共查询到20条相似文献,搜索用时 15 毫秒
1.
R. Zinke J. Schulenburg J. Richter 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):147-152
We investigate the ground-state magnetic long-range order of
quasi-one-dimensional quantum Heisenberg antiferromagnets for spin
quantum numbers s = 1/2 and s = 1. We use the coupled
cluster method to calculate the sublattice magnetization and
its dependence on the inter-chain coupling J⊥.
We find that for the unfrustrated spin-1/2 system,
an infinitesimal inter-chain coupling is sufficient to stabilize
magnetic long-range order, in agreement with results obtained
by other methods.
For s = 1, we find that a finite inter-chain coupling
is necessary to stabilize magnetic long-range order.
Furthermore, we consider a quasi one-dimensional spin-1/2 system,
where a frustrating next-nearest neighbor in-chain coupling is included.
We find that for stronger frustration as well, a finite inter-chain coupling
is necessary to have magnetic long-range order in the ground state, and that the strength of the inter-chain coupling necessary
to establish magnetic long-range order is related to the size of the spin gap of the isolated chain. 相似文献
2.
S Sundar Manoharan Ranjan K SahuD Elefant C.M Schneider 《Solid State Communications》2003,125(2):103-106
We observe a sharp increase in negative magneto-resistance ratio up to 40% for x=0.1, in La0.5Sr0.5Co1−xRuxO3 which is due to the magnetic disorder induced by an anti-ferromagnetic interaction between Co and Ru ions. We also observe a metal to insulator and a ferromagnetic to anti-ferromagnetic transition for 0≤x≤0.3. Ruthenium (IV) ion disrupts an intermediate spin state of cobalt (Co3+:t2g5eg1), forcing a double exchange mediated ferromagnetic state to an anti-ferromagnetic spin state for x≥0.2. 相似文献
3.
Visible photoluminescence and its temperature dependence of La2/3Ca1/3MnO3 in the temperature range 138-293 K were measured. It was observed that the main broad band centered at ∼1.77 eV with the shoulders at ∼1.57 and ∼1.90 eV existed in the entire temperature range. It can be well fitted by three Gaussian curves B1, B2 and B3 centered at ∼1.52, ∼1.75 and ∼1.92 eV, respectively. The intensities of the peak B1 and B2 vary as temperature increases. In the entire temperature range, the intensity of B1 increases with increasing temperature, whereas that of B2 decreases. The photoluminescence mechanisms for La2/3Ca1/3MnO3 are presented based on the electronic structures formed by the interactions among spin, charge and lattice, in which B1 was identified with the charge transfer excitation of an electron from the lower Jahn-Teller split eg level of a Mn3+ ion to the eg level of an adjacent Mn4+ ion, B2 is assigned to the transition between the spin up and spin down eg bands separated by Hund's coupling energy EJ and B3 is attributed to the transition, determined by the crystal field energy EC, between a t2g core electron of Mn3+ to the spin up eg bands of Mn4+ by a dipole allowed charge transfer process. 相似文献
4.
Wei Ning 《Journal of magnetism and magnetic materials》2009,321(2):88-90
Electron spin resonance (ESR) measurements have been performed on polycrystalline samples of Pr1−xCaxMnO3 (x=0.4, 0.5) in the temperature range of 100-300 K. The temperature dependence of ESR intensity, g value and linewidth shows the existence of ferromagnetic spin correlations in the paramagnetic state. With decreasing temperature, the ferromagnetic spin correlations switch to antiferromagnetic spin correlations in the charge ordering state and vanish at the antiferromagnetic ordering temperature TN. 相似文献
5.
Raman scattering on single crystals of Eu3S4 does not show the allowed q=o phonon modes in the cubic phase and exhibits no new modes in the distorted low temperature phase (T<186 K). Above the Curie temperature Tc=3.8 K the scattering is dominated by a spin-disorder induced one-phonon density of states allowing for the observation of the zone boundary phonon breathing mode of the S2?ions. This mode does not show any anomaly near the charge order -disorder phase transition Tt=186 K. Temperature tunable spin fluctuations associated with the temperature activated Eu2+→Eu3+ electron hopping are detected in the scattering intensity, superimposed on the usual thermal spin disorder. 相似文献
6.
