Electronic structure and magnetic properties of metastable SmCo<Subscript>7</Subscript> compound

The electronic density of states, spin-splittings and atomic magnetic moments of SmCO₇-compound have been studied using spin-polarized MS-Xα method. The results show that a few of electrons are transferred to Sm(5d⁰) orbital because of orbital hybridization between Sm and Co atoms in the compound. The exchange interactions between 3d and 5d electrons lead to the magnetic coupling between Sm and Co, and therefore, result in the long-range ferromagnetic order inside the SmCo₇ compound. There are negative exchange couplings occurring at some levels, which weakens the strength of average coupling around Co lattice. So, the Curie temperature and Co-moment of SmCo₇-decrease distinctly compared with pure Co. Compared with SmCo₅ compound, the disordered substitution of Co-Co “dumbbell-atom” pairs for Sm changes the local environment of Co lattice, which makes the 2e site bear negative magnetic moment. The strength of hybridization near Fermi level weakens and the free energy of the compound increases obviously. Thus, SmCo₇ is a metastable compound at room temperature. Considering the localization of 4f electrons and a few of 5d electrons arising from the orbital hybridization, the magnetic moment of Sm atom will be 1.61μ_B in SmCo₇ compound, which is in agreement with the experimental values of Sm³⁺ ion-moment and Sm atom-moment in metals.     

Effect of conduction electrons on the law of approach to saturation of a metallic ferromagnet with surface pinning of the magnetic moment

The effect of conduction electrons on the magnetization curve of a metallic ferromagnet with surface pinning of the magnetic moment is investigated theoretically. The electronic contribution is due to the rearrangement of the discrete spectrum of charge carriers trapped by the nonuniform magnetic induction of such a ferromagnet, and it is a kind of diamagnetic effect that appreciably decreases the volume-averaged magnetization of the ferromagnet. A powerlaw dependence H ^−3/4 on the external magnetic field H is obtained according to the law of magnetization approach to saturation. This dependence is due to the contribution of the conduction electrons. Fiz. Tverd. Tela (St. Petersburg) 41, 647–653 (April 1999)     

Low-temperature structural anomalies in Pr<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript>

The magnetic and crystal structures of the Pr_0.5Sr_0.5CoO₃ metallic ferromagnet have been studied by the neutron diffraction technique. It is demonstrated that below 150 K, the compound is mesoscopically separated into two crystalline phases with different spatial symmetries and with different directions of the magnetic anisotropy. The phase separation exists down to 1.5 K, and at temperatures below 90 K, the low-symmetry phase occupies about 80% of the sample volume. The main structural difference between the phases is the configuration of oxygen atoms around praseodymium and, to a certain extent, around cobalt. The ferromagnetic structure with the magnetic moment lying in the basal plane of the structure (μ_Co ≈ 1.7 μ _B at 1.5 K) arises at 234 K, whereas the component directed along the long axis of the unit cell appears at 130 K. The formation of the new structural phase and change in the orientation of the magnetic moment give rise to the anomalies of the physical and magnetic characteristics of this compound observed earlier at temperatures about 120 K.     

Neutronenbeugungsuntersuchungen der magnetischen Struktur von TmCo3

The magnetic structure of the intermetallic TmCo₃ compound, determined by neutron diffraction measurements at 4.2 K on a powder sample, is colinear to the hexagonal c-axis, with the magnetic moments of Tm- and Co-ions being antiparallel coupled. The saturation moments have been found to beµ(Tm)=6.5µ _B andµ(Co)=0.8µ _B . The calculated magnetic moment of the Tm-ion by crystal field theory, based on a point charge model, is that of the free Tm³⁺ ion.     

Neutronenbeugungsuntersuchungen der magnetischen Struktur von TmCo3

The magnetic structure of the intermetallic TmCo₃ compound, determined by neutron diffraction measurements at 4.2 K on a powder sample, is colinear to the hexagonal c-axis, with the magnetic moments of Tm- and Co-ions being antiparallel coupled. The saturation moments have been found to beµ(Tm)=6.5µ _B andµ(Co)=0.8µ _B . The calculated magnetic moment of the Tm-ion by crystal field theory, based on a point charge model, is that of the free Tm³⁺ ion.     

