共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
A series of Ga doping perovskite cobaltite La2/3Sr1/3 (Co1-y Gay)03 (y = 0, 0.1, 0.2, 0.3 and 0.4) are prepared by the standard solid-state reaction method. Their magnetic properties and Co ions spin state transitions are studied. Upon doping, no appreciable structure changes can be found. However, the corresponding Curie temperature sharply decreases and the magnetization is greatly reduced, indicating that Ga doping destroys the ferromagnetic interaction in the system. In addition, the high temperature magnetization data follow the Curie-Weiss law. At least one kind of Co ions (Co^3+ or Co^4+) favours the mixed spin state, and most Co ions are at the lower spin state (low and intermediate state). With increasing Ga content, more Co ions transit to the higher spin state. 相似文献
3.
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
4.
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
5.
C. Martin M. Miclau M. Giot A. Maignan F. Bouree-Vigneron 《Journal of magnetism and magnetic materials》2009,321(23):3938-3944
CaMn0.96Mo0.04O3 is an example of Mn4+ rich perovskite manganites, which exhibits a net ferromagnetic component at low temperature, observed by dc magnetization and ac susceptibility. To characterize the magnetic state of this compound, neutron powder diffraction was carried out in the 2-400 K temperature range, showing that it is necessary to use three components (ferromagnetic and G- and A-type antiferromagnetic) to describe it. This particular state is in agreement with the unusual magnetic behaviour observed by macroscopic measurements and is compared to the one observed for manganites with similar Mn valence but obtained by A-site substitution. 相似文献
6.
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
7.
The role of vibrational anisotropy of Mn3+O6 octahedron in the phase separation behavior of La0.67−yPryCa0.33MnO3 (x=0, 0.15, 0.25 and 0.30) has been investigated by means of magnetization M, internal friction Q−1, Young's modulus E along with the X-ray powder diffraction measurements. For the samples with y=0 and 0.15, the Q−1 exhibits three peaks in the ferromagnetic region, which are attributed to the intrinsic inhomogeneity of ferromagnetic phase, i.e. the electronic phase separation with the coexistence of insulating and conducting phases. However, both the samples with y=0.25 and 0.30 undergo a magnetic phase separation with the coexistence of the antiferromagnetic and ferromagnetic phases, and the Q−1 peaks related to the electronic phase separation have not been observed. In addition, the Q−1 exhibits a peak in the paramagnetic region for all samples, which may result from the formation of magnetic clusters. We observed that the evolution from electronic to magnetic phase separation is close related to the rapid increase in the ratio of two kinds of Jahn-Teller distortion modes Q3 and Q2, i.e. Q3/Q2. A schematic phase diagram is given in the text, and it is suggested that the enhancement of vibrational anisotropy of Mn3+O6 octahedron plays a key role in the evolution from electronic to magnetic phase separation. 相似文献
8.
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
9.
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
10.
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
11.
Moshe Kuznietz Tomoo YamamuraDexin Li Yoshinobu Shiokawa 《Journal of magnetism and magnetic materials》2008
Rather old preparation of the compounds ThCo2Ge2 and ThCo2Si2 and their magnetic study in the temperature range 100–570 K, published by Omejec and Ban [Z. Anorg. Allg. Chem. 380 (1971) 111], indicated that both compounds ordered ferrromagnetically below 100 K. In order to verify the old data, polycrystalline samples of ThCo2Ge2 and ThCo2Si2 have been prepared by arc melting and subsequent annealing, and studied by X-ray diffraction at room temperature (RT), by superconducting quantum interference device (SQUID)-magnetization and AC-susceptibility measurements at 2–320 K, and by dc-magnetization measurements in variable magnetic fields up to 120 kOe at 5, 80, and 283 K. The magnetic measurements confirm the ferromagnetic ordering in both compounds, but with totally different Curie temperatures: ≈120(20) K for ThCo2Ge2 and above 320 K for ThCo2Si2. The paramagnetic values of ThCo2Ge2 and the ordering of both compounds are discussed and compared with the old results of Omejec and Ban. 相似文献
12.
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
13.
O. Volkova K. Klimov O. Savelieva N. Tristan E. Goodilin B. Buechner A. Vasiliev 《Journal of magnetism and magnetic materials》2006
Magnetic and transport properties of double distorted perovskites CaCuMn6O12 and CaCu2Mn5O12 are studied in a range 2–300 K. The leading role in magnetism of these compounds belongs to antiferromagnetic exchange interaction of Cu2+ in square coordination with Mn3+/Mn4+ in octahedral coordination. The values of saturation magnetization indicate that Mn3+ ions in square coordination are coupled ferromagnetically with Mn3+/Mn4+ in octahedral coordination. The colossal magnetoresistance in the pellet samples is due assumingly to intergranular spin-polarized tunneling of current carriers. 相似文献
14.
Tb2O2SO4 orders antiferromagnetically at 3.9 K in a four-sublattice structure with two of the nearest-neighbour moments antiparallel and two almost perpendicular to that of a central ion. Specific-heat and magnetization measurements were carried out and allowed to establish the phase diagram for the external magnetic field along one of the moments' direction. Starting at the Néel temperature, the boundary of the paramagnetic phase is first shifted to lower temperatures for increasing field and then it stays at constant temperature for further increase of field. The shift is caused by the reduction of the staggered field that is existing in the antiferromagnetic phase. The experimental results are corroberated to a large extent by mean-field calculations. 相似文献
15.
