共查询到20条相似文献,搜索用时 15 毫秒
1.
Co3V 2O8 is a spin- 3/2 system on a Kagomé staircase and is known to undergo two magnetic phase transitions between 6 and 11 K. The H-T phase diagram of Co3V 2O8 derived by magnetization measurements on a single crystal is presented. Additionally both ordered magnetic structures were investigated by neutron powder diffraction experiments and solved using Bertaut’s macroscopic theory. For the ferromagnetic phase the magnetic moments of the Co2+ ions were found to be 1.5(3)μB and 2.7(1)μB at 3.5 K along the crystallographic a axis for the (4a) and (8e) sites, respectively. The antiferromagnetic phase exhibits a magnetic cell with a doubled b axis with respect to the nuclear one. The magnetic moments point along the a axis being 1.8(2)μB (4a) and 1.8(1)μB (8e) at 8 K. 相似文献
2.
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
3.
R. Masrour M. Hamedoun A. Benyoussef 《Journal of magnetism and magnetic materials》2010,322(3):301-304
The exchange interactions and the magnetic exchange energies are calculated by using the mean field theory and the probability law of Zn1−xMnxCr2O4 nanoparticles. The high-temperature series expansions have been applied in the spinels Zn1−xMnxCr2O4 systems, combined with the Padé approximants method, to determine the magnetic phase diagram, i.e. TC versus dilution x. The critical exponent associated with the magnetic susceptibility (γ) is deduced. The obtained value of γ is insensitive to the dilution ratio x and may be compared with other theoretical results based on the 3D Heisenberg model. 相似文献
4.
A structural and thermodynamic study of the newly synthesized single crystal Sr5Rh4O12 is reported. Sr5Rh4O12 consists of a triangular lattice of spin chains running along the c-axis. It is antiferromagnetically ordered below 23 K with the intrachain and interchain coupling being ferromagnetic (FM) and antiferromagnetic (AFM), respectively. There is strong evidence for an Ising character in the interaction and geometrical frustration that causes incomplete long-range AFM order. The isothermal magnetization exhibits two step-like transitions leading to a ferrimagnetic state at 2.4 T and a FM state at 4.8 T, respectively. Sr5Rh4O12 is a unique frustrated spin-chain system ever found in 4d and 5d based materials without a presence of an incomplete 3d-electron shell. 相似文献
5.
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 (χ⊥−χ∥) 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
6.
The paramagnetic susceptibility measured on La1−xYxSr2−yCay Mn2O7 (x, y or z=0, 0.03 and 0.1) manganites does not obey the Curie-Weiss law. The Curie constant exceeds the expected values by more than order of magnitude. Based on strong disorder we have compared the experimental data with predictions based on Griffith's singularity model. We find that this model allows for consistent interpretation of the data in contrary to a model assumes that magnetic polarons make contribution akin to cluster to susceptibility. In particular the values of Curie constant agree excellently with those theoretically expected, whereas the magnetic polarons model is less satisfactory. 相似文献
7.
Measurements of susceptibility, electron paramagnetic resonance and resistivity for La2/3Ca1/3MnO3 reveal a common temperature range between ∼266 and ∼300 K, where unusual aspects of physical properties are observed. The experimental results are discussed from the Griffiths theory that predicts the formation of ferromagnetic clusters before the Curie temperature is reached. It is emphasized that this theory incorporating the double-exchange mechanism could provide a good physical basis for the understanding of unusual transport properties. 相似文献
8.
Ren-fu Yang Young SunNai-li Di Qing-an LiZhao-hua Cheng 《Journal of magnetism and magnetic materials》2007
We have studied the magnetocaloric effect (MCE) in a bilayered La4/3Sr5/3Mn2O7 single crystal with applied field along both ab-plane and c-direction. Due to the quasi-two-dimensional structure, the crystal exhibits a strong anisotropy in the MCE. The difference of magnetic entropy change between two crystallographic directions depends on external magnetic fields and has a maximum of 2 J/kg K. A large low-field magnetic entropy change, reaching 3.2 J/kg K for a magnetic field change of 15 kOe, is observed when the applied field is along ab-plane. This large low-field magnetic entropy change is attributed to the rapid change of magnetization in response to external magnetic fields in the easy magnetizing plane. 相似文献
9.
