共查询到20条相似文献,搜索用时 31 毫秒
1.
Makoto Tachibana 《Solid State Communications》2004,131(12):745-748
Hg2Os2O7, which has the cubic pyrochlore structure, remains metallic down to the liquid helium temperature unlike its isostructural counterpart Cd2Os2O7, which shows metal-insulator transition at 226 K. Magnetization and heat capacity data for Hg2Os2O7 are presented. The magnetic anomaly at TN=88 K shares many characteristics in common with the metal-insulator transition in Cd2Os2O7, though Hg2Os2O7 remains metallic below TN. The heat capacity Cp shows no or very little change in the magnetic entropy around TN, supporting the view that there is no long-range ordering of localized spins. The measured value of electronic heat-capacity coefficient γ=21 mJ K−2mol−1 is comparable to the value obtained from band-structure calculation on Cd2Os2O7, suggesting that mass-enhancement is small in Hg2Os2O7. There is a pronounced peak in Cp/T3 at 13.1 K, which corresponds to a peak in the phonon density of states at 40 cm−1. 相似文献
2.
E.V. Sampathkumaran Niharika Mohapatra Kartik K. Iyer C.D. Cao W. Löser G. Behr 《Journal of magnetism and magnetic materials》2008
Considering certain interesting features in the previously reported 166Er Mössbauer effect, and neutron diffraction data on the polycrystalline form of ErPd2Si2 crystallizing in the ThCr2Si2-type tetragonal structure, we have carried out magnetic measurements (1.8–300 K) on the single crystalline form of this compound. We observe significant anisotropy in the absolute values of magnetization (indicating that the easy axis is c-axis) as well as in features due to magnetic ordering in the plot of magnetic susceptibility χ versus temperature T at low temperatures. The χ(T) data reveal that there is a pseudo-low-dimensional magnetic order setting in at 4.8 K, with a three-dimensional antiferromagnetic order setting in at a lower temperature (3.8 K). A new finding in the χ(T) data is that, for H∥〈1 1 0〉 but not for H∥〈0 0 1〉, there is a broad shoulder in the range 8–20 K, indicative of the existence of magnetic correlations above 5 K as well, which could be related to the previously reported slow-relaxation-dominated Mössbauer spectra. Interestingly, the temperature coefficient of electrical resistivity is found to be isotropic; no feature due to magnetic ordering could be detected in the electrical resistivity data at low temperatures, which is attributed to magnetic Brillioun-zone boundary gap effects. The results reveal the complex nature of magnetism of this compound. 相似文献
3.
Temperature and field-dependent magnetization measurements on polycrystalline CeMnCuSi2 reveal that the Mn moments in this compound exhibit ordering with a ferromagnetic (FM) component ordered instead of the previously reported purely antiferromagnetic (AFM) ordering. The FM ordering temperature, Tc, is about 120 K and almost unchanged with external fields up to 50 kOe. Furthermore, an AFM component (such as in a canted spin structure) is observed to be present in this phase, and its orientation is modified rapidly by the external magnetic field. The Ce L3-edge X-ray absorption result shows that the Ce ions in this compound are nearly trivalent, very similar to that in the heavy fermion system CeCu2Si2. Large thermomagnetic irreversibility is observed between the zero-field-cooled (ZFC) and field-cooled (FC) M(T) curves below Tc indicating strong magnetocrystalline anisotropy in the ordered phase. At 5 K, a metamagnetic-type transition is observed to occur at a critical field of about 8 kOe, and this critical field decreases with increasing temperature. The FM ordering of the Mn moments in CeMnCuSi2 is consistent with the value of the intralayer Mn–Mn distance RaMn–Mn=2.890 Å, which is greater than the critical value 2.865 Å for FM ordering. Finally, a magnetic phase diagram is constructed for CeMnCuSi2. 相似文献
4.
