Perpendicular Exchange Coupling in TbFeCo/FePt Bilayer Films

We investigate the structure and exchange coupling in TbFeCo/FePt bilayer films. It is found that FePt has the L10 structure and the easy axis of the FePt film is perpendicular to the film plane. Results of the vibrating sample magnetometer and the magneto-optical Kerr effect measurements show a strong perpendicular exchange coupling between the ferrimagnetic TbFeCo layer and the hard ferromagnetic FePt layer. The magnetization direction of each layer and the process of magnetization reversal are discussed in detail. The switching field dependence on the exchange coupling has been modelled by micromagnetic simulation and the interlayer coupling constant is about -0.9 erg/cm^2 according to this simulation.     

Low-Temperature Magnetization Switching of Bilayer FeNi/FeMn Films

Journal of Experimental and Theoretical Physics - A change in the kinetics of magnetization reversal of a bilayer ferromagnet–antiferromagnet film during a decrease in the temperature is...     

Phase Diagram of Antiferromagnetically Exchange-Coupled Bilayer

Magnetic hysteresis properties of antiferromagnetically exchange-coupled bilayer structures, in which the two magnetic layers have different magnetic parameters and thicknesses, are studied within the framework of the Stoner-Wohlfarth model. Analytical expressions for the switching fields corresponding to the linear magnetic states are obtained. By adjusting the magnetic parameters or thicknesses of layers, nine different types of easy-axis hysteresis loops may exist. The phase diagram of easy-axis hysteresis loops is mapped in the k1 and k2 plane, where k1 and k2 are the ratios of magnetic anisotropy to the interlayer exchange coupling of the two magnetic layers, respectively.     

Micromagnetic Modeling of Spin-Wave Excitations in Corrugated YIG Films

Physics of the Solid State - In this paper, we study the features of the spin-wave excitation spectrum in a YIG film with a thickness of 0.4 μm and a magnetization of 1.1 kG corrugated due to...     

Magnetic Properties of Exchange-Coupled Dual-Layer SmTbCo Thin Films

Exchange-coupled SmTbCo dual-layer media are prepared by an r.f magnetron sputtering system and their magnetic properties are investigated. The prepared SmTbCo dual layer is composed of a 340 emu/cm^3 TM-rich readout layer and a 5.80 kOe RE-rich memory layer, meeting the requirements of high saturation magnetization and large coercivity for hybrid recording. Through exchange coupling, the coercivity of the high-saturation- magnetization SmTbCo layer is greatly enhanced from 1.85 to 5.96 kOe. The calculated interface wall energy for Sm6.65Tb12.35Co81 （20nm）/Sm1.22Tb42.16Co56.62 （20hm） is about 3.85erg/cm62. The reversal magnetization of the SmTbCo exchange-coupling dual-layer films is analysed based on a micro-magnetic model.     

Spin-Wave Resonance in Chemically Deposited Fe-Ni Films: Measuring the Spin-Wave Stiffness and Surface Anisotropy Constant

Single-layer Fe _x Ni_{1 - x} thin magnetic films have been investigated by the spin-wave resonance technique in the entire concentration range. The surface anisotropy and exchange stiffness constants for the films with a Ni content from 30 to 80 at % have been measured from the experimental standing spin wave spectra. The surface exchange spin wave penetration depth δ _C = 20–30 nm has been determined from the dependences of the surface anisotropy and exchange coupling constants on the Fe₂₀Ni₈₀ film thickness in the range of 250–400 nm.     

Interlayer interactions in FeNi/Bi/FeNi trilayers

Interlayer interactions in FeNi/Bi/FeNi films are studied experimentally. It is established by SQUID magnetometry and magnetic resonance investigations that the interlayer interaction in these films is determined by the bismuth spacer thickness and temperature. A giant magnetoresistance effect is observed in the investigated trilayers.     

Intrinsic Localized Spin-Wave Modes in an Anisotropic Ferromagnet with Dzyaloshinsky-Moriya Interaction

The existence and properties of intrinsic localized spin-wave modes in a ferromagnetic XXZ spin chain with Dzyaloshinsky-Moriya interaction are investigated analytically in the semiclassical limit. The model Hamiltonian is quantized by introducing the Dyson-Maleev transformation and the coherent state representation is chosen as the basic representation of the system. By making use of the method of multiple scales combined with a quasidiscreteness approximation, the equation of motion for the coherent-state amplitude is reduced to the nonlinear Schrödinger equation. It is shown that a bright intrinsic localized spin-wave mode whose eigenfrequency lies below the bottom of the magnon frequency band can exist in the ferromagnetic system. We also show that the system can produce a dark intrinsic localized spin-wave mode, i.e., nonpropagating kink, whose eigenfrequency is below the upper of the magnon frequency band. In addition, we find that the introduction of the Dzyaloshinsky-Moriya interaction changes wave numbers in the Brillouin-zone corresponding to the appearance of intrinsic localized spin-wave modes.     

Spin-Wave Resonance in Ge : Mn Thin Films with Percolation Magnetic Ordering

The mechanism of excitation and propagation of spin waves in Ge: Mn thin films with different nominal manganese concentrations (2, 4, and 8 at % Mn) with percolation magnetic ordering is explored. Concentration dependencies of Curie temperature T_C(n) and spin wave rigidity D(n) are determined, which enables to find the index of correlation distance. An exotic percolation magnetic state of samples of Ge: Mn thin films is confirmed by rectifying experimental dependences D(n) and D/T_C(n) in coordinates accepted in the percolation theory.     

