Ferromagnetic Monolayer Research Articles

Thickness Dependence of Magnetic Properties of Co90Fe10 Nanoscale Thin Films

Ferromagnetic monolayers Co90Fe10 thin films with individual layer thicknesses 2, 6, and 8 nm were grown on thermally oxidized Si substrate and magnetic properties of these were investigated with Ferromagnetic resonance (FMR) technique at room temperature. The magnetoresistance (MR) of the samples were measured as a function of applied DC magnetic field and the thickness dependence of the MR was plotted. The FMR spectra were recorded for both parallel and perpendicular geometry. The X-band (9.5 GHz) FMR spectra and resonance field of samples were analyzed and fitted theoretically by using the Landau-Lifshits dynamic equation of motion for magnetization with the Bloch-Bloembergen type damping term. The computer programs have been written to extract the effective magnetization (M), g-values and spin-spin relaxation time (T2) fitting parameters. The thickness dependence of magnetic parameters has been obtained from experimental data by mean of a theoretical model.

Cantilever Stress Measurements of Ferromagnetic Monolayers

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Cantilever stress measurements of ferromagnetic monolayers

This overview summarizes important aspects of the cantilever stress measurement technique and its application to measurements of adsorbate-induced surface stress changes and magnetization-induced magnetoelastic stress (also called magnetostrictive stress) of ferromagnetic monolayers. The application of the cantilever technique as a torque magnetometer with monolayer sensitivity is demonstrated. The stress measurements indicate a correlation between surface stress changes and surface reconstruction, and they also identify the often decisive role of the magnetoelastic anisotropy for the non-bulklike magnetic anisotropy of ferromagnetic monolayers.

Ferromagnetic ordering and magnetic anisotropy of a Mn monolayer on Nb(001)

Through density functional full-potential linearized augmented-plane-wave calculations, we found that it is possible to materialize a ferromagnetic Mn monolayer on nonmagnetic Nb(001). It was obtained that the surface Nb atom has a large induced magnetic moment of $\ensuremath{-}0.56{\ensuremath{\mu}}_{B}$ and the Nb has an antiferromagnetic exchange interaction with the Mn adlayer. We attribute this antiferromagnetic exchange interaction between Mn and Nb atoms to the realization of a ferromagnetic ground state in a Mn monolayer on the Nb(001) surface. We also present the calculated results of x-ray magnetic circular dichroism and magnetic anisotropy. It was observed that $\mathrm{Mn}∕\mathrm{Nb}(001)$ has weak perpendicular magnetocrystalline anisotropy, but the easy axis is in plane due to the shape anisotropy.

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.

Anisotropy effects on the magnetic excitations of a ferromagnetic monolayer below and above the Curie temperature

The field-driven reorientation transition of an anisotropic ferromagnetic monolayer is studied within the context of a finite-temperature Green's function theory. The equilibrium state and the field dependence of the magnon energy gap $E_0$ are calculated for static magnetic field $H$ applied in plane along an easy or a hard axis. In the latter case, the in-plane reorientation of the magnetization is shown to be continuous at T=0, in agreement with free spin wave theory, and discontinuous at finite temperature $T>0$, in contrast with the prediction of mean field theory. The discontinuity in the orientation angle creates a jump in the magnon energy gap, and it is the reason why, for $T>0$, the energy does not go to zero at the reorientation field. Above the Curie temperature $T_C$, the magnon energy gap $E_0(H)$ vanishes for H=0 both in the easy and in the hard case. As $H$ is increased, the gap is found to increase almost linearly with $H$, but with different slopes depending on the field orientation. In particular, the slope is smaller when $H$ is along the hard axis. Such a magnetic anisotropy of the spin-wave energies is shown to persist well above $T_C$ ($T \approx 1.2 T_C$).

Theory of field-induced spin reorientation transition in thin Heisenberg films

We consider the spin reorientation transition in a ferromagnetic Heisenberg monolayer with a second order single ion anisotropy as a function of temperature and external field. Up to now analytical methods give satisfying results only for the special case that the external field is aligned parallel to the easy axis of the crystal. We propose a theory based on a generalization of the Callen decoupling, which can be used for arbritrary direction of the external field. Excellent agreement between our results and Quantum Monte Carlo data is found for the field induced reorientation at finite temperatures. Additionally, we discuss the temperature dependence of the transition in detail.