Magnetic susceptibility and parameters of electronic structure of Al<Subscript>2</Subscript>REM (Gd,Dy, and Ho) intermetallic compounds at high temperatures

The magnetic susceptibility of Al₂REM (REM = Gd, Dy, and Ho) intermetallic compounds is experimentally investigated by the Faraday method in a wide temperature interval (290–2000 K) in different magnetic fields (0.3–1.3 T). In the crystalline state, the temperature dependences of the susceptibility follow the generalized Curie–Weiss law. In the liquid phase, the magnetic susceptibility of these intermetallic compounds above the melting point increases for all examined samples. The parameters of the electronic structure of the compounds are calculated based on the experimental data. It is established that the effective magnetic moment per rareearth metal atom is smaller than that characteristic of the free REM⁺ ion.     

Half-metallic properties of Ti2FeSi full-Heusler compound

In this study, the electronic structure and magnetic properties of novel half-metallic Ti₂FeSi full-Heusler compound with CuHg₂Ti-type structure were examined by density functional theory (DFT) calculations. The electronic band structures and density of states of the Ti₂FeSi compound show the spin-up electrons are metallic, but the spin-down bands are semiconductor with a gap of 0.45 eV, and the spin-flip gap is of 0.43 eV. Fe atom shows only a small magnetic moment and its magnetic moment is antiparallel to that of Ti atoms, which is indicative of ferrimagnetism in Ti₂FeSi compound. The Ti₂FeSi Heusler compound has a magnetic moment of 2 μ_B at the equilibrium lattice constant a=5.997 Å.     

First-principle study on electronic structure and magnetic properties of organic transition metal compound: Trans-tetrachloro-bis-(pyridine)-rhenium

The electronic structure and magnetic properties of the trans-tetrachloro-bis-(pyridine)-rhenium compound with the Re atom as the metallic magnetic center, were studied using the full potential linearized augmented plane wave method (FP-LAPW) within the density functional theory. The calculated total energies revealed that the compound has a stable antiferromagnetic (AFM) ground state, which is in agreement with the experiment. The band structure of the compound has a semiconductor character. The calculated magnetic moment per molecule is 3.00 μ_B, the magnetic moments are mainly from the Re atoms with a 5d³ electronic configuration. The AFM interaction between ferromagnetically coupled Re atom layers passes through the p orbitals of the Cl ligands near Re atoms.     

Interplay of structural, magnetic and transport properties in thelayered Co-based perovskite LnBaCo 2 O 5 (Ln = Tb, Dy, Ho)

The oxygen deficient cobaltites LnBaCo₂O₅ (Ln = Tb, Dy, Ho) exhibit two successive crystallographic transitions at T _N ∼340 K and at T _CO ∼210 K. Whereas the first transition (P4/mmm to Pmmm) is related to the long-range antiferromagnetic ordering of the Co ions (spin ordering), the second transition (Pmmm to Pmmb) corresponds to the long-range ordering of the Co²⁺ and Co³⁺ species (charge ordering) occurring in 1:1 ratio in the structure. The charge ordered (CO) state was directly evidenced by the observation of additional superstructure peaks using neutron and electron diffraction techniques. The CO state was also confirmed indirectly from refinement of high resolution neutron diffraction data as well as from resistivity and DSC measurements. From the refined saturated magnetic moment values only, ∼3.7 and ∼2.7 , the electronic configuration of the Co ions in LnBaCo₂O₅ remains conjectural. Two pictures, with Co³⁺ ions either in intermediate spin state ( t ⁵ _2g e ¹ _g ) or in high spin state ( t ⁴ _2g e ² _g ), describe equally well our experimental data. In both cases, the observed magnetic structure can be explained using the qualitative Goodenough-Kanamori rules for superexchange. Finally, in contrast to the parent Ln = Y compound [Vogt et al. , Phys. Rev. Lett. 84, 2969 (2000)], we do not report any spin transition in LnBaCo₂O₅ (Ln = Tb, Dy, Ho). Received 13 December 2000     

Magnetization and neutron scattering studies of the pressure effect on the magnetic transition in Er Y Co

Neutron powder diffraction was employed to study the pressure effect on the magnetic transition in the pseudobinary Laves-phase compound Er_0.57Y_0.43Co₂ and to determine the magnetic moments of the Er- and Co-subsystems. Our studies reveal that the onset of long-range magnetic order for both the localized 4 f (Er) and itinerant 3 d (Co) electron moments appears at about the same temperature at ambient pressure. The pressure effect on T_c is found to be negative and equal for both sublattices, namely T _c / p ∼ - 0.4 K/kbar. The values of the magnetic moments of the Er and the Co ions are found = 5.40±0.15μ _B /atom, = 0.50±0.07μ _B /atom and 5.35±0.15μ _B /atom, 0.37±0.09μ _B /atom, for p = 0 and 6 kbar, respectively. Our experimental results give evidence for short-range magnetic order formation at temperatures already above T_c and for a coexistence short- and long-range order below T_c down to 4 K. Received 20 December 2001 / Received in final form 12 June 2002 Published online 31 October 2002 RID="a" ID="a"e-mail: andrew.podlesnyak@psi.ch     

