Room Temperature Ferromagnetism of Mn Implanted AlInN

Ferromagnetic properties of Mn-implanted wurtzite AlxIn1-xN/GaN thin films grown by metal organic chemical vapor deposition (MOCVD) were observed using a quantum design superconducting quantum interference device (SQUID) magnetometer. Hysteresis behavior with a reasonably high saturation magnetic moment at room temperature for all the samples was noted, Two optical thresholds were observed at 1.58 and 2.64 eV, which are attributed to internal transition (E-5 -> T-5(2)) of Mn3+ (d(4)) and hole emission from the neutral Mn acceptor level to the valence band respectively. Bound magnetic polaron formation is considered to be the origin of ferromagnetism in our samples. (c) 2009 The Japan Society of Applied Physics

Possible origin of ferromagnetism in undoped anatase TiO2

Using first-principles electronic structure calculations we find that the titanium vacancy and divacancy may be responsible for the unexpected ferromagnetism in undoped anatase TiO2. An isolated titanium vacancy produces a magnetic moment of 3.5 mu(B), and an isolated titanium divacancy produces a magnetic moment of 2.0 mu(B). The origin of the collective magnetic moments is the holes introduced by the titanium vacancy or divacancy in the narrow nonbonding oxygen 2p(pi) band. At the center of the divacancy, an O-2 dimer forms during the relaxation, which lowers the total energy of the system and leads to the decrease in the total magnetic moment due to a hole compensation mechanism. For both the two native defects, the ferromagnetic state is more stable than the antiferromagnetic state.

Influence of Fe3+ on perovskite oxides: La2/3Ca1/3Mn1-xFexO3

The structure and magnetoresistance properties in sintered samples of La-2/3 Ca-1/3 Mn1-x FexO3 (0 less than or equal to x less than or equal to 0.84) are studied by using Mossbauer spectroscopy, XRD and magnetic measurement. There are antiferromagnetic interactions between Fe and its nearest neighbors (Fe, Mn) when 0 less than or equal to x less than or equal to 0.67, which are important factors influencing the double-exchange between Mn3+ and Mn4+, Curie temperature, magnetic moment and GMR. It is suggested that the Mn3+(Fe3+)/Mn4+ system also consists of magnetic clusters with different sizes.

Mossbauer spectroscopy study of Fe-57 in R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

Fe-57 Mossbauer spectra for the Fe atoms in the R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb, Dy; T=V, Cr) compounds were collected at 4.2 K. The analysis of Mossbauer spectra was based on the results of magnetization and neutron powder diffraction measurements. The average Fe magnetic moments at 4.2 K, deduced from our data, are in accord with magnetization measurements. The average hyperfine field of Tb3Fe29-xCrx (x=1.0, 1.5, 2.0, and 3.0) decreases with increasing Cr concentration, which is also in accordance with the variation of the average Fe magnetic moment in the Tb3Fe29-xCrx compounds.

High-field ferromagnetic resonance in fine particles

We investigate high-field ferromagnetic resonance of superparamagnetic particles with uniaxial anisotropy, In this case, since the field is large enough to saturate the magnetization, the thermal orientational fluctuations of the magnetic moment of the particle are negligible. Thus, we derive the dynamic susceptibility of the system on the basis of an independent particle model. High-field ferromagnetic resonance has been performed on fine cobalt particles, The analysis of the spectra obtained at different frequencies allows us to estimate the effective magnetic anisotropy, the gyromagnetic ratio, and the transverse relaxation time. (C) 1998 Elsevier Science B.V. All rights reserved.

Deviation from the stoichiometric composition of single-crystal 'Er2Co17'

The deviation from the stoichiometric composition of single-crystal 'Er2Co17' has been determined by theoretical analysis. It is found that the composition of this single-crystal 'Er2Co17' is rich in cobalt, and its real composition is suggested to be Er2-deltaCo17+2 delta (delta = 0.14) on the basis of a comparison of calculations based on the single-ion model with a series of experiments. The values of the Er-Co exchange field H-ex and the crystalline-electric-field (CEF) parameters A(n)(m) at the rare-earth (R) site in the 'Er2Co17' compound are also evaluated at the same time. The experiments provide the following data: the temperature dependence of the spontaneous magnetization of the compounds and the normalized magnetic moment of the Er ion, the magnetization curves dong the crystallographic axes at 4.2 K and 200 K, and the temperature dependence of the magnetization along the crystallographic axes in a field of 4 T.