H.D. Yang I.P. HongF.H. Hsu H.H. LiS.Y. Tu H.L. HuangS. Chatterjee S. MollahY.-K. Kuo T.I. HsuH.C. Ku W.-H. Li 《Solid State Communications》2003,127(3):229-232
The specific heat (C) of bi-layered manganites La2−2xSr1+2xMn2O7 (x=0.3 and 0.5) is investigated for the ground state of low temperature excitations. A T3/2 dependent term in the low temperature specific heat (LTSH) is identified at zero magnetic field and suppressed by magnetic fields for x=0.3 sample, which is consistent with a ferromagnetic metallic ground state. For x=0.5 sample, a T2 term is observed and is consistent with a two-dimensional (2D) antiferromagnetic insulator. However, it is almost independent of magnetic field within the range of measured temperature (0.6-10 K) and magnetic field (6 T). 相似文献
5.
S. Baran A. Szytu?a A. Pikul P. Piekarz S. Gerischer 《Journal of magnetism and magnetic materials》2010,322(1):12-18
ErCu2Si2 crystallises in the tetragonal ThCr2Si2-type crystal structure. In this paper results of magnetometric, electrical transport, specific heat as well as neutron diffraction are reported. Results of electrical resistivity and specific heat measurements performed at low temperature yield existence of magnetic ordering roughly at 1.3 K. These results are in concert with neutron diffraction measurements, which reveal simple antiferromagnetic ordering between 0.47 and 1.00 K. At temperatures ranging from 1.00 up to 1.50 K an additional incommensurate magnetic structure was observed. The propagation vector k=(0;0;0.074) was proposed to describe magnetic reflections within the amplitude modulated magnetic structure. Basing on specific heat studies the crystal field levels splitting scheme and magnetic entropy were calculated. 相似文献
6.
R.R. Doshi P.S.R. Krishna D.G. Kuberkar 《Journal of magnetism and magnetic materials》2009,321(19):3285-3289
We report the results of the temperature-dependent neutron diffraction measurements on the nearly half-doped (La0.325Tb0.125)(Ca0.3Sr0.25)MnO3 manganite sample. The simultaneous doping of magnetic Tb3+ and divalent Sr2+ in the La0.7Ca0.3MnO3 system results into a large A-site size disorder. Rietveld refinement of neutron diffraction data reveal that the single phase sample crystallizes in a distorted orthorhombic structure. Increased 〈rA〉 value affects the transport behavior that results into an insulating-like behavior of the sample. Under application of 1 T field sample exhibit insulating-like behavior while insulator-metal transition (TIM) is exhibited under 5 and 8 T fields. Variable range hoping (VRH) mechanism of charge carriers is exhibited in the insulating region. Field cooled and zero field cooled magnetization measurement shows the Curie temperature (TC)~47 K. The refinement of the ND data collected at various temperatures below 300 K shows that there is no structural phase transition in the compound. Around 100 K, a magnetic peak appears at lower angle that can be ascribed to the presence of the A-type antiferromagnetic (AFM) phase. Two more peaks are observed around 50 K at lower angles that can be fitted in CE-type antiferromagnetic phase. Splitting of the peaks at lower temperatures is the signature of orbital ordering in the presently studied nearly half-doped manganite system. Results of the detailed structural analysis of the temperature-dependent ND measurements on (LaTb)0.45(CaSr)0.55MnO3 sample has been discussed in the light of coexisting A-type and CE-type antiferromagnetic phases present in the sample at low temperature. 相似文献
7.
Low-temperature neutron diffraction measurements were carried out on a powder sample of the compound La0.75Sr0.25CrO3 in order to elucidate its magnetic structure. Rietveld analysis of the neutron diffraction data, as a function of temperature, showed that it possesses a G-type antiferromagnetic alignment of Cr spins at all temperatures below 300 K. Down to the lowest achievable temperature, viz. 17 K, the Cr site moments were found to be the weighted average of the 75% Cr3+ and 25% Cr4+ spin-only ionic moments. At 17 K, the Cr site moment was 2.71(5) μB/Cr ion. There is no observable change in the Cr–O bond lengths as a function of temperature. The tilt angles of the CrO6 octahedra marginally increase with decreasing temperature. 相似文献
8.
