Low temperature properties of Ce(Pd1-xAgx)

Low temperature magnetic, transport and thermal measurements on the Ce(Pd_1-x Ag_x ) system, with x ranging from 0 to 0.17, are presented. The magnetic structure of the ordered phase transforms from ferromagnetic to antiferromagnetic with only 2at.% Pd substitution, whereas reentrance of ferromagnetism is observed at 15at.% Ag content. We propose the break in the periodicity of the Coulomb potential (Pd is a hole-like atom, whereas Ag is an electron-like one) as the dominant effect for such a change in the magnetic behavior of this system.     

The Electronic and Magnetic Properties of FCC Iron Clusters in FCC 4D Metals

The electronic and magnetic structures of small FCC iron clusters in FCC Rh, Pd and Ag were calculated using the discrete variational method as a function of cluster size and lattice relaxation. It was found that unrelaxed iron clusters, remain ferromagnetic as the cluster sizes increase, while for relaxed clusters antiferromagnetism develops as the size increases depending on the host metal. For iron in Rh the magnetic structure changes from ferromagnetic to antiferromagnetic for clusters as small as 13 Fe atoms, whereas for Fe in Ag antiferromagnetism is exhibited for clusters of 24 Fe atoms. On the hand, for Fe in Pd the transition from ferromagnetism to antiferromagnetism occurs for clusters as large as 42 Fe atoms. The difference in the magnetic trends of these Fe clusters is related to the electronic properties of the underlying metallic matrix. The local d densities of states, the magnetic moments and hyperfine parameters are calculated in the ferromagnetic and the antiferromagnetic regions. In addition, the average local moment in iron-palladium alloys is calculated and compared to experimental results.     

Ferromagnetism in fcc twinned 2.4 nm size Pd nanoparticles

The onset of ferromagnetism has been experimentally observed in small Pd particles of average diameter 2.4 nm. High-resolution studies reveal that a high percentage of the fcc particle exhibits single and multiple twinning boundaries. The spontaneous magnetization close to 0.02 emu/g seems to indicate that only a small fraction of atoms holds a permanent magnetic moment and contributes to ferromagnetism. The possible origin of ferromagnetism is briefly discussed according to different models recently reported.     

Features of magnetic resonance in nanoporous carbon with pores filled with transition-metal atoms

Properties of nanoporous carbon (NPC) free of metal atoms and NPC containing atoms of Ni, Co and Pd in their pores are studied by electron spin resonance (ESR). The asymmetrical ESR line with the so-called Dyson line shape points out that charge carriers are responsible for the resonance spectrum in metal-free NPC. Although the amount of Ni, Co, and Pd introduced into nanopores is small, the NPC properties change significantly. A bulk ferromagnetism is observed in the case of NPC with Co and Pd, but not in NPC:Ni. Co atoms in pores of NPC cause the formation of a new material, namely, a disordered ferromagnetic medium with some features in the Co atom distribution. Magnetic properties are strongly temperature-dependent. The temperature dependences of the conductivity and ESR integral intensity in NPC:Ni reveal an exponential growth with the same activation energy. The magnetic resonance spectrum of NPC:Pd consists of four signals for NPC which is produced from SiC. There are one ferromagnetic and three paramagnetic signals belonging to the carbon dangle sp³- and sp²-bonds kind and to the paramagnetic clusters of Pd atoms.     

Ferromagnetism of Pd(001) substrate induced by antiferromagnetic CoO

Our first-principles study has revealed unexpected spin polarization of the Pd(001) substrate in contact with antiferromagnetic CoO overlayers. We give an evidence that the ferromagnetism of Pd is caused by the zigzag positions of Co atoms with respect to the Pd interface, resulted from the lattice-mismatch driven structural relaxation. Because of the itinerant nature of its 4d electrons, we see that the ferromagnetic properties of Pd are highly sensitive to the local environment and can be enhanced further by increasing the thickness of CoO overlayer film or/and by applying an additional uniaxial pressure along c-axis exerted externally on the bottom layers of the Pd substrate. Our finding provides new functionality for the interfacial moments of the CoO/Pd system, which can be accessed experimentally, e.g., by the magneto-optical Kerr effect (MOKE) or/and by element-resolved X-ray magnetic circular dichroism (XMCD) measurement.     