Hyperfine Field in Ferromagnetic CoPd Alloys

The magnetic hyperfine interaction of ⁶⁰Co in the completely miscible alloy Co _x Pd_1−x was investigated for different values of x by measuring the nuclear orientation of ⁶⁰Co as function of temperature and by nuclear magnetic resonance of the oriented ⁶⁰Co nuclei. A broad resonance signal of Gaussian shape could be observed down to x=60%. The dependence of the mean magnetic hyperfine field on the Co concentration was observed to be linear very similar to that of experimental values of the magnetic moment per atom in the literature. The magnetic hyperfine field and its broad distribution are discussed in a simple model with RKKY interaction. This revised version was published online in September 2006 with corrections to the Cover Date.     

Structural and magnetic properties and hyperfine interaction in La3.5Ru4O13 compound

Structural, magnetic and hyperfine interaction measurements have been carried out on the novel compound La_3.5Ru₄O₁₃ prepared under two different atmospheres (air and oxygen flow). This compound is formed in the orthorhombic structure (space group Pmmm, # 47). The coexistence of the triple-layered perovskite-type planes (quasi-2D structure) and the rutile-like slabs (1D structure) leads to interesting magnetic and electronic properties in this compound. The magnetic susceptibility of this system shows a peak at T~47 K associated with antiferromagnetic interactions. The Curie-Weiss behaviour of the susceptibility provides an effective magnetic moment consistent with Ru ions in low-spin state. Perturbed angular correlation measurements carried out with ¹¹¹Cd probe in the temperature range 10-60 K reveal only quadrupole interactions and indicate the occurrence of structural distortions for T<40 K.     

Probing the structural,bonding, electronic and magnetic properties of transition–metal borazine systems: Co m (borazine) n (m = 1, 2; n = 1–3)

ABSTRACT

The geometrical structures of neutral and anionic Co _m (borazine) _n (m?=?1, 2; n?=?1–3) complexes have been determined by using density functional theory. The results indicate that most of the ground state structures for the complexes are similar to those of Co _m (benzene) _n , which might because borazine is isoelectronic and isostructural to benzene. The frontier molecular orbitals (FMOs) analyses show that their FMOs mainly arise from the 3d/4s electrons of cobalt atoms and the weak π-cloud of borazine molecule. Furthermore, the magnetic moments of complexes were studied and the results revealed that the Co atoms carry most of the magnetic moments. Comparing with the magnetic moment of a free Co atom (3.0μ_B), the magnetic moments of Co atom in most of Co _m (borazine) _n ^0/- complexes are significantly reduced and even quenched except that the Co(borazine) remains unchanged. More importantly, there is a transition FM-to-AFM between neutral and anionic Co₂(borazine)₂. Finally, natural population analyses were performed to insightfully explore the reliable electronic structure properties.     

First-principles study on the electronic structure and the ferromagnetic properties of the cyano-bridged bimetallic compound Mn2(H2O)5Mo(CN)7·4H2O (α phase)

First-principles calculations have been performed to study the electronic structure and the ferromagnetic properties of the cyano-bridged bimetallic compound Mn₂(H₂O)₅Mo(CN)₇·4H₂O (α phase).The calculations were based on density-functional theory and the full potential linearized augmented plane wave method (FP-LAPW). The calculated total energies revealed that the compound has a stable ferromagnetic (FM) ground state, which is in agreement with the experiments. The electronic structure of the compound has a half-metallic behavior. The calculated magnetic moment per molecule is about 15.000 μ_B, the magnetic moment are mainly from Mo and Mn atoms with d electronic configuration. It is also found that there exists ferromagnetic interaction between low-spin Mo²⁺ and high-spin Mn³⁺ ions through the Mo-C-N-Mn linear linkages.     

Magnetic structure of Ce<Subscript>2</Subscript>Fe<Subscript>17 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> intermetallic compounds

The magnetic structure of intermetallic compounds Ce₂Fe_{17 − x} Mn _x (0 ≤ x ≤ 3) was studied using neutron diffraction. The neutron diffraction patterns measured at 4.2 K contain satellites indicating a modulated structure with the wave vector k = [0, 0, τ]. As the concentration x increases, the value of τ increases, while the average magnetic moment of Fe/Mn atoms decreases. A change in the magnitudes of the average magnetic moment and wave vector k is explained by competition between exchange interactions at distances of nearest neighbor transition element atoms.     