In this work neutron diffraction studies of Tb2Rh3Si5 compound are reported. The compound crystallizes in the monoclinic crystal structure of Lu2Co3Si5-type. At 1.5 K an antiferromagnetic ordering with a propagation vector k=(1/2;1/2;1/2) was observed. The Tb magnetic moments of 9.8(2) μB form a non-collinear magnetic structure. In the vicinity of Néel temperature of 8 K a change of the magnetic ordering is evidenced. The change seems to be connected with phase transition from commensurate to incommensurate sine-wave modulation of the Tb magnetic moments. 相似文献
9.
G.V. Bazuev A.V. Korolyov T.I. Chupakhina 《Journal of magnetism and magnetic materials》2010,322(5):494-312
Two methods—the solid-phase high-temperature (1300 °C) and the liquid-phase low-temperature (750 °C) routes—were used to synthesize the complex oxide La1.25Sr0.75MnCoO6, which has the structure of rhombohedral perovskite and is characterized by a disordered distribution of Mn and Co in structural sites. It was found by means of X-ray absorption near edge spectroscopy (XANES) at the K-edge that mixed valence states of Co2+/Co3+ and Mn3+/Mn4+, exist in both phases. Measurements of dc magnetization and real (χ′) and imaginary (χ″) parts of the ac susceptibility showed that the magnetic properties of these oxides are determined by a ferromagnetic transition at TC=217 K and a frequency-dependent transition at Tg<100 K. The high frequency dependence of Tg is indicative of the cluster-glass behavior of La1.25Sr0.75MnCoO6 (7 5 0) at T<TC within the ferromagnetic state. 相似文献
10.
The zero-field heat capacity shows an antiferromagnetic ordering of Gd3+ in gadolinium orthophosphate at 0.8 K. The application of the external magnetic field leads to the splitting of the Gd3+ ground-state multiplet. The antiferromagnetic ordering becomes gradually suppressed with increasing field, and the loss of the long-range magnetic ordering with a threshold field between 0.2 and 0.5 T is indicated by heat-capacity data. Estimated entropy of the anomaly due to magnetic ordering or the Schottky-type anomaly (above 0.5 T) is close to Rln8 as expected for Gd3+ ground-state multiplet. Magnetization measurements above 2 K corroborate this magnetic behaviour. 相似文献
11.
Ali Rostamnejadi Hadi Salamati Parviz Kameli Hossein Ahmadvand 《Journal of magnetism and magnetic materials》2009,321(19):3126-3131
Magnetic nanoparticles of La0.67Sr0.33MnO3 (LSMO) manganite were prepared by sol-gel method. Phase formation and crystal structure of the synthesized powder were examined by the X-ray diffraction (XRD) using the Rietveld analysis. The mean particle size was determined by the transmission electron microscopy (TEM). Infrared transmission spectroscopy revealed that stretching and bending modes are influenced by calcinations temperature. The temperature dependence of the ac magnetic susceptibility was measured at different frequencies and ac magnetic fields in the selected ranges of 40-1000 Hz and 80-800 A/m, respectively. The temperature dependence of ac susceptibility shows a characteristic maxima corresponding to the blocking temperature near room temperature. The frequency dependence of the blocking temperature is well described by the Vogel-Fulcher law. By fitting the experimental data with this law, the relaxation time τ0=1.7×10−12 s, characteristic temperature T0=262±3 K, anisotropy energy Ea/k=684±15 K and effective magnetic anisotropy constant keff=2.25×104 erg/cm3 have been obtained. dc Magnetization measurement versus magnetic field shows that some of LSMO nanoparticles are blocked at 293 K. The role of magnetic interparticle interactions on the magnetic behavior is also investigated. 相似文献
12.
