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1.
The electronic structures of CaCu3Mn4O12 and CaCu3Ti4O12 are investigated from HF SCF LCAO calculation. In CaCu3Mn4O12, the band and the density of states show a spin asymmetric ferrimagnetic character with a small energy gap. The Mn spin is anti-aligned with the Cu spin, and the total spin moment is 9 μB. Our calculation correctly reproduces the observed antiferromagnetic insulating character of CaCu3Ti4O12. The gap in the band structure, which is 2.15 eV, reasonably agrees with the experimental value 1.5 eV. The electron density populations at different planes show clearly that the electron density has symmetric character. A tilted Mn(Ti) orbital implies a typical tilted three-dimensional network of MnO6 (TiO6) octahedra due to doping of the Jahn–Teller ion Cu. There is no covalency between Ca, Cu and Mn(Ti) atoms. In contrast, there are stronger bonds and somewhat likely covalency between Cu and O atoms, and also between Mn(Ti) and O atoms. 相似文献
2.
T. Jeong 《Solid State Communications》2006,138(5):261-264
The electronic structure of Y4Co3 has been studied based on the density functional theory within the local-density approximation. The calculation indicates that Y4Co3 is very close to ferromagnetic instability. The Fermi surfaces are composed mainly of 3d electrons of Co and 4d electrons of Y. 相似文献
3.
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
4.
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
5.
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
6.
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
7.
Epitaxial and c-axis oriented double perovskite Sr2CrWO6 thin films were prepared on SrTiO3 (100) and LaAlO3 (100) substrates by pulsed-laser deposition. Structural, magnetic and transport properties were found to be sensitive to the gas conditions employed during the deposition. A small amount of oxygen along with Ar during the deposition was found to be essential for B-site ordering; such films displayed lattice parameters close to the bulk value and display ferromagnetic metallic behavior. The Curie temperature observed above 500 K in these films is higher than bulk Sr2CrWO6 samples. Films grown without oxygen were observed to have long c-parameter and no B-site ordering; they were non-magnetic and semiconducting. 相似文献
8.
K. Miyamoto K. IoriA. Kimura T. XieM. Taniguchi S. QiaoK. Tsuchiya 《Solid State Communications》2003,128(5):163-166
Co and Mn 2p core absorption (XAS) and X-ray magnetic circular dichroism (XMCD) spectra have been measured for the ferromagnetic ternary alloy Co2MnGe. The observed Co 2p XAS spectrum can be understood on the basis of the unoccupied Co 3d partial density of states, whereas the overall features of the Mn 2p XAS and XMCD spectra have been partly reproduced by the Mn 2p53d6 final state multiplets. We have found that the orbital polarization of the Co 3d and even the Mn 3d states are recognizable, which suggests that a spin-orbit coupling should be taken into account in the energy band structure in order to reproduce the half metallic nature of this alloy. 相似文献
9.
Neutron powder diffraction experiments performed on two selected compositions of the yttrium-based solid solution YNixMn1−xO3 clearly reveal a nuclear order between the Ni2+ and Mn4+ ions in the half-substituted compound YNi0.50Mn0.50O3, so that the crystal structure is no longer described in the conventional orthorhombic Pbnm space group, but in the monoclinic P21/n, all over the investigated temperature range (1.5-300 K). However, both X-rays diagrams and neutron patterns of the YNi0.25Mn0.75O3 phase are indexed in the Pbnm orthorhombic-like symmetry, indicating that the Mn and Ni ions are randomly distributed on the octahedral sites.In addition, neutron diffraction points out that the nature of the magnetic ordering is strongly connected to the structural properties. Whereas no long-range 3D-magnetic ordering was detected for the Pbnm YNi0.25Mn0.75O3 phase, the YNi0.50Mn0.50O3 compound exhibits a magnetic transition at The magnetic structure consists of two collinear Mn4+ and Ni2+ ferromagnetic layers (Fx0Fz magnetic configurations) with saturated magnetic moment values of 2.25(2) and 1.57(2) μB for Mn4+ and Ni2+, respectively, at 1.5 K. 相似文献
10.
11.
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
12.
13.