We report an angle-resolved photoemission spectroscopy study of electronic structures of Eu1−xLaxFe2As2 single crystals, in which the spin density wave transition is suppressed with La doping. In the paramagnetic state, the Fermi surface maps are similar for all dopings, with chemical potential shifts corresponding to the extra electrons introduced by the La doping. In the spin density wave state, we identify electronic structure signatures that relate to the spin density wave transition. Bands around M show that the energy of the system is saved by the band shifts towards high energies, and the shifts decrease with increasing doping, in agreement with the weakened magnetic order. 相似文献
7.
Antiferromagnetic phase transition in two vanadium garnets AgCa2Co2V3O12 and AgCa2Ni2V3O12 has been found and investigated extensively. The heat capacity exhibits sharp peak due to the antiferromagnetic order with the Néel temperature TN=6.39 K for AgCa2Co2V3O12 and 7.21 K for AgCa2Ni2V3O12, respectively. The magnetic susceptibilities exhibit broad maximum, and these TN correspond to the inflection points of the magnetic susceptibility χ a little lower than T(χmax). The magnetic entropy changes from zero to 20 K per mol Co2+ and Ni2+ ions are 5.31 J K−1 mol-Co2+-ion−1 and 6.85 J K−1 mol-Ni2+-ion−1, indicating S=1/2 for Co2+ ion and S=1 for Ni2+ ion. The magnetic susceptibility of AgCa2Ni2V3O12 shows the Curie-Weiss behavior between 20 and 350 K with the effective magnetic moment μeff=3.23 μB Ni2+-ion−1 and the Weiss constant θ=−16.4 K (antiferromagnetic sign). Nevertheless, the simple Curie-Weiss law cannot be applicable for AgCa2Co2V3O12. The complex temperature dependence of magnetic susceptibility has been interpreted within the framework of Tanabe-Sugano energy diagram, which is analyzed on the basis of crystalline electric field. The ground state is the spin doublet state 2E(t26e) and the first excited state is spin quartet state 4T1(t25e2) which locates extremely close to the ground state. The low spin state S=1/2 for Co2+ ion is verified experimentally at least below 20 K which is in agreement with the result of the heat capacity. 相似文献
8.
The electron spin resonance of the minority defect Fe4+-V0 has been observed in SrTiO3. It is the first pair center identified with a two-fold positive charge with respect to the lattice. For Fe4+ it occurs in the unusual high spin S = 2 state. Optically-induced conversion to the neighbor Fe3+-V0 charge state served to identify the acceptor transfer bands, showing the potentiality of the conversion-rate method. 相似文献
9.
The exact solution for the evolution of nuclear spin polarizations in a system with spin-spin coupling constant g identical for all spin pairs is obtained on the condition that only one (first) spin is polarized at zero time. It is shown that the polarization P 1(t) of the first spin has the form of periodic time pulsations with the period 4π/g. In every period, the function P 1(t) changes from its initial value P(0)=1 to 1/3 during the time on the order of t≈4π/Ng, if the number of spins N?1, and remains in the state P 1(t)=1/3 virtually during the entire period. A simple classical model within the framework of mean-field theory explains the physical nature of the nonergodic dynamics of the system. 相似文献
10.
The magnetic properties of polycrystalline PrFe1−xNixO3 (x≤0.3) system were studied using Mössbauer spectroscopy and magnetization measurements. The Mossbauer spectra exhibit six line spectra which loses its sharpness as the Ni substitution increases within the system. As the Ni concentration in the system increases, the hyperfine field and isomer shift shows decrease, which is vivid from the sluggish nature of the sextets. The small value of quadrupole splitting confirms the octahedral environment of the Fe+3 ions. The magnetization curves show the reversible behavior and represent the fall in negative molecular field leading to AFM frustration. From these results, we conclude that sagging in the spectra reveals the change from antiferromagnetic state to ferromagnetic state, which can be attributed to mixed state of Fe+3 ions i.e. high spin (HS) and low spin (LS) which is a consequence of progressive collapse of Hund’s rule due to HS→LS transition. These results confirm the weak ferromagnetic component due to canted-AFM spin arrangement of Fe3+ magnetic moments. 相似文献
11.
