Structural and magnetic properties of transition metal oxide/metal bilayers prepared by in situ oxidation

Metal oxide/metal bilayers have been prepared by in situ oxidation. Ultrathin layers with antiferromagnetic properties are formed at room temperature by controlled in situ exposure of clean Fe, Co and Ni layers to pure oxygen gas. X-ray diffraction, Auger electron spectroscopy and transmisson electron microscopy have been applied to provide a detailed analysis of the layered structure. The magnetic properties of these antiferromagnetic/ferromagnetic bilayers are characterized by an interfacial coupling (exchange bias) which drastically varies with the type of antiferromagnetic material.     

Polarized neutron reflectometry of Fe/Cr/Gd superlattices

The magnetic structure of Fe/Cr/Gd superlattices is investigated using complementary methods of SQUID magnetometry and polarized neutron reflectometry. The complex magnetic behavior of the given system is caused by exchange interaction between the 3d (Fe) and 4f (Gd) layers of the ferromagnetic metals through the Cr antiferromagnetic spacer layer. It is found that a nonuniform profile of magnetization forms within the Gd layers under the influence of this interlayer interaction.     

Hydrogen-controlled interlayer exchange coupling in Fe/LaHx multilayers

Magneto-optic Kerr magnetometry and neutron reflectometry reveal that Fe layers exhibit magnetic exchange coupling through LaH_x spacer layers. Ferromagnetic and antiferromagnetic coupling is observed on multilayers of these materials depending on the thickness of the hydride layers, but without oscillatory behavior. Starting from metallic La dihydride spacer layers the effect of dissolving increasingly more hydrogen was examined. Sign and value of the coupling depend crucially on the hydrogen content x. The coupling can be inverted from antiferromagnetic to ferromagnetic and vice versa. These alterations are due to modifications of the electronic structure of the hydride. When the hydrogen absorption saturates the hydride layers become insulating and the exchange coupling is likely to disappear. In this final state the multilayers are always characterized by a very soft ferromagnetic rectangular hysteresis curve. Upon removal of the hydrogen to the initial concentration the original magnetic structure is restored.     

Magnetization reversal of elliptic Co/Si/Co nanodisks in the field of a magnetic-force microscope probe

The processes of local magnetization reversal of elliptic Co/Si/Co nanodisks under the action of a nonuniform magnetic field of a magnetic-force microscope (MFM) probe have been investigated. The specific features of the distribution of the phase MFM contrast from particles with ferromagnetic and antiferromagnetic configurations of the magnetic moments in neighboring Co layers have been discussed. It has been shown experimentally that, under the action of the probe field, there occur orientational transitions of two types: transitions from the ferromagnetic configuration to the antiferromagnetic configuration due to the reorientation of the magnetization of the upper layer and transitions in the antiferromagnetic configuration with a change in the orientation of the magnetic moment in both ferromagnetic layers. The presented results of micromagnetic simulation of the processes of transformation of the magnetization in such particles under the action of the MFM probe field explain the main regularities of the magnetization reversal processes.     

Predicted spin-orbit coupling effect on the magnetic ordering of crystalline uranium dioxide

The magnetic ordering of fluorite structure uranium dioxide has been investigated using fully-relativistic linear combinations of Gaussian type orbitals - fitting function (LCGTO-FF) calculations, within the generalized gradient approximation (GGA) to density functional theory. Three types of collinear spin-orderings were considered; ferromagnetic with spins aligned in the (001) direction and two antiferromagnetic (001) layer structures with spins aligned either perpendicular to each plane (001) or parallel to each plane (100). For each ordering, the total energy and spin-moment were calculated both with and without spin-orbit coupling. The ferromagnetic ordering is found to be energetically preferred to the antiferromagnetic orderings, contrary to experiment, whether or not spin-orbit coupling is included. Spin-orbit coupling is shown to have a significant quenching effect on the spin-moment and also introduces a strong magnetic anisotropy in the antiferromagnetic state that favors the (001) alignment over the (100) alignment.Received: 9 August 2003, Published online: 19 November 2003PACS: 71.15.Rf Relativistic effects - 75.25. + z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.) - 75.50.Ee Antiferromagnetics - 75.30.Gw Magnetic anisotropy - 64.30. + t Equations of state of specific substances     

Exchange bias in the IrMn/Co structures with alternative sequences of antiferromagnetic and ferromagnetic layers

The magnetic properties of Mo/IrMn/Co/Mo/SiO₂/Si structures with alternative sequences of the antiferromagnetic and ferromagnetic layers have been studied by measuring the angular dependence of the high-frequency radiation absorption in the ferromagnetic resonance region. The layers have been prepared by pulsed laser deposition in the absence of a magnetic field. It has been found that thermal annealing and cooling make it possible to create the exchange bias in the structure with the upper antiferromagnetic layer at a temperature much below the Néel temperature. At the same time, the identical heat treatment does not induce the exchange bias in the structure with the upper ferromagnetic layer. The possible mechanisms of the phenomena observed are discussed.     