Magnetic properties of charged spin-1 Bose gases with ferromagnetic coupling

The magnetic properties of a charged spin-1 Bose gas with ferromagnetic interactions are investigated within mean-field theory. It is shown that a competition between paramagnetism, diamagnetism and ferromagnetism exists in this system. It is shown that diamagnetism, being concerned with spontaneous magnetization, cannot exceed ferromagnetism in a very weak magnetic field. The critical value of reduced ferromagnetic coupling of the paramagnetic phase to ferromagnetic phase transition [Formula: see text] increases with increasing temperature. The Landé-factor g is introduced to describe the strength of the paramagnetic effect which comes from the spin degree of freedom. The magnetization density [Formula: see text] increases monotonically with g for fixed reduced ferromagnetic coupling [Formula: see text] as [Formula: see text]. In a weak magnetic field, ferromagnetism makes an immense contribution to the magnetization density. On the other hand, at a high magnetic field, the diamagnetism tends to saturate. Evidence for condensation can be seen in the magnetization density at a weak magnetic field.     

Size-induced ferromagnetism and metallicity in Nd0.5Sr0.5MnO3 nanoparticles: A neutron diffraction study

The phenomenon of destabilization of antiferromagnetic insulating state into a ferromagnetic metallic one in Nd_0.5Sr_0.5MnO₃ with the variation of particle/grain size is critically investigated. Based on our neutron diffraction study, magnetic and transport experiments, we observe ferromagnetism and metallic behavior in Nd_0.5Sr_0.5MnO₃ (∼40 nm grain size) as against A-type antiferromagnetic order in the sample with the largest grain size (∼800 nm). The latter shows a systematic change in the lattice parameters with temperature, and an antiferromagnetic ground state similar to that of a bulk system. Interestingly, the sample with the smallest grain sizes exhibits insignificant structural changes (compared to the largest grain size sample) but a complete change in the magnetic state (ferromagnetic behavior) as revealed from the neutron diffraction study. Magnetic measurements also confirm a ferromagnetic state in the small-grained sample. Electronic transport measurements exhibit a metal-insulator transition in this sample. The effects are primarily attributed to enhanced surface disorder.     

Structural,magnetic, and electrical properties of thin film Pd/Co layered structures

We report on properties of layered coherent structures of Pd and Co, prepared by RF sputtering. X-ray diffraction analysis characterizes these films as having a well-ordered periodic structure (periods λ in the range 10A < λ < 80A) of stacked (111) planes of fcc Co and Pd. Room temperature magnetic properties were measured with a vibrating sample magnetometer. All films are ferromagnetic, with a magnetic moment in excess of that attributable to Co. This excess, which increases as λ decreases, is interpreted as induced ferromagnetism in the Pd layers. The in-plane magnetization is harder for smaller values of λ and appears to depend mainly on the thickness of the Co layers. The in-plane electrical resistivity was measured in the range 2K–300K by a four-electrode method. Below 40K, the resistivity is dominated by residual resistivity; above this temperature, its rise is attributed mainly to the resistivities of bulk Pd and Co. The λ-dependence of the resistivity is described by a model of interfacial scattering of electrons. Evidence for the presence of coherency strains at small λ is present in the x-ray data, the magnetization behavior, as well as in the interfacial scattering mechanism deduced from the analysis of the resistivity.     

Ferromagnets based on diamond-like semiconductors GaSb,InSb, Ge,and Si supersaturated with manganese or iron impurities during laser-plasma deposition

Properties of thin (30–100 nm) layers of diluted magnetic semiconductors based on diamond-like compounds III–V (InSb and GaSb) and elemental semiconductors Ge and Si doped with 3d impurities of manganese and iron up to 15% were measured and discussed. The layers were grown by laser-plasma deposition onto heated single-crystal gallium arsenide or sapphire substrates. The ferromagnetism of layers with the Curie temperature up to 500 K appeared in observations of the ferromagnetic resonance, anomalous Hall effect, and magneto-optic Kerr effect. The carrier mobility of diluted magnetic semiconductors is a hundred times larger than that of the previously known highest temperature magnetic semiconductors, i.e., copper and chromium chalcogenides. The difference between changes in the magnetization with temperature in diluted semiconductors based on III–V, Ge, and Si was discussed. A complex structure of the ferromagnetic resonance spectrum in Si:Mn/GaAs was observed. The results of magnetic-force microscopy showed a weak correlation between the surface relief and magnetic inhomogeneity, which suggests that the ferromagnetism is caused by the 3d-impurity solid solution, rather than ferromagnetic phase inclusions.     

