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1.
The electronic and magnetic properties of Cu-doped perovskite La0.7Ca0.3Mn1−xCuxO3 obtained by doping Cu on its Mn sites have been studied. The perovskite structure was found to remain intact up to the highest doping level of x=0.20. At low Cu concentration (x=0.05) the temperature-dependence of resistivity of the material exhibited up to two peaks corresponding to the magnetic transitions from the PM to the FM phase, and from the FM to the AFM phase. In general, the doping level was found to suppress the ferromagnetic ordering of the material, increase its resistivity, and produce large values of magnetoresistance near the resistivity peak. These results were explained as due to the formation of the antiferromagnetic phase. 相似文献
2.
We observed the giant magnetoimpedance and colossal ac magnetoresistance for a Cu coil wound on La0.67Sr0.33MnO3 under low dc magnetic fields. Even though the dc magnetoresistance for La0.67Sr0.33MnO3 plate is only −2.4% under H=12 kOe, a Cu coil wound on La0.67Sr0.33MnO3 plate exhibits a colossal ac magnetoresistance of −93% at 10 MHz and a giant magnetoimpedance of −59% in a wide frequency range of 500 kHz-10 MHz under a longitudinal field . The transverse magnetoimpedance is weaker than the longitudinal one. The giant magnetoimpedance and colossal ac magnetoresistance for a Cu coil wound on La0.67Sr0.33MnO3 are connected with the variation of permeability induced by dc magnetic field. 相似文献
3.
Guangtao Wang Minping Zhang Lihua Zheng Zongxian Yang 《Solid State Communications》2011,151(18):1231-1235
The electronic structure and magnetic properties of new layered oxyselenide compounds La2O3Fe2Se2 and La2O3Co2Se2 are studied by first-principles calculations. Our results indicate that both compounds are Mott-insulators with orbital ordering. The ground states of both compounds are the checkerboard antiferromagnetic states, which are different from the iron pnictide superconductors, although their structures are similar to those of the Fe-As-based superconductors. 相似文献
4.
V. A. Ryzhov A. V. Lazuta V. P. Khavronin I. I. Larionov I. O. Troaynchuk D. D. Khalyavin 《Solid State Communications》2004,130(12):803-808
The data on the resistance and magnetoresistance (MR) as well as measurements of the linear and nonlinear susceptibilities are presented for a Nd0.75Ba0.25MnO3 single crystal with the Curie temperature TC≈129 K. Although this compound remains insulating in the ferromagnetic state, its resistance has an anomaly near TC and it reveals the colossal magnetoresistance. The data on the magnetic response are well described by the dynamic scaling theory for 3D isotropic ferromagnets in the paramagnetic critical region at τ>τ*≈0.11, τ=(T−TC)/TC. Below τ* an anomalous critical behavior is found that suggests the coexistence of two magnetic phases. This behavior is discussed in terms of a phase separation which can occur in the moderately doped manganites exhibiting an orbital ordering. 相似文献
5.
Baris Emre Ilker Dincer Eyup Duman Yalcin Elerman 《Solid State Communications》2011,151(24):2004-2007
The thermal and magnetothermal properties of La0.5Pr0.5Mn2Si2 and isostructural LaFe2Si2 intermetallic compounds in the temperature range 4.5-303 K are reported with and without applied magnetic field. The electronic, lattice, and magnetic contributions to the heat capacity of La0.5Pr0.5Mn2Si2 are determined and analyzed. We have determined and from heat capacity experiments; the values are in line with those from the magnetization measurements. We conclude that in order to observe the anomaly in the heat capacity data around in the system, the transition around should occur in a narrow temperature interval. 相似文献
6.
The magnetic properties of the ferrimagnetic cobaltite CaBaCo4O7 are systematically investigated. We find that the susceptibility exhibits a downward deviation below ∼360 K, suggesting the occurrence of short-range magnetic correlations at a temperature well above TC. The effective moment is determined to be ., which is consistent with that expected for the Co2+/Co3+ high spin species. Using a criterion given by Banerjee [Phys. Lett. 12 (1964) 16], we demonstrate that the paramagnetic to ferrimagnetic transition in CaBaCo4O7 has a first order character. 相似文献
7.
J. Agostinho Moreira A. Almeida M.R. Chaves J.M. Machado da Silva S.M.F. Vilela 《Solid State Communications》2011,151(5):368-371
This work reports an experimental investigation of the ferroelectric character of magnetic phases of the orthorhombic Eu1−xY xMnO3 system at low temperatures. The temperature dependence of the polarization curves clearly reveals the existence of a re-entrant improper ferroelectric phase for x=0.2, 0.3 and 0.5. A ferroelectric phase is also stable for x=0.4, and we have no experimental evidence for its vanishing down to 7 K. From these and early results obtained using other experimental techniques, the corresponding (x,T) phase diagram was traced, yielding significant differences with regard to the ones previously reported. 相似文献
8.