Yuri V. Sushko Bruno DeHarak Gang Cao G. Shaw D.K. Powell J.W. Brill 《Solid State Communications》2004,130(5):341-346
Hydrostatic pressure effects on the temperature- and magnetic field dependencies of the in-plane and out-of-plane magnetization of the bi-layered perovskite Sr3Ru2O7 have been studied by SQUID magnetometer measurements under a hydrostatic helium-gas pressure. The anomalously enhanced low-temperature value of the paramagnetic susceptibility has been found to systematically decrease with increasing pressure. The effect is accompanied by an increase of the temperature Tmax of a pronounced peak of susceptibility. Thus, magnetization measurements under hydrostatic pressure reveal that the lattice contraction in the structure of Sr3Ru2O7 promotes antiferromagnetism and not ferromagnetism. The effects can be explained by the enhancement of the inter-bi-layer antiferromagnetic spin coupling, driven by the shortening of the superexchange path, and suppression, due to the band-broadening effect, of competing itinerant ferromagnetic correlations. 相似文献
10.
Jian-Jun Li 《Solid State Communications》2004,131(8):519-522
The magnetic nanoparticles of Mn1−xCuxFe2O4 (x=0, 0.2) were prepared by using a sol-gel method. It is proved that both the MnFe2O4 and Mn0.8Cu0.2Fe2O4 nanoparticle samples have superparamagnetic feature. Although the particle sizes are the same, substitution of a small fraction Cu for Mn results in the increase of magnetocrystallite anisotropy energy, thus enhances the blocking temperature from 130 K for MnFe2O4 to 260 K for Mn0.8Cu0.2Fe2O4. Mössbauer spectroscopy confirms that the anisotropy constant K of the Mn0.8Cu0.2Fe2O4 material is distinctly higher than that of the MnFe2O4 compound. Increase of the blocking temperature suggests that the approach we employed is effective to tackle the ‘superparamagnetic limit’ problem. 相似文献
11.
The magnetic properties of spinel FeCr2S4 single crystals were investigated by ferromagnetic resonance (FMR). The FMR spectrum displays a single absorption line in the whole temperature range measured for both H∥(111) and H⊥(111). With decreasing temperature, the line with H∥(111) shifts to lower fields, while that with H⊥(111) shifts to higher fields. By superposing all the FMR spectra measured in different directions at 110 K, a double-peak is obtained, which clarifies the origin of the FMR double-peak in polycrystalline sample. By taking account of magnetic anisotropy and demagnetizing effect, the orientation dependence of resonance field is well fitted. It is found that the magnetic anisotropy strengthens with decreasing temperature; however, it has no evident influence on transport and colossal magnetoresistance behavior. 相似文献
12.
Y. Hirobe Y. Kubo K. Kouyama H. Kunugita K. Ema H. Kuwahara 《Solid State Communications》2005,133(7):449-453
Photoinduced effects in a single crystal of bilayered manganites, La2−2xSr1+2xMn2O7 (x=0.38), were investigated in a wide range of temperatures by pump-probe measurement at a photon energy of 1.6 eV. In a ferromagnetic metallic state, significant enhancement of positive rise in differential reflectivity with a slow relaxing time of 100 ps was observed just below TC=127 K, indicating that the reflectivity change with the slow relaxation time constant is induced by laser heating. We have also observed an unconventional fast relaxing component that has a time constant of the order of 10 ps. This fast relaxing component, whose absolute value has an asymmetric peak at TC, is presumably due to short-range correlation of Jahn-Teller distortion. 相似文献
13.
The effect of transition element doping on the electronic and magnetic properties of La1.4Sr1.6Mn2O7
G.Q. Yu 《Solid State Communications》2007,141(3):136-140
The effect of transition element (TE=Cr, Fe, Co, Ni, Cu, Zn) doping on the electronic transport and magnetic properties in the bilayer manganite La1.4Sr1.6Mn2O7 is studied for the same dopant concentration fixed at 2%. Doping does not cause change in structure but different behavior in magnetic and transport properties. Except for Cr, all the other dopings significantly shift the magnetic transition temperature (TC) to a lower temperature. Associated with such a decrease, the insulator-metal transition temperature (TIM) decreases and the peak resistivity (ρp) at TIM increases. Cr doping enhances TC and TIM as well as decreases ρp. Fe doping apparently has a stronger effect than Co and Ni doping. It is also indicated that Cu doping causes an anomalously large increase in ρp. These behaviors are compared with those observed in other bilayer manganites such as La1.2Sr1.8Mn2O7 as well as in La0.7Ca0.3Mn1−xTExO3. 相似文献
14.