"Live" surface ferromagnetism in Fe nanodots/Cu multilayers on Cu(111)

We investigate the crossover behavior from two-dimensional (2D) to three-dimensional in multilayers of magnetic nanodots grown by stacking 2D Fe nanodot assemblies on Cu(111) single crystal substrate with a Cu spacing layer. Using an in situ magneto-optical Kerr effect, we have observed a striking ferromagnetic to spin-glass-like phase transition with an increasing number of Fe dot layers. The topmost layer of the Fe dots survives the phase transition and remains ferromagnetic. This unusual surface ferromagnetism is likely caused by a surface-state-mediated coupling which is stronger than the coupling in bulk layers. This is confirmed by the fact that the critical temperature of the surface ferromagnetism is considerably higher than that of the bulk spin-glass phase in the system.     

C、N、O掺杂CuBr和CuCl的电子结构和磁性的第一性原理研究

本文基于密度泛函理论(DFT)结合广义梯度近似(GGA),采用第一性原理的平面波赝势方法,探究非磁性sp元素(C、N和O)掺杂卤化物(Cu Cl和Cu Br)是否能诱导产生半金属铁磁性.通过计算体系总能量、能带、态密度和分态密度,分析了非磁性元素掺杂卤化物体系的电子结构和磁性;通过对材料加压,给出了体系铁磁性随压强变化的趋势并作了分析.最后计算显示,O和N掺杂能诱导Cu Cl产生稳定的半金属铁磁性,随着压强的增大Cu Cl0.75N0.25和Cu Cl0.75O0.25的铁磁性减弱最终发生磁相变由铁磁态(FM)转变为非铁磁态(NM).     

Spin-resolved inverse photoemission of ferromagnetic surfaces

Inverse photoemission (IPE) with spin-polarized electrons provides a way to measure separately the exchange-split majority and minority bands in ferromagnets above the Fermi level. Consequently spin-resolved IPE turns out to be an outstanding technique for obtaining information on surface magnetism: the magnetization of the topmost atomic layer may be investigated by measuring the exchange splitting of electronic states that are localized within the surface layer. Theoretical models of ferromagnetism may be tested by observing the temperature behavior of bands which contribute to the ferromagnetism of the material. The magnetic coupling of an adsorbate to the ferromagnetic substrate may be studied by probing adsorbate-induced bands. Results for the Ni(110) surface serve as an illustration to discuss the status of spin-resolved IPE and its application to the field of surface magnetism.     

Fe1-xPdx合金电子结构和磁性的理论研究

Fe1-xPdx合金的磁性强烈地依赖于其结构以及Pd的相对含量.从第一性原理出发，用线性缀加平面波(LAPW)方法，分别计算了x=000，025，050，075，100的情况下，面心立方(fcc)和体心立方(bcc)结构的Fe1-xPdx合金的电子结构和基态磁性.随x的增大，fcc结构的Fe1-xPdx合金的磁性从铁磁性或者反铁磁性变为亚铁磁性，再从亚铁磁性变为铁磁性和顺磁性；bcc结构的Fe1-xPdx合金从铁磁性减弱到顺磁性，预言了fcc结构的Fe1-xPdx合金可能存在亚铁磁相.并较好地解 关键词： 合金 电子结构 磁性     

Electron spin polarization esp at surfaces of ferromagnetic metals

Fundamental information on surface magnetic order (SMO) of ferromagnetic metals can be obtained from electron-capture, photoemission, fieldemission, spin-dependent tunneling and spin-polarized LEED experiments. The different techniques, new experimental advances and developments are discussed with particular emphasis given to electron-capture spectroscopy. This review will focus on new experimental and theoretical results (long-range and “local” SMO of ferro- and antiferromagnetic metals, surface states, SMO of thin films, new magnetic surface phases, magnetic surface reconstruction, chemisorption) obtained in the years past which have brought outstanding progress towards a deeper comprehension of the physics of ferromagnetism and towards the unravelling of the physical processes inherently involved in the various methods for spin spectroscopy. Recent data on the SMO received from experiments performed at surfaces of single crystals of 3d-TM and 4f-RE metals reveal new scientific insights and perspectives for the theoretical analysis of experimental results within the framework of the currently refined knowledge about ferromagnetism.     

Ferromagnetic resonance and magnetic force microscopy evidence for above room temperature ferromagnetism in Mn doped Si made by a solid state sintering process

Silicon doped with manganese made by a solid state sintering process starting with nanoparticles of Si and MnO is shown to be ferromagnetic above room temperature. The evidence for ferromagnetism is obtained from ferromagnetic resonance and magnetic force microscopy measurements. The magnetic force microscopy measurements show that the ferromagnetic resonance occurs in nanosized regions in the sample as has been suggested by Dietl. Raman and electric force microscopy measurements also suggest that then material is doped inhomogenously.     

