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1.
Accumulating evidence for a two-step magnetic ordering in the borocarbide DyNi2B2C is summarized, including earlier overlooked evidence for the initial magnetic transition and a recent magnetization study of polycrystalline samples. The two-step ordering involves initial two-dimensional ferromagnetic ordering in the DyC (basal) planes at TN (=16.3 K), gradual build-up of the three-dimensional (3D) alternate stacking of ferromagnetic planes, and a final 3D ordering in the AF–I-related structure at a lower temperature To (=10.4 K), depicting a first-order transition. Supporting evidence for the two-step magnetic ordering in DyNi2B2C comes from point-contact spectroscopy measurements in the normal state for DyNi2B2C–Ag contact, and from similar behaviour of PrNi2B2C and (Pr0.91Dy0.09)Ni2B2C. In the isostructural borocarbide DyCo2B2C the two magnetic transitions (at 7.8 and 2.6 K) deduced from the specific-heat measurements are also attributed to a two-step magnetic ordering.  相似文献   

2.
《Current Applied Physics》2014,14(6):886-891
In this work, the magnetic properties and critical behavior around ferromagnetic–paramagnetic (FM–PM) phase transition in Ba1.7La0.3FeMoO6 compound have been investigated in detail. This compound exhibits a second-order magnetic phase transition with Curie temperature TC = 345 K. The critical exponents β, γ, and δ that are determined by using the modified Arrott plots (MAP), the Kouvel–Fisher (KF) and the critical isotherm analysis agree very well. Our results indicate a coexistence of short-range and long-range ferromagnetic (FM) interactions in Ba1.7La0.3FeMoO6 compound. The existence of long-range FM interactions in this compound can be associated with the crystal structure of materials with long-range Fe/Mo ordering parameter and strength of double-exchange interaction, whereas the existence of the short-range FM interactions can be explained by magnetic inhomogeneity and FM clusters.  相似文献   

3.
We report magnetization and specific heat measurements down to 2?K and electrical resistivity down to millikelvin temperatures on polycrystalline samples of the non-centrosymmetric compound Yb2Co12P7. In addition to the previously reported ferromagnetic ordering of the cobalt sub-lattice at T C ?=?136?K we find a magnetic transition below T M ?=?5?K that is likely associated with ordering of the Yb ions. The broad nature of the specific heat anomaly suggests disordered magnetism and possible short-range correlations well above TM .  相似文献   

4.
Magnetic properties and magnetocaloric effects (MCEs) of the Dy3Co compound are studied. Two successive magnetic transitions: the antiferromagnetic (AFM)-to-AFM transition at T AF =29 K and the AFM-to-paramagnetic (PM) transition with increasing temperature at the Néel temperature T N =44 K are observed. Dy3Co undergoes a field-induced metamagnetic transition from the AFM to the ferromagnetic (FM) state below T N , giving rise to a large MCE. The maximal value of magnetic entropy change ΔS m is −13.9 J/kg K with a refrigerant capacity (RC) of 498 J/kg around T N for a field change of 0–5 T. A sign change of MCE in Dy3Co with magnetic field and temperature is observed near the critical field where the metamagnetic transition occurs.  相似文献   

5.
Polycrystalline Nd1−xKxMnO3 (x=0.10–0.20) compounds have been prepared in single phase form with Pbnm space group. The magnetic properties were studied by measuring dc magnetization and ac susceptibility. They exhibit paramagnetic to ferromagnetic transition with transition temperature ranging from 116 to 128 K. The magnetization data have been analyzed by using Brillouin function model and by taking into account the ferromagnetic interaction. The effective spin contribution towards ferromagnetic interaction and spin canting angle have been estimated. The spin canting angle is found to decrease with increase in doping. Magneto-caloric effect (MCE) has been studied and the maximum change in entropy was found to be 1.76 J/kg K for 1 T field. Metal–insulator transition and colossal magnetoresistance of the order of 60% for 1 T field have been observed for x=0.20 sample.  相似文献   