The effects of spin structures on the Fermi surface topologies of BaFe2As2 were calculated using the first-principles approach. Here, we considered the nonmagnetic, Checkerboard, Stripe, and SDW (spin-density-wave) structures as well as a tetragonal structure labeled as STR17. By comparing the calculated results with the published angle-resolved photoemission spectroscopy from the literature, we propose that most of the experimentally observed Fermi surfaces of BaFe2As2 are the thermal mixture of those of the SDW, STR17, and Stripe structures. 相似文献
9.
The antiferromagnet GdAg2 has been shown to be a good model system for the magnetoelastic paradox (MEP), because it exhibits large symmetry conserving magnetoelastic strains and the antiferromagnetic propagation vector breaks the tetragonal lattice symmetry (therefore a large symmetry breaking magnetoelastic strain can be expected in a single magnetic structure). As in many similar Gd based compounds no symmetry breaking strain has been found in the experiment. In order to investigate this MEP further, we have measured magnetostriction and magnetization on a textured polycrystal. The behaviour closely resembles that of GdNi2B2C, the prototype system for the magnetoelastic paradox (MEP). Our forced magnetostriction data indicate that the crystal distorts in applied magnetic field and gives further evidence that the MEP is a low field effect. The observed phase transitions are in agreement with available specific heat and neutron diffraction data. Moreover, the saturation magnetic field was measured in high pulsed magnetic fields and agrees well with the value calculated from the Standard Model of Rare Earth Magnetism (SMREM). 相似文献
10.
M. Herak 《Solid State Communications》2011,151(21):1588-1592
A combination of highly sensitive torque magnetometry in low magnetic fields and a phenomenological approach to magnetic anisotropy is used to probe the symmetry of the antiferromagnetically ordered state of spin S=1/2 system Cu3TeO6. The results show that the ordered state has four antiferromagnetic domains with spin axis in the 〈1±1±1〉 directions, in agreement with the previously reported neutron measurements. These results show that this approach, previously applied to ferromagnets and highly anisotropic antiferromagnets, is also successful in determining the symmetry of weakly anisotropic Heisenberg antiferromagnets with multiple spin domains. Possible microscopic origin of magnetic anisotropy is briefly discussed. 相似文献
11.
The thermodynamic properties of the spinel ferromagnetic compounds CdCr2Se4 and CdCr2S4 have been investigated by making heat capacity and thermal expansion measurements on single crystals. For both compounds, the ferromagnetic transition is marked by λ-type thermal anomalies, and the results provide a pressure dependence of the transition temperatures that is in agreement with direct measurements. Below the transition, CdCr2S4 shows an anomalous heat-capacity contribution and negative thermal expansion, which are in contrast to the conventional behavior found in CdCr2Se4. 相似文献
12.
R. M’nassri W. Cheikhrouhou-Koubaa M. Koubaa N. Boudjada A. Cheikhrouhou 《Solid State Communications》2011,151(21):1579-1582
Studies of the structural, magnetic and magnetocaloric properties of polycrystalline Pr0.6−xEuxSr0.4MnO3 (0≤x≤0.15) perovskite manganites were carried out. Substitution for praseodymium with europium, with smaller ionic radius, induces local distortion in the 〈Mn–O–Mn〉 bonds and consequently causes a random distribution in the magnetic exchange interactions. The competition between magnetic interactions leads to the appearance of an inhomogeneous magnetic state in our samples. Pr0.6−xEuxSr0.4MnO3 (x=0, 0.05, 0.1 and 0.15) polycrystalline samples were prepared using the solid–solid reaction method at high temperature. The compounds yielded are single phase and crystallize in the orthorhombic system with the Pnma space group. The substitution of Eu for Pr leads to a decrease of the Curie temperature TC from 303 K for x=0.00 to 260 K for x=0.15. All of our compounds exhibit a large magnetic entropy change with a maximum around 2.2 J/kg K under a magnetic applied field change of 2 T for all compounds. 相似文献
13.
C. P. Yang Y. Z. Wang G. H. Wu B. P. Hu J. L. Wang Z. X. Wang Z. L. Jiang J. Zhu 《Solid State Communications》1999,110(12):667-671
A Y2Fe15Cr2 single crystal with the Th2Ni17-type structure has been prepared by the Czochralski method and investigated by means of Laue back-reflection, metallographic observation, X-ray diffraction, the singular point detection technique and magnetic measurements. A magnetohistory effect has been observed at a low temperature. Magnetization curves have been measured along the easy and hard directions in fields up to 6.5 T. The saturation magnetization and magnetocrystalline anisotropy field decrease with increasing temperature. The experimental magnetocrystalline anisotropy constant is in good agreement with the calculation results on first approximation. 相似文献
14.
The first principle method was applied to study the electronic structure and magnetic properties of the compound of Cu(HCO2)(NO3)(pyz). The density of states, the electronic structure and the spin magnetic moments are calculated. The results reveal that the compound has a ferromagnetic interaction arising from the bridging μ- HCO2− and pyz ligands, and the ferromagnetic properties come from the spin delocalization effect. The spin magnetic moment per molecule mainly comes from the Cu ion, but has little contribution from O, N and C anion. 相似文献
15.