Particle size dependence of the superconductivity and ferromagnetism in YBCO nanoparticles

Magnetic properties of superconducting yttrium barium copper oxide (YBa₂Cu₃O_7-δ) nanoparticles (31–43 nm) prepared by a chemical route have been studied. These nanoparticles have been found to clearly exhibit ferromagnetism at room temperature while superconducting transition is observed at lower temperatures. The low temperature hysteresis loops show evidence suggesting the presence of a large paramagnetic contribution in addition to the superconducting contributions from the particles. Bulk YBCO obtained by pelletizing and heating the same nanoparticles at a high temperature, displays the usual superconducting characteristics and gives no trace of ferromagnetism down to 10 K. The superconducting transition temperature of the nanoparticles is lower than for the bulk YBCO and there is a trend of decreasing T _c with smaller size of the particles. In contrast the ferromagnetic moment increases with decreasing particle size. The development of ferromagnetism is attributed to the presence of surface oxygen vacancies that lead to electron redistribution on the different ions at the surface. The simultaneous decrease of superconducting T _c and the increase of ferromagnetism with decreasing size considered as being reflective of the increased role of finite size and surface defects that weaken the superconductivity and enhance the ferromagnetism. Possible coexistence of surface ferromagnetism and bulk superconductivity at lower temperatures is discussed.     

Zn1-xMnxO纳米薄膜磁有序性的Monte Carlo模拟

基于Zn_1-xMn_xO纳米薄膜磁性研究的实验结果及相关理论,建立了一个包含多种交换作用的Ising多层膜模型,采用Monte Carlo模拟的Metropolis算法对于其铁磁序的成因进行了模拟研究.结果表明,Mn掺杂浓度(x)越低越有利于铁磁序的形成,但是x越低,系统的磁化强度越小,居里温度越低.载流子对铁磁序的形成所起的调节作用随着x的增大而增强,又随着磁各向异性常数(K)的增大而弱化.本 关键词： 稀磁半导体(DMS) 1-xMn_xO纳米薄膜')" href="#">Zn_1-xMn_xO纳米薄膜 Ising多层膜 Monte Carlo模拟     

First-Principles Study on Magnetic Properties of V-Doped ZnO Nanotubes

Electronic and magnetic properties of V-doped ZnO nanotubes in which one of Zn^2＋ ions is substituted by V^2＋ ions are studied by the first-principles calculations of plane wave ultra-soft pseudo-potential technology based on the spin-density function theory. The computational results reveal that spontaneous magnetization in Vdoped （9,0） ZnO nanotubes can be induced without p-type or n-type doping treatment, and the ferromagnetism is isotropic and independent of the chirality and diameter of the nanotubes. It is found that V-doped ZnO nanotubes have large magnetic moments and are ferromagnetic half-metal materials. Moreover, the ferromagnetic coupling among V atoms is generated by O 2p electron spins and V 3d electron spins localized at the exchanging interactions between magnetic transitional metal （TM） impurities. The appearance of ferromagnetism in V-doped ZnO nanotubes gives some reference to fabrication of a transparent ferromagnet which may have a great impact on industrial applications in magneto-optical devices.     

Room-temperature ferromagnetism in carbon-doped ZnO

We report ferromagnetism in carbon-doped ZnO. Our first-principles calculations based on density functional theory predicted a magnetic moment of 2.02 mu(B) per carbon when carbon substitutes oxygen in ZnO, and an ferromagnetic coupling among magnetic moments of the carbon dopants. The theoretical prediction was confirmed experimentally. C-doped ZnO films deposited by pulsed-laser deposition showed ferromagnetism with Curie temperatures higher than 400 K. The measured magnetic moment based on the content of carbide in the films [(1.5-3.0) mu(B) per carbon] was in agreement with the theoretical prediction. The magnetism is due to the Zn-C system in the ZnO environment.     

Ferromagnetism driven by intrinsic point defects in HfO(2)

In view of recent experimental reports of unexpected ferromagnetism in HfO(2) thin films, we carried out first-principles investigations looking for magnetic order possibly brought about by the presence of small concentrations of intrinsic point defects. Ab initio electronic structure calculations using density functional theory show that isolated cation vacancy sites in HfO(2) lead to the formation of high-spin defect states. Furthermore these appear to be ferromagnetically coupled with a rather short range magnetic interaction, resulting in a ferromagnetic ground state for the whole system. More interestingly, the occurrence of these high-spin states and ferromagnetism is in the low symmetry monoclinic phase of HfO(2). This is radically different from other systems previously known to exhibit point defect ferromagnetism, warranting a closer look at the phenomenon.