The η-Mo4O11 compound is a layered two-dimensional (2D) metallic system whose reduced dimensionality originates non-linear properties as charge density wave (CDW) instabilities. We report on synchrotron radiation angle resolved photoemission spectroscopy (ARPES) measurements in order to obtain a detailed picture of the electronic structure of this material. The symmetry of the states near the Fermi level (EF) has been discussed in relation to the photoemission symmetry selections rules. Our results are in excellent agreement with previous tight-binding calculations and support the hidden nesting concept proposed to explain the CDW instabilities exhibited by this family of compounds. In addition, a very peculiar photoemission line-shape has been found with the presence of localized non-dispersive states. Some possible explanations are discussed. 相似文献
14.
Rare-earth-based manganites ABO3 may present interesting properties when the lanthanide (A-site) and/or the manganese (B-site) are partially substituted by divalent elements. Heavy lanthanides are particularly appealing because of the expected interplay between the intrinsic magnetic properties of the rare-earth element (Ln) and those of the ferromagnetic manganese sublattice. As such, a spin reorientation has been observed during magnetization-versus-temperature cycles due to a negative exchange interaction between Mn and Ln. We present herein high-quality epitaxial thin films (∼200 nm thick) of Gd0.67Ca0.33MnO3 deposited onto (1 0 0) SrTiO3 substrates by pulsed-laser deposition. Enhanced properties were observed in comparison with bulk samples. The magnetic transition temperature Tc of the as-grown films is much higher than the corresponding bulk values. Most interesting, magnetization measurements performed under small applied fields, exhibit magnetization reversals below Tc, no matter whether the film is field-cooled (FC) or zero-field-cooled (ZFC). The reversal mechanism is discussed in terms of a negative exchange f-d interaction and magnetic anisotropy, this latter enhanced by strain effects induced by the lattice mismatch between the film and the substrate. 相似文献
15.
D. Baldomir V. Pardo S. Blanco-Canosa D.I. Khomskii A. Piñeiro J.E. Arias 《Journal of magnetism and magnetic materials》2009,321(7):679-681
Electronic structure calculations were performed for ZnV2O4, a material close to a metal-insulator transition. Structural optimization leads to the formation of V-V dimers along the off-plane chains. A strong spin-lattice coupling is expected close to the transition to itinerancy. No orbital ordering is observed in such a structure, and the experimentally found magnetic structure is naturally explained. 相似文献
16.
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
17.
N.N. Delyagin A.L. ErzinkyanV.P. Parfenova I.N. RozantsevG.K. Ryasny 《Journal of magnetism and magnetic materials》2008
The ferromagnetic-to-antiferromagnetic transition in the hexagonal (Hf1−xTix)Fe2 (0?x?1) intermetallic compounds has been investigated by 57Fe Mössbauer spectroscopy. At 10 K, the transition occurs within rather narrow concentration limits, around x=0.55–0.65. We found that the key factor governing the unexpected quick change of the magnetic structure is the magnetic frustration of the Fe(2a) sites. The magnetic frustration is caused by the noncollinearity of the Fe(6h) magnetic sublattice. The noncollinearity arises from the rotation of the magnetic moments due to the competition between the ferromagnetic exchange interactions and the antiferromagnetic Fe(6h)–Ti–Fe(6h) interaction. In the compounds with x=0.4–0.6, the temperature transitions to the antiferromagnetic state are observed. As an example, the Hf0.4Ti0.6Fe2 compound is completely antiferromagnetic above 200 K. 相似文献
18.
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
19.
A. Elmali 《Solid State Communications》2004,130(7):455-458
The structure and magnetic properties of La1−xTbxMn2Si2 (0≤x≤0.3) were studied by X-ray powder diffraction and DC magnetization measurements. All the compounds crystallize in ThCr2Si2-type structure. Substitution of Tb for La led to a linear decrease in the lattice constants and the unit-cell volume. A ferromagnetic phase for x≤0.15, and an antiferromagnetic phase for x=0.3 have been observed at about room temperature, whereas the compounds with x=0.2 and 0.25 exhibit a magnetic phase transition from ferromagnetism to antiferromagnetism. 相似文献
20.
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