Ultrathin multilayer of Fe and Ge: structure and magnetic properties

Metal-semiconductor multilayers are interesting, artificial structures as prospective candidates for spin injection devices. A Fe–Ge multilayer sample with very thin individual layers (few crystallographic planes) has been deposited by sputtering on Si[1 0 0] substrate. We have characterized the structure of this multilayer sample using X-ray diffraction, X-ray reflectometry and neutron reflectometry. The magnetic moment density in the ferromagnetic Fe layer has been obtained by polarized neutron reflectometry and the bulk magnetic behavior of the thin film by SQUID magnetometer measurements. We found that the film is a soft ferromagnet at room temperature with a substantially reduced magnetic moment of the Fe atoms.     

Antiferromagnetism of the FeNb and FeTa MU-phases

The magnetic structure of the antiferromagnetic FeNb and FeTa alloys has been investigated using a variety of techniques including susceptibility. Mössbauer and neutron diffraction measurements. Our results indicate a simple structure in which alternate Kagomé layers of Fe atoms have their moments oriented in opposite directions, approximately perpendicular to the plane of the layers. Positive Weiss temperatures confirm that the dominant nearest neighbour intra-layer interactions are ferromagnetic. Specific heat and low angle neutron scattering observations suggest extensive short-range order above T_N. The substantial non-magnetic contribution to the Mössbauer spectra is shown to result from ≈ 25% occupation of the high-coordination ‘A’ sites by Fe atoms with a similar proportion of the low-coordinationB2 Kagomé sites occupied by Nb. A structural neutron super lattice line too weak to have been observed in earlier work using X-rays suggests that the true μ-phase unit cell may be three times larger in dimensions than previously envisaged.     

Ordered magnetic frustration: IX. Magnetic structure of Ba2Ni3F10 at 2.5 K

The magnetic structure of Ba₂Ni₃F₁₀ at 2.5 K has been solved and refined from powder neutron diffraction data. Magnetic moments are oriented along [-1 0 1] perpendicularly to the rutile chains axis of the structure as in rutile NiF₂. Competition between strong antiferromagnetic and weak ferromagnetic interactions within even cycles of corner-sharing and edge-sharing octahedra leads to a frustrated antiferromagnetic coupling in bioctahedra units while non-frustrated rutile-like chains exhibit a normal ferromagnetic coupling.     

Modelling magnetic defects in antiferromagnetic alloys

A model for the distribution of magnetic moment in antiferromagnetic alloys is developed from a model for ferromagnetic alloys including a magnetic environment effect which has been successful for Ni alloys [5]. This model is compared with the Marshall model for neutron scattering from antiferromagnetic alloys, and the effect of atomic short range order on both models is discussed.     

Pressure-Induced Crossover From Two- to Three-Dimensional Magnetic Correlations in La 1.4 Sr 1.6 Mn 2 O 7 Manganite

Magnetic pressure-temperature phase diagram of La 1.4 Sr 1.6 Mn 2 O 7 layered manganese oxide has been studied by neutron diffraction. Three phases have been found in this compound at ambient pressure: high-temperature phase with quasi two-dimensional correlations of the magnetic moments on Mn sites and two low-temperature phases with long-range order - antiferromagnetic and ferromagnetic. Under hydrostatic pressure the antiferromagnetic phase is favoured with respect to the two-dimensional and long-range ferromagnetic phases. The magnetic phase with two-dimensional correlations is thus suppressed by the antiferromagnetic phase with long-range order. We discuss this result in terms of the pressure-induced electron transfer and compare our conclusions with predictions given by theoretical calculations.     

Magnetic phase transition in TbMn2Ge2

The crystal and magnetic stucture of TbMn₂Ge₂ are determined by neutron diffraction using a powder sample. The crystal structure of this compound is of the ThCr₂Si₂ type with small mixing of Mn and Ge atoms between 4(d) and 4(e) positions. At RT the antiferromagnetic collinear structure consist of a+?+? sequence of ferromagnetic layers of Mn atoms with the magnetic moment parallel to the c-axis. At 85 K, the ferromagnetic ordering within the Tb sublattice is observed. The magnetic moment (～7.7 μ_B) is parallel to the c-axis. At 4.2 K additional reflections are observed, which correspond to antiferromagnetic components in a monoclinic unit cell.     

Investigations of a quasi two-dimensional Heisenberg antiferromagnetic system. Nondeuterated and deuterated alkyl-ammonium-tetrachloromanganate

By neutron diffraction and susceptibility measurements the crystallographic and magnetic structures of (CH₃NH₃)₂MnCl₄ and (CD₃ND₃)₂MnCl₄ have been investigated. These compounds belong to a system of quasi two-dimensional Heisenberg antiferromagnets. At 96K a structural first order phase transition from the tetragonal high-temperature structure to an orthorhombic low-temperature structure was found. A magnetic phase transition from a two-dimensional antiferromagnetic preorder to a three-dimensional magnetic order occurs at 44.5K. The three-dimensional magnetic structure is characterized by antiferromagnetic (MnCl₄)^2- — layers perpendicular to the c-axis, with a ferromagnetic coupling between interacting next nearest (MnCl₄)^2- layers. The magnetic moments of the Mn-ions lie in the antiferromagnetic planes.     