Mossbauer spectroscopy study of Fe-57 in R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

Fe-57 Mossbauer spectra for the Fe atoms in the R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb, Dy; T=V, Cr) compounds were collected at 4.2 K. The analysis of Mossbauer spectra was based on the results of magnetization and neutron powder diffraction measurements. The average Fe magnetic moments at 4.2 K, deduced from our data, are in accord with magnetization measurements. The average hyperfine field of Tb3Fe29-xCrx (x=1.0, 1.5, 2.0, and 3.0) decreases with increasing Cr concentration, which is also in accordance with the variation of the average Fe magnetic moment in the Tb3Fe29-xCrx compounds.

High-field ferromagnetic resonance in fine particles

We investigate high-field ferromagnetic resonance of superparamagnetic particles with uniaxial anisotropy, In this case, since the field is large enough to saturate the magnetization, the thermal orientational fluctuations of the magnetic moment of the particle are negligible. Thus, we derive the dynamic susceptibility of the system on the basis of an independent particle model. High-field ferromagnetic resonance has been performed on fine cobalt particles, The analysis of the spectra obtained at different frequencies allows us to estimate the effective magnetic anisotropy, the gyromagnetic ratio, and the transverse relaxation time. (C) 1998 Elsevier Science B.V. All rights reserved.

Theoretical study of p-d hybridization in Co perovskite

The real-space recursion method and unrestricted Hartree-Fock approximation have been applied to calculate the density of states of various Co perovskite, CeCoO3, SrCoO3 and Sr1-xCexCoO3. We have studied the magnetically ordered states of these Co perovskites in an enlarged double cell, and find its various magnetic structures due to the occupancy of 3d band and its interaction with neighboring Co ions. In this study, we have studied the p-d hybridization of the three Co perovskites, we find t(2g) electrons are localized and the flat e(g) band is responsible for the itinerant behavior, and although the rare earth elements itself contribute little to the DOS at the Fermi energy, the DOS at Fermi energy and the magnetic moment changed consequently because of different valence of Co ions in these compounds and p-d hybridization effect is very important. (C) 2009 Elsevier B.V. All rights reserved.

Hyperfine quenching of the 3s3p P-3(0) level in Mg-like ions

Hyperfine quenching rates of the 3s3p P-3(0) level in Mg-like ions were calculated using the GRASP2K package based on the multi-configuration Dirac-Hartree-Fock method. Valence and core-valence correlation effects were accounted for in a systematic way. Breit interactions and QED effects were included in the subsequent relativistic CI calculations. Calculated rates were compared with other theoretical values and with experiment, and a good agreement with the latest experimental value for the Al-27(+) ion (Rosenband et al 2007 Phys. Rev. Lett. 98 220801) was found. Furthermore, we showed in detail the contributions from Breit interaction and QED effects to concerned physical properties. Finally, electronic data were presented in terms of a general scaling law in Z that, given isotopic nuclear spin and magnetic moment, allows hyperfine-induced decay rates to be estimated for any isotope along the isoelectronic sequence.

重子磁矩及粲重子谱研究

强子内部的有效自由度是强子物理研究的一个重要内容。本文利用含有五夸克成份的重子波函数计算了重子八重态的磁矩；利用含有偶夸克的弦模型研究单粲夸克重子谱。计算结果显示，在由轻夸克组成的重子八重态中，五夸克成分对粒子自旋磁矩有很大贡献；在含有重味夸克的重子中，将两个轻夸克近似看作偶夸克能得出合理的结果。磁矩和 衰变率的计算常常是检验重子模型是否合理的第一步。三夸克重子模型无法解释近些年来实验上发现的核子自旋丢失以及海夸克的非对称性等现象。三个价夸克与核子内的海夸克对可以形成瞬时稳定的五夸克态。邹冰松等在其模型中构造出这样一个态，它能同时给出奇异夸克对质子负的自旋贡献和正的磁矩贡献。而且该模型也能很好的解释夸克海中 被压低的实验结果。基于此模型，我们把奇异夸克的贡献推广到所有夸克贡献得出质子磁矩，然后由对称性构造其他八重态波函数并计算它们的磁矩。通过拟合实验，我们分析了重子内多夸克成分的几率，然后计算了 衰变系数以及轨道角动量对核子自旋的贡献等。含有重味夸克的重子是研究重子结构的一个非常理想的场所。近些年来，实验上发现了大量含粲夸克的重子，但是没有给出这些重子的宇称和角动量。通过分析单粲夸克重子谱，我们发现能级图中出现的劈裂可以分成宽度不同的两类。这可由引入两类偶夸克与粲夸克不同的的耦合给出解释。我们首先对含粲夸克重子按不同偶夸克进行了分类，进而给出部分粒子的宇称和角动量；然后利用A. Selem等推广的弦模型，计算了单粲夸克重子谱。 我们预测了实验上发现的一些高激发态的宇称和角动量同时给出了各种偶夸克的质量，并对其作了定性分析。我们还计算了含有粲夸克的五夸克态重子能谱。最后，对取得的结果作了讨论以及指出未来工作的方向