6.
The results of studying the magnetic and magnetoresonance properties of the diluted magnetic semiconductor Hg0.5Cd0.4Cr0.1Se are presented. Microanalysis of the samples shows that the introduction of cadmium and chromium elements into the host HgSe matrix leads to the formation in the crystal of the four-component compound HgCdCrSe with the high chromium content [Cr (18.96 %)] and the three-component compound HgCdSe. The measured temperature dependence of the crystal magnetization illustrates the transition to ferromagnetic ordering at the Curie temperature T C = 126 K. It is noted that the measured magnetization value points out the indicates the presence of both Cr3+ and Cr2+ ions in the compound HgCdCrSe, which is responsible for the magnetic and magnetoresonance properties of the sample under test. The electron paramagnetic resonance studies are carried out on the an X-band spectrometer in the temperature range 77 K < T < 300 K. The angular dependences of electron paramagnetic resonance spectra are shown in the paramagnetic and ferromagnetic temperature ranges. As follows from the analysis of experimental data, the aforementioned transition is accompanied by the evolution of the electron paramagnetic resonance spectrum at changing the temperature and the orientation of the sample relative to the static magnetic field in the ferromagnetic temperature range. In the assumption of the g-tensor axial symmetry the components of the latter are determined and the different law of their temperature changing is revealed in the ferromagnetic ordering state of the sample.  相似文献   

7.
The structural, transport and electron spin resonance properties of bulk and nanosized La0.875Sr0.125MnO3 prepared by a sol-gel method have been investigated. The bulk sample has an orthorhombic structure and a ferromagnetic insulating ground state. The ESR spectra indicate the coexistence of the ferromagnetic insulating and ferromagnetic metallic phases below TC. In addition to a sharp peak in the vicinity of TC, another sharp peak close to is clearly observed in the intensity of the spectra, which may be correlated with the structural transition and orbital ordering at this temperature. For the nanosized sample, a drastically different behavior is found. With a rhombohedral structure down to 70 K, the nanosized sample shows a ferromagnetic metallic ground state. The ESR studies reveal the coexistence of the paramagnetic and ferromagnetic resonance signals. The resonance intensity shows a broad peak around 200 K, which may be due to the wide ferromagnetic transition in the nanoparticle.  相似文献   

8.
Raman spectroscopy studies are reported for the RuSr2Eu1.5Ce0.5Cu2O10 (Ru-1222) compound at various temperatures of 300, 250, 200 and 90 K. Three distinct vibrational bands: the first at 110, 140, and 160 cm−1, the second at 295 and 347 cm−1, and third one at 651 cm−1 are seen in Raman spectra of the compound at room temperature. These bands are attached to the Cu atoms’ c-direction, the Ru atoms’ ab-plane stretching and Ru atoms’ c-direction anti-stretching modes. Below 200 K, an extra vibrational mode is also seen at 260 cm−1. Also, with a decrease in temperature, though the Cu vibrational modes remain intact, the Ru atoms’ ab-plane stretching (295 cm−1) and c-direction anti-stretching (651 cm−1) modes shift gradually to higher wave number positions. The frequencies of modes at 260 and 651 cm−1 showed anomalous softening and line-width broadening below 100 K that corroborates well with the spin ordering seen in susceptibility studies. The studied compound is a ferromagnetic superconductor with magnetic ordering of the Ru spins at 200 K and superconductivity below 30 K. A magnetic and electrical transport characterization of the compound is also presented briefly.  相似文献   

9.
The influence of interstitial hydrogen on the electronic structure and the itinerant-electron metamagnetic (IEM) transition in strong magnetocaloric compound La(Fe0.88Si0.12)13H1.6 has been investigated by Mössbauer spectroscopy. A slight change in the average hyperfine field at 4.2 K was observed after hydrogen absorption. In contrast, the thermally induced first-order transition related to the IEM transition for y=1.6 appears at the Curie temperature TC=330 K, much higher than TC=195 K for y=0.0. The increase of isomer shift δIS at 4.2 K indicates that the valence electron transfer from hydrogen to Fe is negligibly small, hence the change in the magnetic state is closely associated with a volume expansion after hydrogen absorption. No change in shape by hydrogenation for the Mössbauer spectra in the paramagnetic state has been observed except for a difference in only δIS, indicating the volume expansion by hydrogenation is isotropic. Accordingly, the significant increase of TC by hydrogen absorption is attributed to the magnetovolume effect associated with characteristic feature in IEM compounds. A discontinuous change of ferromagnetic moment, ΔM, around TC has been observed by Mössbauer spectra, as expected from the magnetization measurement. The value of ΔM is slightly decreased by increase of TC after hydrogenation but its magnitude is almost the same due to the stabilization of ferromagnetic moment. As a result, strong magnetocaloric effect is maintained up to room temperature after hydrogenation.  相似文献   