First-principles study of the ferromagnetic and half-metallic properties of the fumarate-bridged polymer

Density-functional theory (DFT) with generalized gradient approximation (GGA) is applied to study the electronic structure and the magnetic properties of ferromagnet [Cu( -C₄H₂O₄)(NH₃)₂] _n (H₂O) _m . The density of states, the electronic band structure and the spin magnetic moment are calculated. The calculations reveal that the compound has a stable half-metal-ferromagnetic ground state, and that there exists a dominant ferromagnetic interaction arising from the alkoxo-bridged dimeric part of the compound. The spin magnetic moment 1.0 per molecule mainly comes from the Cu ion with little contribution from O, N, C anion.Received: 5 October 2003, Published online: 12 July 2004PACS: 75.50.Xx Molecular magnetsK.L. Yao: wl-zl41@163.com     

Semiconductor-metal transition in FeSi in an ultrahigh magnetic field

We study the conductivity and magnetic susceptibility of single-crystal iron monosilicide in ultrahigh magnetic fields (up to 500 T) at low temperatures. The experimental methods used in measuring the conductivity and magnetic susceptibility are discussed. At 77K we detect a gradual increase in the conductivity of iron monosilicide by more than a factor of 100 as the magnetic field gets stronger. At 4.2K we detect a first-order phase transition in a field of 355 T accompanied by a sudden change in the value of the magnetic moment by 0.95 μ _B per iron atom and a transition to a phase with high conductivity. The results are discussed within the scope of the spin-fluctuation theory. Zh. éksp. Teor. Fiz. 116, 1770–1780 (November 1999)     

Magnetic properties of small amounts of iron dissolved in copper palladium alloys

The magnetic susceptibilities of copper-rich Cu_1−x Pd _x Fe _y alloys,x=0−0.40,y=30−300 ppm, have been measured in the temperature range 1.7 K–300 K. The results imply that an iron atom induces a magnetic moment of about 0.35μ _B on a nearest neighbour palladium atom. Conversely the effect of the nearest neighbour palladium atom on the iron atom itself leads to a stabilization of the iron moment indicated by a lowering of its Kondo temperature.     

Magnetic phases in quasi-binary (Fe1−x Cox)Ge2 intermetallic compounds

Magnetic neutron diffractometry revealed the existence in (Fe_1−x Co_x)Ge₂ solid solutions (x<0.5) with C16 structure of only two magnetic phases, namely, low-temperature (AFI) and high-temperature (AFII). A third magnetic phase, AFIII, suggested by earlier magnetic measurements, has not been found. The AFI and AFII phases have a commensurate and an incommensurate antiferromagnetic structure with the wave vectors k ₀=2π/a (1,0,0) and k=k ₀+δ k, respectively. The regions of their existence are shown in the magnetic phase diagram. Neutron diffraction measurements yielded the concentration dependence of the average magnetic moment per atom in the antiferromagnetic sublattice of a 3d metal, which, similarly to the dependence of the Néel point on x, was found to be nonlinear. An analysis of these dependences suggests that substitution of cobalt for iron is accompanied, on the one hand, by a decrease of the local spin density on the iron atoms in the nearest environment of a cobalt atom and, on the other hand, by an increase of the effective exchange integral between the nearest-neighbor iron atoms located along the tetragonal axis. Fiz. Tverd. Tela (St. Petersburg) 41, 283–289 (February 1999)     

NdNi2Ge2化合物的结构和电磁输运性质

利用非自耗真空电弧熔炼法制备了NdNi₂Ge₂化合物样品,采用X射线粉末衍射技术和Rietveld全谱拟合分析方法测定了其晶体结构. 结果显示该化合物的空间群为I4/mmm,点阵参数为:a=4.120(1),c=9.835(0),Z=2,Nd原子占据2a晶位,Ni原子占据4d晶位,Ge原子占据4e晶位. NdNi₂Ge₂化合物呈现顺磁性,应用居里-外斯定律拟合计算得到居里-外斯常数为25.8,居里-外斯温度为6.24 K. 有效势磁矩为3.69μ_B,这与理论计算Nd³⁺的磁矩相符,表明磁矩主要源于Nd³⁺. 电阻率变化范围为0.3 Ω ·μm^-1-1 Ω ·μm,电阻曲线拟合显示NdNi₂Ge₂呈半金属性. 关键词： 2Ge₂')" href="#">NdNi₂Ge₂ Rietveld结构精修 电磁输运