Exchange couplings in magnetic films

Recent advances in the study of exchange couplings in magnetic films are introduced.To provide a comprehensive understanding of exchange coupling,we have designed different bilayers,trilayers and multilayers,such as anisotropic hard/soft-magnetic multilayer films,ferromagnetic/antiferromagnetic/ferromagnetic trilayers,[Pt/Co]/NiFe/NiO heterostructures,Co/NiO and Co/NiO/Fe trilayers on an anodic aluminum oxide(AAO) template.The exchange-coupling interaction between soft-and hard-magnetic phases,interlayer and interfacial exchange couplings and magnetic and magnetotransport properties in these magnetic films have been investigated in detail by adjusting the magnetic anisotropy of ferromagnetic layers and by changing the thickness of the spacer layer,ferromagnetic layer,and antiferromagnetic layer.Some particular physical phenomena have been observed and explained.     

Spin Wave Spectra in a Ferromagnetic/Non-magnetic Superlatt ice with Antiparallel Magnetization

The transfer-matrix method is employed to investigate the spin waves in a ferromagnetic/non-magnetic superlat tice with an antiferromagnetic coupling between interfacial ferromagnetic layers across a non-magnetic spacer layers and the an tiparaUel magnetizations between neighboring ferromagnetic films. The dispersion relation of the spin waves is obtained. The effects of the thickness of the magnetic layers, the antiferromagnetic coupling strength and concentration of magnetic atoms at the interface on the spin wave spectra are discussed in detail.     

Helicoidal magnetic structure of Ru2FeSi

Magnetic susceptibility, X-ray and neutron diffraction measurements have been performed on Ru₂FeSi intermetallic compound, which was found to be antiferromagnetic below 280 K. Neutron diffraction data obtained at 300 K indicate that Ru₂FeSi exhibits a chemically ordered structure with some admixture of L2₁ type of ordering. The magnetic ordering observed at 4.2 and 78 K consists of two components: - a collinear one formed by ferromagnetic (111) planes coupled antiferromagnetically, - an antiferromagnetic cone spiral with propagation vector k = 0.6a^*, parallel to the [001] direction. The total magnetic moment of 3.7μ_B at 4.2 K was found to be localized on iron ions only.     

Crystallographic and magnetic structures ofPr6Fe13Ge studied by powder neutron diffraction

Crystallographic and magnetic structures of Pr_6Fe_{13}Ge have been investigated by high-resolution powder neutron diffraction in the temperature range of 10－300 K. The magnetic structure consists of ferromagnetic Pr_6Fe_{13} slabs that alternate antiferromagnetically, along c, with the next Pr_6Fe_{13} slab separated by a non-magnetic Ge layer. The magnetic moments lie within the ab-planes. The propagation vector of this structure is k=(001) with respect to the conventional reciprocal lattice of the I-centred structure. However, the temperature-dependence of neutron-scattering intensity of the (110) Bragg peak, very similar to the temperature-dependent magnetization measured by SQUID magnetometer, indicates that a small c-axis ferromagnetic component should be added to the above antiferromagnetic model.     

Magnetization and magnetic susceptibility of the Ising ferromagnetic/antiferromagnetic superlattice

A linear cluster mean-field approximation is used to study the magnetic properties of the Ising ferromagnetic/antiferromagnetic superlattice, which is composed of a spin-1/2 ferromagnetic monolayer and a spin-1 antiferromagnetic monolayer with a single-ion anisotropy alternatively. By using the transfer matrix method, we calculate the magnetization and the initial magnetic susceptibility as functions of temperature for different interlayer coupling, single-ion anisotropy. We summarize the changing behaviors of the spin structure in ferromagnetic and antiferromagnetic layers and the characteristics of the corresponding magnetic susceptibilities, give the transition temperature as a function of the interlayer exchange coupling for different single-ion anisotropy, and analyze the features of the magnetization and the magnetic susceptibility.     

Nanoscale magnetic structure of ferromagnet/antiferromagnet manganite multilayers

We use polarized neutron reflectometry and dc magnetometry to obtain a comprehensive picture of the magnetic structure of a series of La(2/3)Sr(1/3)MnO3/Pr(2/3)Ca(1/3)MnO3 (LSMO/PCMO) superlattices, with varying thickness of the antiferromagnetic (AFM) PCMO layers (0相似文献   

Exchange bias in the IrMn/Co structures with alternative sequences of antiferromagnetic and ferromagnetic layers

JETP Letters - The magnetic properties of Mo/IrMn/Co/Mo/SiO2/Si structures with alternative sequences of the antiferromagnetic and ferromagnetic layers have been studied by measuring the angular...