M. Hagiwara T. Shima R. Kitada H. Deguchi K. Koyama 《Physica C: Superconductivity and its Applications》2010,470(20):1052-1055
Intergrain ordering phenomena of frustrated ceramic YBa2Cu4O8 (Y124) and dual phase mixed ceramic containing CuO are studied by both magnetic and resistivity observations. Magnetically estimated intergrain ordering temperature Tc2 and zero-resistivity attainment temperature Tz are both decreased with CuO content. However, it is also revealed that mutual location of Tc2 and Tz is changed. For the mixed ceramic with torn intergrain network structure, Tz stays above Tc2, indicating local dissolution of frustration by cluster structure. On the other side, remaining resistivity tails blow Tc2, indicating intrinsic fluctuation effect on the resistivity caused by frustration in the ordered state. It is known then that, superconductive ceramic samples which is free from structural phase inhomogeneity is essential in order to clarify the frustration effect. 相似文献
12.
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
13.
Y Furukawa S TakadaK Kumagai T KawashimaE Takayama-Muromachi N KobayashiT Fukase K ChibaT Goto 《Journal of Physics and Chemistry of Solids》2002,63(12):2315-2318
We have carried out 99/101Ru and 63/65Cu nuclear magnetic resonance experiments in order to investigate magnetic and electronic properties of the magnetic superconductor RuSr2RECu2O8 (RE=Gd, Eu and Y). The two kinds of 99/101Ru signals were observed in the magnetically ordered state for each system, suggesting a charge segregation of Ru5+ (S=3/2) and Ru4+ (S=1) ions in the RuO2 layers. The internal field at the Cu sites is revealed to be of the order of kilo Oe, indicating weak magnetic interactions between the CuO2 and RuO2 planes. The temperature dependence of nuclear spin-lattice relaxation time T1 of 63Cu in RE=Y shows a ‘spin gap’ like behavior, suggesting the system is under-doped. 相似文献
14.
We study the effect of dimerization of TMTSF molecules and the effect of magnetic field (Zeeman splitting) on the phase competition in quasi one-dimensional organic superconductors (TMTSF)2X by applying the random phase approximation method. As for the dimerization effect, we conclude that due to the decrease of the dimerization, which corresponds to applying the pressure and cooling, spin and charge density wave states are suppressed and give way to a superconducting state. As for the magnetic field effect, we find generally that spin-triplet pairing mediated by a coexistence of 2kF spin and 2kF charge fluctuations can be strongly enhanced by applying magnetic field rather than triplet pairing due to a ferromagnetic spin fluctuations. Applying the above idea to (TMTSF)2X compounds, a magnetic field induced singlet-triplet transition is consistent with above mechanism in (TMTSF)2ClO4. 相似文献
15.
Systematic studies of X-ray, magnetic, electronic transport, and elastic properties have been performed on polycrystalline Bi0.5Ca0.4Sr0.1MnO3 sample. The sample exhibits charge ordering (CO) state below TCO (=304 K), accompanied by a distinct maximum in magnetization. The softening of Young's modulus in the vicinity of TCO indicates that there is a strong coupling of electron-phonon due to Jahn-Teller (JT) effect. The dynamic ferromagnetic spin correlations are observed at high temperatures above TCO, which are replaced by antiferromagnetic (AFM) spin fluctuations at a concomitant CO transition. Below 32 K, a spin-glass (SG) state dominates at low temperatures. The voltage-current (V-I) characteristics measurement results indicate that the non-linear conduction starts above a threshold current, giving rise to a region of negative differential resistance (NDR). The origin of the non-linear conduction is discussed in view of current induced collapse of CO state associated with phase-separation mechanism. 相似文献
16.