W.D. Hutchison D.J. Goossens K. Nishimura K. Mori Y. Isikawa A.J. Studer 《Journal of magnetism and magnetic materials》2006
Magnetisation and specific heat measurements, in the range 2 K to room temperature, demonstrate that three magnetic phases exist for the intermetallic compound TbNiAl4. Powder neutron diffraction, also carried out over a wide temperature range, establishes that the intermediate magnetic phase is incommensurate, and confirms that the lowest temperature phase has a linear antiferromagnetic structure with a (0 1 0) propagation vector. The respective transition (Néel) temperatures, in zero applied magnetic field are 34.0 and 28.0 K. 相似文献
15.
Takeshi Murata Tomoyuki TeraiTakashi Fukuda Tomoyuki Kakeshita 《Journal of magnetism and magnetic materials》2006
We have examined magnetizations as a function of temperature and magnetic field in layered perovskite manganites La2−2xSr1+2xMn2O7 single crystals (x=0.313, 0.315, 0.318, 0.320 and 0.350) in order to determine the phase boundary between two ferromagnets (one is an uniaxial ferromagnet whose easy axis is parallel to the c-axis and the other is a planar ferromagnet whose easy axis is within the ab-plane) and following results are obtained: (i) all the present manganites exhibit magnetic transitions from a ferromagnet to a paramagnet at 76, 107, 116, 120 and 125 K for x=0.313, 0.315, 0.318, 0.320 and 0.350, respectively; (ii) for x=0.318, 0.320 and 0.350, the magnetic structure is a planar ferromagnet below Curie temperature; (iii) for x=0.313 and 0.315, the magnetic structure changes from an uniaxial to a planar ferromagnet at 66 and 85 K, respectively. From the results described above we have constructed the magnetic phase diagram of layered perovskite manganite La2−2xSr1+2xMn2O7 (0.313?x?0.350). 相似文献
16.
The evolution of magnetic and electrical phases in La0.8−δCa0.2MnO3 was investigated in terms of La deficiency. We found that the increase of the La deficiency tends to raise the Curie temperature (TC) in La0.8−δCa0.2MnO3. The FM clusters formed in compounds with large La deficiency provide percolation paths above TC. With increasing the La defect, the transport property changes from insulating to metallic state, which is in association with the crossover from a second order to a first order magnetic phase transition in the vicinity of TC. 相似文献
17.
H. Gamari-Seale I.O. Troyanchuk K.L. Stefanopoulos 《Physica B: Condensed Matter》2008,403(17):2924-2929
In this paper we report the study of the perovskites La0.7Ca0.3Mn0.5Co0.5O3 and La0.8Sr0.2Mn0.5Co0.5O3 by neutron powder diffraction at various temperatures and magnetization measurements in zero applied field and at low cooling regimes. The replacement of half Mn by Co in La0.7Ca0.3MnO3 and La0.8Sr0.2MnO3 destroys their long-range ferromagnetism exhibiting a cluster glass ferromagnetic order similar to the one observed in many cobaltites. 相似文献
18.
E. Loudghiri A. Belayachi M. Nogues M. Taibi M.M. Cruz M. Godinho 《Journal of magnetism and magnetic materials》2008
In attempt to characterise the magnetic ordering in the whole composition range of the Cd1−xZnxCr2Se4 system, various magnetic measurements were performed on both crystalline and polycrystalline samples with 0?x?1. The magnetic properties of the system are typical of a ferromagnet below x=0.4 and of a complex antiferromagnet one above x=0.6. In this work the intermediate region was carefully studied. The variations of both M(T) and χac at low fields suggest that transitions from ferromagnetic to Gabay–Toulouse ferromagnetic-spin-glass mixed phase at low temperature occur in the range 0.41?x?0.58. The high-temperature susceptibility measurements show that for the whole concentration range the system obeys Curie–Weiss laws. The results can be explained by the coexistence of competing interactions (ferromagnetic between nearest neighbours and antiferromagnetic between higher order neighbours) and disorder due to the random substitution between zinc and cadmium ions in the tetrahedral sites of the spinel lattice. An experimental magnetic phase diagram of the system is established. 相似文献
19.
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
20.
Polycrystalline Sm1.4Sr1.2Ca0.4Mn2O7 has been successfully synthesized and investigated with respect to its magnetic and electrical properties. It is found that the sample shows a metal insulator (M-I) transition at 88 K. The maxima of the magnetoresistance (MR) ratio are 95.38% and 98.55% under applied fields of 2 T and 5 T, respectively. At 10 K, the MR attains ∼75% at 5 T. The large MR at low temperature can be attributed to the effects of nearly fully spin-polarized carriers tunneling through the insulating (Sm, Sr, Ca)2O2 layers between the adjacent MnO2 bi-layers. The magnetization data indicates the existence of ferromagnetic clusters. 相似文献