magnetization on Cr2O3 crystals or the magnetic field-induced polarization. From the magnetoelectric moduli of Cr2O3 we extract a 4-dimensional relativistic invariant pseudoscalar . It is temperature dependent and of the order of ∼10−4Y0, with Y0 as vacuum admittance. We show that the new pseudoscalar is odd under parity transformation and odd under time inversion. Moreover, is for Cr2O3 what Tellegen's gyrator is for two port theory, the axion field for axion electrodynamics, and the PEMC (perfect electromagnetic conductor) for electrical engineering.  相似文献   

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We report local magnetization measurements on the heavy fermion superconductor CeCoIn5 using a micro-Hall probe. Below a critical point T0 (), the local magnetization shows a clear jump at the superconducting transition temperatures for both Ha and Hc, indicating that the phase transition at the upper critical field Hc2 becomes a first-order phase transition. In addition, we observed an undershoot behavior of magnetization jump above (Hc), which suggests a rapid change of textured superconducting structure with vortices and the nodal planes expected in the Fulde-Ferrell-Larkin-Ovchinnikov state.  相似文献   

17.
The natural cuprate botallackite, Cu2Cl(OH)3, is found to be a new antiferromagnet with Magnetic susceptibility properties under strong field show non-linear M-H properties indicating metamagnetism. The TN and the super-exchange coupling are discussed and compared with its polymorph atacamite and other copper oxides on the basis of their structural parameters.  相似文献   

18.
Effects of doping Na on the structure, electrical and magnetic properties of La2/3Ca1/3MnO3 are investigated. A structural phase transition from orthorhombic to rhombohedral structure takes place at y=0.375. All samples show metal-insulator (M-I) transition at the transition temperature and undergo the transition from paramagnetism to ferromagnetism at the Curie temperature TC. and TC increase monotonically with increasing Na content. However the Na-doped samples have a shoulder in their electrical transport curves found below and shows a widened magnetic transition process. On the other hand, intrinsic colossal magnetoresistance (CMR) peaks are observed in all the samples, but samples with y around 0.25 show two MR peaks which can be attributed to magnetic inhomogeneity induced by the doped Na+ ions. Here we propose a method to broaden the CMR peak of perovskite manganite, which is beneficial for practical applications.  相似文献   

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We have investigated the ferromagnetic resonance (FMR) response of as-made and temperature annealed FePt magnetic nanoparticles. The as-made nanoparticles, which have been fabricated by a chemical route, crystallize in the low magnetic anisotropy fcc phase and have a diameter in the range of 2-4 nm. The annealing of the particles at high temperatures (TA=550, 650 and C) in an inert Ar atmosphere produces a partial transformation to the high magnetocrystalline anisotropy L10 phase, with a significant increase in particle size and size distribution. FMR measurements at X-band (9.5 GHz) and Q-band (34 GHz) show a single relatively narrow line for the as-synthesized particles and a structure of two superimposed lines for the three annealed samples. The origin of this line shape has been attributed to the presence of the disordered fcc phase. Assuming that the system consists of a collection of identical particles with a random distribution of easy axes, we have been able to estimate a mean value for the magnetic anisotropy constant of the particles in the fcc phase, K∼2×106 erg/cm3. The measured line shape in the annealed samples can be explained if we consider that the magnetic anisotropy of the particles has a gaussian distribution with a relatively broad width.  相似文献   

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