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
16.
P. Schobinger-Papamantellos J. Rodríguez-Carvajal 《Journal of magnetism and magnetic materials》2010,322(1):119-132
The temperature magnetic phase diagrams, of the dimorphic DySi compound, have been studied in terms of wave vectors in the range 1.5-45 K, by neutron diffraction. The polycrystalline sample consists of 26% of CrB-type (Cmcm no. 63, all atoms at 4c site: (0, y, 1/4)) and of 74% of FeB-type (Pnma no. 62, all atoms at 4c site: (x, 1/4, z)). The CrB-ordering is described by the wave vector: q1=(0, 0, 1/2) over the entire magnetically ordered regime with a uniaxial magnetic structure along the shortest axis c. The FeB-type magnetic phase diagram reveals three distinct regions of magnetic ordering below TN and one first order transition at T2=23.5 K (on heating). The ordering is described by two symmetry independent magnetic vectors q2=(0, 1/2, 1/6) and q3=(0, q3y, q3z) with a temperature variable length. At 1.5 K q3y≈1/2 and q3z≈1/11. The two phases coexist in the form of domains. They differ in the moment orientation of the q3 phase that deviates by ∼22° from the b-axis in the (0, 0, 1) plane. The low temperature range (LT) 1.5 K—T2 subdivides into two regions: (i) LT-1, between 1.5 K—T1 where the relative amount of the two phases remains unchanged and in (ii) LT-2: T1-T2 where the amount of the incommensurate q3 phase increases at the cost of the commensurate q2 amplitude modulated structure which remains unchanged but fully disappears at the first order transition at T2=23.5 K. The q3 phase undergoes minor changes until 22 K and gets destabilised at T2 where the q3z component jumps from the LT value q3z≈1/11 to the HT value ≈1/7 and the q3y component increases from 0.484(1) to 0.495(1). (iii) The high temperature (HT) range T2-TN (TN=40±1 K) is described by a single wave vector q3. The disproportionation of the HT magnetic phase q3 below T2 into two coexisting distinct phases q2, q3 down to 1.5 K is an unusual phenomenon, to our knowledge observed for the first time. Various mechanisms are discussed. 相似文献
17.
Strain in the La0.67Ca0.33MnO3 films has been tuned by varying substrate and film thickness, and its effects on magnetic anisotropy are studied based on the measurements of isothermal magnetization. Measuring the strain in the films by the out-of-plane lattice parameter (c), we found a strong dependence of the magnetic anisotropy constant (Ku) on strain. Ku decreases linearly from ∼−1.1×106 erg/cm3 for c=0.763 nm to 1.2×106 erg/cm3 for c=0.776 nm, corresponding to a change from tensile strain to compressive strain. Positive Ku signifies a uniaxial anisotropy with the easy axis perpendicular to the film plane, while negative Ku demonstrates an anisotropy of the easy plane character. Smaller or larger c leads a decrease or increase in Ku, which indicates the presence of other effects in addition to those associated with strain. Three distinctive processes for the magnetization are observed along the hard magnetic axis of the films on (001)SrTiO3, suggesting a possibility of strain relaxation even in ultra-thin films. 相似文献
18.
A field-induced magnetic transition is observed in quasi-one-dimensional spin system PbCo2V 2O8 by means of magnetic and heat capacity measurements. Our experimental results clearly show that an antiferromagnetic-paramagnetic transition occurs in PbCo2V 2O8, when a magnetic field larger than 4 T is applied. Such a field-induced magnetic transition is quite similar to that observed in isostructural BaCo2V 2O8 or SrCo2V 2O8. Therefore, we suggest that this may be a universal feature in quasi-one-dimensional spin-3 /2 (Co2+) chain systems, ACo2V 2O8. 相似文献
19.
The paper presents the results of an experimental study of thermal expansion of isostructural orthorhombic ErFeO3 and ErAlO3 single crystals. Changes of lattice parameters have been investigated by X-ray measurements in the 10-300 K temperature range. Above ∼150 K, experimental results correspond well to the phonon mechanism. At low temperatures distinct anisotropic anomalies were observed in both compounds; and a correlation with the magnetic properties of the relevant ions is noted. 相似文献
20.
M. Belmeguenai F. Zighem Y. Roussigné K. Westerholt 《Journal of magnetism and magnetic materials》2009,321(7):750-753
Co2MnGe films of 30 and 50 nm in thickness were grown by RF-sputtering. Their magnetic anisotropies, dynamic properties and the different excited spin wave modes have been studied using conventional ferromagnetic resonance (FMR) and Microstrip line FMR (MS-FMR). From the in-plane and the out-of-plane resonance field values, the effective magnetization (4πMeff) and the g-factor are deduced. These values are then used to fit the in-plane angular-dependence of the uniform precession mode and the field-dependence of the resonance frequency of the uniform mode and the first perpendicular standing spin wave to determine the in-plane uniaxial, the four-fold anisotropy fields, the exchange stiffness constant and the magnetization at saturation. The samples exhibit a clear predominant four-fold magnetic anisotropy besides a smaller uniaxial anisotropy. This uniaxial anisotropy is most probably induced by the growth conditions. 相似文献