Elena Fertman Anatoly Beznosov Vladimir Desnenko Alexander Feher 《Journal of magnetism and magnetic materials》2009,321(4):316-320
The shifts of the magnetic and charge ordering transition temperatures caused by Nd substitution for Y in Nd2/3Ca1/3MnO3 CMR narrow-band perovskite manganite have been studied. At low temperatures, three different long-range magnetic orderings consistent with a phase separation scenario have been observed in the doped compound (Nd0.9Y0.1)2/3Ca1/3MnO3 by neutron-diffraction study: the antiferromagnetic orderings of PCE and DE types existing below ∼110 and ∼60 K, respectively, and the ferromagnetic one of B type existing below ∼42. Magnetic phase transformations temperatures as well as those of charge ordering have been found to be structural-dependent. Y-doping leads to the decrease of the anisotropy of the orthorhombic Pnma crystal lattice b/√2c, which causes a decrease of the indirect exchange parameters in the system and thus a decrease in the magnetic transformation temperatures for 20-30 K in the doped compound. Doping leads as well to the higher level of the coherent Jahn-Teller distortions of the MnO6 octahedra in the 200-300 K temperature region, which results in the increase of the charge ordering temperature for ∼80 K. 相似文献
13.
Temperature dependence of conduction noise and low field magnetoresistance of layered manganite La1.4Ca1.6Mn2O7 (DLCMO) are reported and compared with the infinite layered manganite La0.7Ca0.3MnO3 (LCMO). The double layered manganite was prepared using standard solid state reaction method and had a metal-insulator transition temperature (TM-I) of 155 K. The temperature dependence of susceptibility showed evolution of ferromagnetic ordering at 168 K. The observed voltage noise spectral density (SV) shows 1/fα type of behaviour at all temperatures from 77 K to 300 K. In the ferromagnetic region (T<168 K), SV/V2 shows two peaks at 164 K and 114 K. The observed two peaks in normalised conduction noise of DLCMO is attributed to the excess noise generated due to setting up of short range 2D-ferromagnetic ordering and long range 3D-ferromagnetic ordering at two different temperatures TC2 and TC1. In temperature range between TC1 and TC2, the magnetoresistance (MR) showed a gradual increase with the magnetic field. The observed MR has been explained in the framework of the two phase model [ferromagnetic (FM) domains and paramagnetic (PM) regions]. 相似文献
14.
K. Ramesh Kumar N. Harish Kumar G. Markandeyulu J. Arout Chelvane V. Neu P.D. Babu 《Journal of magnetism and magnetic materials》2008
Polycrystalline Mn2VGa samples were synthesized using an arc furnace. X-ray diffraction (XRD) pattern was analyzed using General Structural Analysis System (GSAS) package and the refined lattice parameter was found to be 5.905 Å. We found magnetic ordering in the system below 783 K and the spontaneous magnetization was observed to be following the Bloch T3/2 law below 80 K. The magnetic moment per formula unit at 5 K was observed to be 1.88 μB. The temperature variation of the electrical resistance was found to follow the relation Rn=R0n+aTα (α=1.616) and (Rn—normalized electrical resistance) in the temperature range of 25–300 K and we observed almost a temperature independent variation of the electrical resistance below 25 K indicating the absence of spin-flip scattering. 相似文献
15.
R. Ortega-Zempoalteca R. Valenzuela 《Journal of magnetism and magnetic materials》2009,321(19):3159-3163
The thermomagnetic behaviour (within the temperature range 553-300 K) for the bulk composite Nd60Fe30Al10 alloy is described in terms of a transition from paramagnetic to superferromagnetic state at T=553 K, followed by a ferromagnetic ordering for T<473 K. For the superferromagnetic regime, the alloy thermomagnetic response was associated to a homogeneous distribution of magnetic clusters with mean magnetic moment and size of 1072 μB and 2.5 nm, respectively. For T<473 K, a pinning model of domain walls described properly the alloy coercivity dependence with temperature, from which the domain wall width and the magnetic anisotropy constant were estimated as being of ≈8 nm and ≈105 J/m3, typical values of hard magnetic phases. Results are supported by microstructural and magnetic domain observations. 相似文献
16.