We have studied the magnetic and transport properties of Fe doped La0.65A0.35Mn0.95Fe0.05O3 (A = Ca, Sr, Pb, Ba) manganites. All the compositions show ferromagnetic/metal to paramagnetic/insulator transition (TC) except the Pb doped sample which is insulating and ferromagnetic (FM) in the entire temperature range. The magnetization and TC are decreased by decreasing the cation size on La site. The transition temperature and magnetic moment at 77 K is a maximum for Sr doped sample and is decreasing if we increase or decrease the cation size from Sr size. The maximum value of TC and magnetic moment for Sr based sample is most likely due to the closer ionic sizes of La and Sr as compared to the other dopants (Ca, Pb, and Ba). We observed a spin freezing type effect in the Pb doped sample below 120 K in resistivity, ac susceptibility and in magnetization. This suggests that the AFM interactions introduced by the Fe are most effective in the Pb doped composition leading to increased competition between the FM and AFM interactions. This FM and AFM interaction generates some degree of frustration leading to the appearance of spin glass like phase whose typical magnetic behavior is studied for small ion when the metallic like behavior is lost. 相似文献
17.
O17 nuclear magnetic resonance has been observed in metallic V2O3 with frequency shifts from (?0.10 ± 0.02)-(?0.05 ± 0.02) per cent between 170 and 460°K respectively, a linewidth of 37 ± 5 oe and spin-lattice relaxation rate 1/T1 ≈ 60 sec?1 at 296°K. From these quantities, covalency parameters fs/2S = ? 0.35 × 10?3 and ?π/2S ≈ ? 0.07 are calculated. One of the two vanadium 3d electrons in the antiferromagnetic state below the 170°K metal-insulator transition is inferred to lie in a non-magnetic state, while covalent charge transfer augments the spin moment of the other 3d electron to the observed 1.2 μB. 相似文献
18.
The structural and magnetic properties of ErMn2H4.6 have been studied by X-ray and neutron diffraction up to the pressures of 15 and 6 GPa, respectively. In the pressure range 0<P<3 GPa we observe a first-order phase transition to new high-pressure (HP) phase. The HP phase has the same hexagonal unit cell as the ambient-pressure phase but smaller lattice parameters (ΔV/V=−5%). The structural transition results in suppression of the long-range antiferromagnetic order. Our results suggest that pressure changes positions of the hydrogen atoms in the metal host. We speculate that the new arrangement of hydrogen atoms induces spin frustration and, therefore, suppresses long-range magnetic order in the HP phase. 相似文献
19.
The far-infrared spectrum of tetrahydrothiophene is reinvestigated with a resolution of 0.12 cm?1 in the region of 50–350 cm?1. In addition to the bend transitions (νb) below 120 cm?1 reported previously, a number of sequences revealed by the improved resolution are observed for the first time and assigned to transitions of 2νb, of the twist (νt), and of difference combinations (νt - νb). Simple one-dimensional modeling of the twist sequence, which is derived from a self-consistent bend-twist energy level diagram, with a quadratic-quartic Hamiltonian suggests a barrier to planarity on the order of 4250 cm?1. A two-dimensional potential function in the dimensionless coordinates is found to be V(qb, qt) = ?249.6qb2 + 4.48qb4 ? 215.5qt2 + 2.73qt4 + 7.00qb2qt2. 相似文献
20.
B. SamantarayS.K. Srivastava S. Ravi 《Journal of magnetism and magnetic materials》2011,323(21):2622-2626
The magnetic dynamics of charge ordered Nd0.8Na0.2MnO3 compound was studied by measuring the temperature variation of magnetization for different magnetic fields up to 7 T and, the field variation of magnetization at different temperatures down to 5 K. This sample exhibits a charge-ordering transition at 180 K, followed by a weak ferromagnetic (FM) transition at around 100 K and a spin glass like transition below 40 K. Suppression of charge-ordering and spin glass like transition and increase in FM TC were observed with an increase in magnetic field. A reversible metamagnetic transition above a threshold field (Hf) of 4.5 T was observed at 130 K, followed by a saturation magnetization of 3.2 μB/f.u. However at 5 K, an irreversible field induced first order phase transition from charge ordered state to FM state was observed at Hf=5 T. For comparison, the temperature and field variations of magnetization were studied on a FM compound from the same series with the composition Nd0.90Na0.10MnO3. A clear FM transition with a TC of 113 K and a saturation magnetization of 4.3 μB/f.u was observed. 相似文献