Magnetic resonance studies of three-layer FeNi/Bi/FeNi films

The interlayer coupling in three-layer FeNi/Bi/FeNi films is studied by electron magnetic resonance. The magnetic anisotropy at the permalloy–bismuth interface is shown to play a significant role in the formation of the magnetic state of the film structure. The interlayer coupling oscillation period is found to be about 8 nm. The interlayer coupling and the interface anisotropy and their temperature dependences are determined.     

Nanoindentation Experimental Approach and Numerical Simulation of Al/Cr Bilayer Films

The Al/Cr double-layer film structure samples (thickness, 1200 nm) were prepared by the magnetron sputtering method. To investigate the mechanical properties, the samples were measured by using a nanoindentation instrument. The test results showed the nonlinearity and different modes of the main mechanical properties by comparing the macro-scale structure samples with other samples of similar materials. Based on the test, the elastic modulus and hardness of thin film structures can be calculated by considering different loads to conduct multi-point indentations. Meanwhile, the relationships between the mechanical parameters can be investigated based on these Al/Cr double-layer film structure samples. To validate the test, numerical analysis was developed using a finite element method to simulate the loading and unloading process of indentation. The simulation results were compared with the results of experiments to illustrate the validity of both the test and simulation to a certain extent. The investigation builds not only an experimental basis for practical applications for future study, but also supplies a complementary means of verification for theoretical analysis.     

Structural Phase Transformations in Al/Pt Bilayer Thin Films during the Solid-State Reaction

A sequence of phases forming during the solid-phase reaction in Al/Pt bilayer thin films has been investigated by in situ electron diffraction. It is shown that the amorphous PtAl₂ phase forms first during the solid-phase reaction initiated by heating. Upon further heating, PtAl₂, Pt₂Al₃, PtAl, and Pt₃Al crystalline phases sequentially form, which is qualitatively consistent with an effective formation heat model. The content of phases forming during the reaction has been quantitatively analyzed and the structural phase transformations have been examined.

     

Microstructure and magnetic properties of nanocomposite FePt/MgO and FePt/Ag films

An in-plane magnetic anisotropy of FePt film is obtained in the MgO 5 nm/FePt t nm/MgO 5 nm films (where t=5, 10 and 20 nm). Both the in-plane coercivity (H_c∥) and the perpendicular magnetic anisotropy of FePt films are increased when introducing an Ag-capped layer instead of MgO-capped layer. An in-plane coercivity is 3154 Oe for the MgO 5 nm/FePt 10 nm/MgO 5 nm film, and it can be increased to 4846 Oe as a 5 nm Ag-capped layer instead of MgO-capped layer. The transmission electron microscopy (TEM)-energy disperse spectrum (EDS) analysis shows that the Ag mainly distributed at the grain boundary of FePt, that leads the increase of the grain boundary energy, which will enhance coercivity and perpendicular magnetic anisotropy of FePt film.     

Magnetic domain wall pinning and coercivity in FePt/MgO and FePt/Pt thin films

FePt thin layers have been epitaxied either on Pt(0 0 1) or on MgO(0 0 1) substrates, and magnetically characterized using extraordinary Hall effect magnetometry and magnetic force microscopy. The coercivity originates in both cases from the pinning of domain walls on structural defects. Whereas the coercivity increases with the FePt layer thickness in FePt/Pt samples, it decreases in FePt/MgO samples. This discrepancy is explained on the basis of structural observations, and of atomistic simulations of magnetic domain wall pinning.     

Langmuir-Blodgett Films with Bilayer Alternation of Hemicyanine Dye and Cadmium Stearate

Multilayers consisting of bilayer alternation of hemicyanine dye and cadmium stearate have been prepared by the Langmuir-Blodgett technique. x-ray diffraction and optical absorption spectra are used to characterize their periodic structures and optical properties. The results show that a well ordered supperlattic is produced and the hemicyanine dye is in non-aggregated formation in the alternating multilayers.     

Subterahertz Longitudinal Phonon Modes Propagating in a Lipid Bilayer Immersed in an Aqueous Medium

The properties of subterahertz longitudinal acoustic phonon modes in the hydrophobic region of a lipid bilayer immersed in a compressible viscous aqueous medium are investigated theoretically. An approximate expression is obtained for the Mandelstam–Brillouin components of the dynamic structure factor of a bilayer. The analysis is based on a generalized hydrodynamic model of the “two-dimensional lipid bilayer + three-dimensional fluid medium” system, as well as on known sharp estimates for the frequencies and lifetimes of long-wavelength longitudinal acoustic phonons in a free hydrated lipid bilayer and in water, obtained from inelastic X-ray scattering experiments and molecular dynamics simulations. It is shown that, for characteristic values of the parameters of the membrane system, subterahertz longitudinal phonon-like excitations in the hydrophobic part of the bilayer are underdamped. In this case, the contribution of the viscous flow of the aqueous medium to the damping of a longitudinal membrane mode is small compared with the contribution of the lipid bilayer. Quantitative estimates of the damping ratio agree well with the experimental results for the vibration mode of the enzyme lysozyme in aqueous solution [1]. It is also shown that a coupling between longitudinal phonon modes of the bilayer and relaxation processes in its fluid environment gives rise to an additional peak in the scattering spectrum, which corresponds to a non-propagating mode.