10.
In this study the magnetic properties of Mn0.95Cr0.05As, prepared by mechanical milling, have been investigated. The results suggest that the presence of strains is very important for the magnetic state of the compound. In the presently studied compound, a combined magnetic and structural transition occurs from paramagnetic MnP phase to ferromagnetic NiAs phase at about 234 K. With further decreasing temperature, at 159 K, a transition from ferromagnetic NiAs phase to helimagnetic (Ha-type) MnP phase is observed, which is accompanied by an inverse magnetocaloric effect. The ferromagnetic phase is recovered when the temperature is increased. At both first-order transitions, at 159 and 234 K, large magnetic-entropy changes are observed.  相似文献   

11.
We report an easy single step synthesis route of title compound NdFeAsO0.80F0.20 superconductor having bulk superconductivity below 50 K. The title compound is synthesized via solid-state reaction route by encapsulation in an evacuated (10-3 Torr) quartz tube. Rietveld analysis of powder X-ray diffraction data shows that compound crystallized in tetragonal structure with space group P4/nmm. R(T)H measurements showed superconductivity with T c (R = 0) at 48 K and a very high upper critical field (H c2) of up to 345 T. Magnetic measurements exhibited bulk superconductivity in terms of diamagnetic onset below 50 K. The lower critical field (H c1) is around 1000 Oe at 5 K. In normal state i.e., above 60 K, the compound exhibited purely paramagnetic behavior and thus ruling out the presence of any ordered FeO x impurity in the matrix. In specific heat measurements a jump is observed in the vicinity of superconducting transition (T c ) along with an upturn at below T = 4 K due to the AFM ordering of Nd+3 ions in the system. The Thermo-electric power (TEP) is negative down to T c , thus indicating dominant carriers to be of n-type in NdFeAsO0.80F0.20 superconductor. The granularity of the bulk superconducting NdFeAsO0.8F0.2 sample is investigated and the intra and inter grain contributions have been individuated by looking at various amplitude and frequencies of the applied AC drive magnetic field.  相似文献   

12.
The structural and magnetic ordering in La0.6Ca0.4MnO3 has been studied by neutron powder diffraction as a function of temperature between 15 and 300 K. The para-ferromagnetic transition at T∼250 K is accompanied by significant structural distortions in the form of octahedral Mn–O6 rotations. At 15 K, the total refined ferromagnetic moment on the Mn site was obtained as 3.1 μB, in reasonable agreement with the total expected average moment of mixed Mn3+/Mn4+ matrix.  相似文献   

13.
Magnetization measurements of a La1/3Nd1/3Ca1/3MnO3 perovskite at magnetic field up to 6 T have revealed an anomalous behaviour – above 130 K the material exhibits a loop displacement about a field of 2 T. We assume that this is the result of an exchange interaction between ferromagnetic and antiferromagnetic phases in a magnetically inhomogeneous compound. At about 115 K a transition from a semiconducting to a metallic-like state has been observed.  相似文献   

14.
Lattice constants, electrical resistivity, heat capacity, AC and DC magnetic susceptibility and 151Eu Mössbauer effect studies on a new intermetallic compound, Eu2PdSi3, found to crystallize in an AlB2-derived hexagonal crystal structure, are reported. The results establish that the Eu ions are in the divalent state down to low temperatures, undergoing two magnetic transitions, one at 40 K and the other at 10 K, pertaining to two different Eu sites. Interestingly, the minority Eu ions at the 2(b) sites order at a relatively high temperature (40 K) and this magnetic interaction is inferred to be ferromagnetic and quasi one-dimensional along the c-axis. The magnetic structure below 5 K following magnetic ordering (at 10 K) of the majority ions at 6(h) sites appears to be quite complex. In short, the crystallographic and (hence) the overall magnetic behaviors of this compound present an interesting situation.  相似文献   