We report on the enhanced electromechanical, magnetic and magnetoelectric properties of Bi1−xCaxFe1−xTixO3 solid solutions. The crystal structure of the x≈0.25 compounds are close to the rhombohedral-orthorhombic phase boundary, and the solid solutions are characterized by increased electromechanical properties due to the polarization extension near the polar-nonpolar border. The homogenous weakly ferromagnetic state is established at x>0.15 doping. The chemical doping shifts the magnetic transition close to room temperature, thus enlarging the magnetic susceptibility of the compounds. The solid solutions at the morphotropic phase boundary exhibit a nearly twofold increase in piezoelectric response, whereas the magnetoelectric coupling shows five times enhancement in comparison with the parent bismuth ferrite. 相似文献
16.
The electronic structure and magnetic properties of the Ti2CoB Heusler compound with a high-ordered CuHg2Ti structure were investigated using the self-consistent full potential linearized augmented plane wave (FPLAPW) method within the density functional theory (DFT). Spin-polarized calculations show that the Ti2CoB compound is half-metallic ferromagnetic with a magnetic moment of 2 μB at the equilibrium lattice constant, a=5.74 Å. The Ti2CoB Heusler compound is ferromagnetic below the equilibrium lattice constant and ferrimagnetic above the equilibrium lattice constant. A large peak in majority-spin DOS and an energy gap in minority-spin DOS are observed at the Fermi level, yielding a spin polarization of 100%. A spin polarization higher than 90% is achieved for a wide range of lattice constants between 5.6 and 6.0 Å. 相似文献
17.
18.
S.K. Barik 《Solid State Communications》2011,151(24):1986-1989
We report the ac electrical response of La0.7Sr0.3Mn1−xFexO3(x=0.05) as a function of temperature, magnetic field (H) and frequency of radio frequency (rf) current (). The ac impedance (Z) was measured while rf current directly passes through the sample as well as in a coil surrounding the sample. It is found that with increasing frequency of the rf current, Z(T) shows an abrupt increase accompanied by a peak at the ferromagnetic Curie temperature. The peak decreases in magnitude and shifts down with increasing value of H. We find a magnetoimpedance of for at around room temperature when the rf current flows directly through the sample and when the rf current flows through a coil surrounding the sample. It is suggested that the magnetoimpedance observed is a consequence of suppression of transverse permeability which enhances skin depth for current flow. Our results indicate that the magnetic field control of high frequency impedance of manganites is more useful than direct current magnetoresistance for low-field applications. 相似文献
19.
Qiuhua Nie Tiefeng Xu Xiang Shen Xudong Zhang 《Journal of Physics and Chemistry of Solids》2007,68(4):477-481
A series of Er3+-doped Bi2O3-B2O3-SiO2-Na2O glasses with different hydroxyl groups were prepared and the interaction between the Er3+ ions and OH groups was investigated. Infrared spectra were measured in order to calculate the exact content of OH groups in samples. The observed increase of the fluorescence lifetime with the oxygen bubbling time has been related to the reduction in the OH content concentration evidenced by infrared (IR) absorption spectra, which confirmed that the OH groups were dominant quenching centers of excited Er3+ and a cause of concentration quenching of 1.5 μm band emission. Various nonradiative decay rates from 4I13/2 of Er3+ with the change of OH content were determined from the fluorescence lifetimes and radiative decay rates, which were calculated on the basis of Judd-Ofelt theory. 相似文献
20.
Brajendra Singh Ranjan K. Sahu S. Sundar Manoharan K. Drr K. -H. Müller 《Journal of magnetism and magnetic materials》2004,270(3):358-363
The substitutional effect of Ru on the magnetic and transport properties of double exchange ferromagnets, La0.7Sr0.3MnO3 and La0.5Sr0.5CoO3 has been investigated. It is found that substitution of 10% Ru at the Mn site of La0.7Sr0.3MnO3 decreases the Curie temperature by 20 K than that of the parent compound. However, a large decrease in the Curie temperature, ΔTc80 K and the system undergoes a transition from metallic state to insulating state is observed when 10% Ru is doped in La0.5Sr0.5CoO3. The marginal effect of Ru in the Mn–O–Mn sublattice in comparison to the Co–O–Co sublattice could be due to the magnetic exchange interaction between Mn and Ru by virtue of the fact that Ru exhibits variable valence states, Ru+4/Ru+5. The eg and t2g parentage of Ru+5 is similar to Mn+4 and therefore, Ru+5 ion appears to participate in the double exchange mediated ferromagnetic (FM) interaction. On the other hand, Ruthenium (IV) ion disrupts an intermediate spin state of cobalt (Co+3: t2g5eg1), forcing a double exchange FM state to anti-FM state. 相似文献