Near compensated half-metal in Sr2NiOsO6

The electronic and magnetic properties of tetragonal double perovskite Sr2NiOsO6 were studied by use of the density functional theory and including the spin-orbit coupling. Compensated half-metal is found if the spin-orbit coupling is not considered. Spin-orbit coupling induces orbital moments on both Ni and Os, making Sr2NiOsO6 a near compensated half-metal. Ferromagnetic phase is slightly favored over antiferromagnetic phase (by 4 meV). The small energy difference also suggests that both phases are competitive for the ground state. At ferromagnetic phase, the calculated net magnetic moment is 3.53 mu(B), in good agreement with experimental value of 3.44 mu(B). At antiferromagnetic phase, the net magnetic moment is 0.69 mu(B), in which the contribution from the net spin moment is 0.09 mu(B).

Half metallic properties of Sr2CuOsO6

The half metallic properties of the recent synthesized Sr2CuOsO6 were predicted by using the density functional theory. The effects of electron correlation and spin-orbit coupling (SOC) were studied. The calculations show that without considering SOC effect, Sr2CuOsO6 is half metallic and ferrimagnetic. By including both electron correlation and spin-orbit coupling, the total spin magnetic moment is 0.89 mu(B), total orbital moment 0.43 mu(B) in opposite direction, making the net magnetic moment 0.46 mu(B). SOC ruins the half metallic character. Crown Copyright (C) 2009 Published by Elsevier B. V. All rights reserved.

Structure and properties of the ordered double perovskites Sr2MWO6 (M = Co, Ni) by sol-gel route

The single-phase double perovskites Sr2MWO6 (M=Co, Ni) were prepared by sol-gel method. Crystal Structure, magnetic properties and the morphology of Sr2CoWO6 and Sr2NiWO6 were investigated. X-ray powder diffraction (XRD) analysis shows single phase structure for Sr2MWO6 (M=Co, Ni) without any traces of impurities and the crystal structure of all the samples belongs to the tetragonal I4/m space group. SEM image for Sr2MWO6 (M=Co, Ni) indicate that the grains are homogeneous and connect each other very well. The Neel temperature for Sr2CoWO6 and Sr2NiWO6 are 23 K and 59 K, respectively. Magnetic measurements showed that the magnetic moment in these double perovskites originates mainly from the interactions between Ni ions and Co ions.

Competition between band filling and steric effect in ordered double perovskites Sr2-xLaxMnMoO6

The ordered double perovskites, Sr2-xLaxMnMoO6, were prepared by sol-gel reaction. Structural, magnetic, and electrical properties were investigated for a series of ordered double perovskites Sr2-xLaxMnMoO6(0 <= x <= 1). The compounds have a monoclinic structure (space group P2(1)/n) and the cell volume expands monotonically with La doping. The T-C and the magnetic moment rise and the cusp-like transition temperature below which the magnetic frustration occurs shifts to high temperature as x increases. With La doping, electrical resistivity of Sr2-xLaxMnMoO6 decreases only at low doping levels (x <= 0.2); while at high doping levels (0.8 <= x <= 1), electrical resistivity tends to increase greatly. The results suggest that the competition between band filling effect and steric effect coexists in the whole doping range, and the formation of ferrimagnetic interactions is not simply at the expense of antiferromagnetic interactions.