Reorientation Phase and Striped Domain Patterns of Thin Films

A ferromagnetic monolayer with competing long-range dipolar interaction, short-range interaction and magnetic uniaxial anisotropy is studied using Monte Carlo simulation. Striped domain patterns are found and reveal the microstructure of the magnetization transition at the ground state via the competing between dipolar interaction and uniaxial anisotropy. We present the finite temperature phase diagram and find a temperature-induced magnetization reorientation from out-of-plane to in-plane phase. The influence of the various interactions on the structure of the striped phase and reorientation behavior has been discussed.

Magnetic properties in the Ising-mixed spin- [formula omitted]-spin-1 superlattice

An expanded Bethe–Peierls approximation is used to study the magnetic properties of the magnetic superlattice, which consists of a mixed spin- 1 2 and spin-1 (with a single-ion anisotropy D) alternate ferromagnetic monolayers with antiferromagntic coupling at the interlayers. By using the transfer matrix method, we calculate the magnetization and the initial susceptibility as functions of temperature for different interlayer coupling, single-ion anisotropy and the relative intralayer interaction. We summarize the behaviors of the temperature dependence of the layered magnetizations, total magnetization and the initial susceptibility, and explain the reason that two peaks appears in the initial susceptibility curve in some parameter range.

Surface magnetic canting in a nonuniform film*1

The zero temperature equilibrium configuration of a nonuniform system made of a ferromagnetic (FM) monolayer on top of a semi-infinite FM film is calculated using a nonlinear mapping formulation of mean-field theory, where the surface is taken into account via an appropriate boundary condition. The analytical criterion for the existence of surface magnetic canting, previously obtained by Popov and Pappas, is also recovered.

Spin wave modes localised on a nano stripe with two dipole coupled layers

The peculiarities of magnetostatic resonances on a tri-layered (ferromagnetic/non-magnetic spacer/ferromagnetic) stripe have been studied. It has been shown that the role of dynamic demagnetising effects at the edges of the stripe depends on the symmetry of the mode: while in anti-symmetric “optical” modes the magnetisation practically vanishes at the edges, it remains definitely non-zero in the case of symmetric “acoustical” modes. In a tri-layer with non-identical ferromagnetic mono-layers, the structure of an individual mode can become extremely complex and asymmetric. Typically, it contains two spatial harmonics, which means that every single mode will produce two optical responses in a Brillouin spectrometer, and the distribution of the dynamic magnetisation in layers differs significantly. To quantify the investigated effects the analytical technique, developed earlier for mono-layered stripes, has been extended to the multilayer case.

Surface magnetic canting in a nonuniform film

Abstract The zero temperature equilibrium configuration of a nonuniform system made of a ferromagnetic (FM) monolayer on top of a semi-infinite FM film is calculated using a nonlinear mapping formulation of mean-field theory, where the surface is taken into account via an appropriate boundary condition. The analytical criterion for the existence of surface magnetic canting, previously obtained by Popov and Pappas, is also recovered.

Ferromagnetic Monolayers. A Fresh Look at Fundamentals

AbstractFor Abstract see ChemInform Abstract in Full Text.

Spectral theorem of many-body Green’s function theory when there are zero eigenvalues of the matrix governing the equations of motion

In using the spectral theorem of many-body Green's function theory in order to relate correlations to commutator Green's functions, it is necessary in the standard procedure to consider the anti-commutator Green's functions as well whenever the matrix governing the equations of motion for the commutator Green's functions has zero eigenvalues. We show that a singular-value decomposition of this matrix allows one to reformulate the problem in terms of a smaller set of Green's functions with an associated matrix having no zero eigenvalues, thus eliminating the need for the anti-commutator functions. The procedure is quite general and easy to apply. It is illustrated for the field-induced reorientation of the magnetization of a ferromagnetic Heisenberg monolayer and it is expected to work for more complicated cases as well.