15.
The magnetic and thermal properties of the anion-deficient La0.70Sr0.30MnO2.85 manganite are investigated in wide temperature (4–350 K) range, including under hydrostatic pressure (0–1.1 GPa). Throughout the pressure range investigated, the sample is spin glass with diffused phase transition into paramagnetic state. It is established, that spin glass state is a consequence of exchange interaction frustration of the ferromagnetic clusters embeded into antiferromagnetic clusters. The magnetic moment freezing temperature T f of ferromagnetic clusters increases under pressure, freezing temperature dependence on pressure is characterized by derivative value ∼4.5 K/GPa, while the magnetic ordering T MO temperature dependence is characterized by derivative value ∼13 K/GPa. The volume fraction of sample having ferromagnetic state is V fer ∼ 13% and it increases under a pressure of 1.1 GPa by ΔV fer ≈ 6%. Intensification of ferromagnetic properties of the anion-deficient La0.70Sr0.30MnO2.85 manganite under hydrostatic pressure is a consequence of oxygen vacancies redistribution and unit cell parameters decrease. The most likely mechanism of frustrated exchange interactions formation is discussed.  相似文献   

16.
V. P. S. Awana  H. Kishan 《Pramana》2006,66(1):247-250
The Ru0.9Sr2YCu2.1O7.9 compound synthesized by HPHT (high pressure high temperature) solid-state reaction route exhibits bulk superconductivity below 30 K. Also the Ru-spins are ordered magnetically above 143 K, with a ferromagnetic component at 5 K. Low field (<1000 Oe)M vs.H plots show that both the superconducting and ferromagnetic components are present in the compound at 5 K. At low temperatures, the compound though remains in spontaneous vortex phase, itsM vs.H hysteresis loop is symmetric instead of the theoretically expected asymmetric one. Our results cast doubts on either theoretical model or the intrinsic nature of ferromagnetic superconductivity in studied ruthenate.  相似文献   

17.
Dipolar coupling in the body-centered tetragonal crystal of Ising spins that is a prototype of the Mn12Ac molecular magnet favors ferromagnetic ordering below the mean-field Curie temperature 0.71 K. With the help of Monte Carlo on crystals of up to one million Mn12 molecules, it is shown that ordering occurs at 0.36 K in elongated crystals. The resulting state is split into ferromagnetic domains with domain walls preferring the diagonal orientation. Domain walls are pinned by the lattice at low temperatures. Making the crystal shorter makes domains finer and smoothens out the singularity at the ordering transition, decreasing the susceptibility in the domain state.  相似文献   

18.
In this paper we investigate the properties of polycrystalline series of Ru1?xCrxSr2Eu1.5Ce0.5Cu2O10?δ (0.0 ? x ? 0.40) by resistivity, XRD and dc magnetization measurements. EuRu-1222 is a reported magneto superconductor with Ru spins magnetic ordering at temperatures near 100 K and superconductivity occurs in Cu–O2 planes below Tc ? 40 K. The exact nature of Ru spins magnetic ordering is still being debated and no conclusion has been reached yet. In this work, we found the superconducting transition temperature Tc = 20 K from resistivity and dc magnetization measurements for pristine sample. DC magnetization measurements exhibited ferromagnetic like transition for all samples.  相似文献   

19.
Field dependent specific heat measurements and a study of elastic neutron scattering experiments characterize CePd2Ga3 as a ferromagnetic Kondo compound with ordering in the basal plane belowT C 6 K. The crystal field ground state of cerium in this hexagonal compound is the |±1/2> eigenstate. In the scope of a phenomenological model, the coupling constant and the Kondo temperature have been deduced.  相似文献   

20.
We report the magnetocaloric effect in the metamagnetic compound Gd2In obtained from magnetization measurement. Gd2In was previously reported to have two magnetic transitions: (i) a paramagnetic to ferromagnetic transition below 190 K and (ii) a ferromagnetic to an antiferromagnetic state below 105 K. The low temperature antiferromagnetic state is unstable under an applied magnetic field and undergoes metamagnetic transition to a ferromagnetic like state. We observe conventional positive magnetocaloric effect (the magnetic entropy change, ΔSM<0) around 190 K at all applied fields. The magnetocaloric effect is found to be inverse (negative) at low fields around 105 K (ΔSM>0), however it turns positive at higher fields (ΔSM<0). The observed anomaly is found to be related to the field induced transition which drives the system from an antiferromagnetic to a ferromagnetic state.  相似文献   

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