Z. Hossain A.K. Rajarajan C. Geibel 《Journal of magnetism and magnetic materials》2009,321(3):213-215
The magnetic properties of polycrystalline PrRh2Si2 sample have been investigated by neutron diffraction measurements. Antiferromagnetic transition with an anomalously high ordering temperature (TN∼68 K) is clearly observed in magnetic susceptibility, specific heat, electrical resistivity and neutron diffraction measurements. Neutron diffraction study shows that Pr3+ ions carry an ordered moment of 2.99(7)μB/Pr3+ and align along the crystallographic±c-directions for the ions located at the (0,0,0) and positions. The magnetoresistance at 2 K and 10 T is rather large (∼35%). 相似文献
17.
X.J. Liu Z.Q. Li A. Yu M.L. Liu W.R. Li B.L. Li P. Wu H.L. Bai E.Y. Jiang 《Journal of magnetism and magnetic materials》2007
We have investigated the magnetic, electrical transport and electron spin resonance (ESR) properties of polycrystalline Fe-doped manganite LaMn0.7Fe0.3O3+δ prepared by sol–gel method. A typical cluster-glass feature is presented by DC magnetization and AC susceptibility measurements and a sharp but shallow memory effect was observed. Symmetrical Lorentzian lines of the Mn/Fe spectra were detected above 120 K, where the sample is a paramagnetic (PM) insulator. When the temperature decreases from 120 K, magnetic clusters contributed from ferromagnetic (FM) interaction between Mn3+ and Mn3+/Fe3+ ions develop and coexist with PM phase. At lower temperature, these FM clusters compete with antiferromagnetic (AFM) ones between Fe3+ ions, which are associated with a distinct field-cooled (FC) effect in characteristic of cluster-glass state. 相似文献
18.
J. López 《Solid State Communications》2006,139(6):273-277
Magnetization and specific heat measurements, as a function of temperature, were performed on single crystals of La1.35Sr1.65Mn2O7 and La1.5Sr0.5NiO4, under different applied magnetic fields (H). The specific heat in La1.35Sr1.65Mn2O7 was decreased for H=9 T parallel to the crystal c axis, compared with H=0, possibly due to a suppression of spin-wave excitations (magnons) in that ferromagnetic bilayer structure. On the other hand, the applied magnetic field had no effect in the specific heat of the antiferromagnetic La1.5Sr0.5NiO4. For H=9 T and below the temperature of 4 K the specific heat data, for each crystal, was well fitted by an exponential decay law. This allowed the calculation of energy gaps around 1 meV for both compounds, in close agreement with Δ=2μBH for an expected energy gap in the magnon spectrum. Detailed magnetization measurements showed monotonic variations below 4 K and a steep increase close to 2 K. Both magnetization and specific heat measurements suggest the existence of an anisotropy gap in the energy spectrum of La1.35Sr1.65Mn2O7 and La1.5Sr0.5NiO4. 相似文献
19.
A. Szytu?a ?. Gondek A. Arulraj B. Penc 《Journal of magnetism and magnetic materials》2009,321(20):3402-3405
Physical properties of NdAu2Ge2, crystallising with the tetragonal ThCr2Si2-type crystal structure, were investigated by means of magnetic, calorimetric and electrical transport measurements as well as by neutron diffraction. The compound exhibits antiferromagnetic ordering below TN=4.5 K with a collinear magnetic structure of the AFI-type. The neodymium magnetic moments are parallel to the c-axis and amount to 1.04(4) μB at 1.5 K. The observed magnetic behaviour is strongly influenced by crystalline electric field effect. 相似文献
20.
Y. Hirobe Y. Ashikawa R. Kawasaki K. Noda D. Akahoshi H. Kuwahara 《Solid State Communications》2006,137(4):191-195
The Hall resistivity and magnetization have been investigated in the ferromagnetic state of the bilayered manganite La2−2xSr1+2xMn2O7 (x=0.36). The Hall resistivity shows an increase in both the ordinary and anomalous Hall coefficients at low temperatures below 50 K, a region in which experimental evidence for the spin glass state has been found in a low magnetic field of 1 mT. The origin of the anomalous behavior of the Hall resistivity relevant to magnetic states may lie in the intrinsic microscopic inhomogeneity in a quasi-two-dimensional electron system. 相似文献