Ferromagnetic monolayers: a fresh look at fundamentals

AbstractThe preparation of single ferromagnetic layers in ultrahigh vacuum provides interesting new phenomena in magnetism. Three examples will be given: (i) Pseudomorphic growth of Ni, Co, Fe on fcc‐Cu single crystals produces ferromagnets with tetragonal and trigonal symmetry. This enlarges the magnetic anisotropy energy (hard magnets) by several orders of magnitude. (ii) In two‐dimensional ferromagnetic films the spin‐fluctuations are much more dominant than in bulk ferromagnets. As a result the magnetic ordering temperature of coupled ferromagnets can be shifted by 50–100 K. (iii) By varying the film thickness the Curie‐temperature can be shifted to any convenient value. This allows to study in a detailed manner critical phenomena, e.g. the critical exponent γ for Fe/V‐multilayers.

First-principles study on the electronic structures of iron phthalocyanine monolayer

The electronic band structure and magnetic properties of iron phthalocyanine (FePc) monolayer were investigated by using the first-principles all-electron full-potential linearized augmented plane wave energy band method. It is found that the ferromagnetic FePc monolayer is energetically more stable than the paramagnetic one. The exchange interaction, which splits the majority and minority bands, influences strongly on the electronic structure near the Fermi level ( E F). Magnetic moment of the central Fe atom is calculated to 1.95 μ B. The range of the positive polarization of Fe site is larger in the out-of-plane than in the in-plane direction. The FePc ligand remains paramagnetic. The presence of states at E F indicates the metallic character of FePc monolayer both for the paramagnetic and ferromagnetic states. However, the large density of states at E F of the majority spins in the ferromagnetic state is expected to cause a phase transition to insulating antiferromagnetic state from the metallic ferromagnetic one.

In-plane dipole coupling anisotropy of a square ferromagnetic Heisenberg monolayer

In this study we calculate the dipole-coupling-induced quartic in-plane anisotropy of a square ferromagnetic Heisenberg monolayer. This anisotropy increases with an increasing temperature, reaching its maximum value close to the Curie temperature of the system. At $T=0$ the system is isotropic, besides a small remaining anisotropy due to the zero-point motion of quantum mechanical spins. The reason for the dipole-coupling-induced anisotropy is the disturbance of the square spin lattice due to thermal fluctuations (``order-by-disorder'' effect). For usual ferromagnets its strength is small as compared to other anisotropic contributions, and decreases by application of an external magnetic field. The results are obtained from a Heisenberg Hamiltonian by application of a mean field approach for a spin cluster, as well as from a many-body Green's function theory within the Tyablikov decoupling (the random phase approximation).

Embedded Green-function approach to the ballistic electron transport through an interface

We present an efficient method for calculating the conductance of ballistic electrons through an interface from first principles using the embedding approach of Inglesfield. In our method the Landauer-B\uttiker formula for ballistic transport is expressed in terms of two quantities that are available in the embedded Green-function formalism without additional calculations. One is the embedding potential of bulk crystals on both sides of the interface and the other is the Green function in the interface region. As a proof of principle we calculate on the basis of the density-functional theory the spin-resolved electron transmission through a model system of ferromagnetic Co monolayers sandwiched between bulk Cu crystals. The relationship between our formulation and the Green-function formulation of Baranger and Stone is discussed.

The Spin-Wave Contribution to the Heat Capacity of Ferromagnetic Thin Films

A Heisenberg model is solved within the spin-wave theory for thin films in which ferromagnetic monolayers are separated by nonmagnetic spacer layers. The interface interaction is assumed to be ferromagnetic. We have included also a magnetic anisotropy in each monolayer. The temperature dependence of the spin-wave contribution to the heat capacity C m in such composite systems is derived for several sets of material parameters and for different film thicknesses.

The spin-wave contribution to the heat capacity of ferromagnetic thin films with variable interlayer couplings

A Heisenberg model is solved within the spin-wave theory for thin films in which ferromagnetic monolayers are separated by nonmagnetic spacer layers. The interface interaction is assumed to be ferromagnetic. We have included also a magnetic anisotropy in each manolayer. The temperature dependence of the spin-wave contribution to the heat capacity C m in such composite systems is derived for different interlayer couplings and for different film thickness.