Jinjin Yue

Texture induced magnetic anisotropy in Fe3O4 films

This letter reports a free energy density model for textured films in which the related physical concept and expression of magneto-texture anisotropy energy are presented. The structural characterization and out-of-plane angular dependence ferromagnetic resonance of strongly textured Fe3O4 films were systematically investigated. We found that the typical free energy density model for polycrystalline film cannot be applied to the textured films. With the introduction of magneto-texture anisotropy energy in the free energy density model for thin films, we simulated and quantitatively determined the competing anisotropies in (111)-textured Fe3O4 films.

Enhancing the Spin–Orbit Coupling in Fe3O4 Epitaxial Thin Films by Interface Engineering

By analyzing the in-plane angular dependence of ferromagnetic resonance linewidth, we show that the Gilbert damping constant in ultrathin Fe3O4 epitaxial films on GaAs substrate can be enhanced by thickness reduction and oxygen vacancies in the interface. At the same time, the uniaxial magnetic anisotropy due to the interface effect becomes significant. Using the element-specific technique of X-ray magnetic circular dichroism, we find that the orbital-to-spin moment ratio increases with decreasing film thickness, in full agreement with the increase in the Gilbert damping obtained for these ultrathin single-crystal films. Combined with the first-principle calculations, the results suggest that the bonding with Fe and Ga or As ions and the ionic distortion near the interface, as well as the FeO defects and oxygen vacancies, may increase the spin-orbit coupling in ultrathin Fe3O4 epitaxial films and in turn provide an enhanced damping.

One-dimensional zinc ferrite nano-chains synthesis by chemical self-assembly assistant by magnetic field

A series of zinc ferrite chains have been synthesized successfully by using the self-assembly method in different synthesizing magnetic fields. The particle chains are arranged in order on the Si substrate under the assistant magnetic field. The zinc ferrite chains show various length-to-radius aspect ratio, saturation magnetization Ms, remanent magnetization Mr, and coercivity Hc in the corresponding synthesizing magnetic fields. Using X-ray magnetic circular dichroism, the Zn substitution mechanism in the ferrite chains has been analyzed and discussed.

The investigation of ferromagnetic resonance linewidth in Ni80Fe20 films with submicron rectangular elements

Patterned magnetic films with nano-scaled dots exhibit some special magnetic properties. In this paper, we investigate the in-plane shape anisotropy and the magnetization dynamic damping in permalloy (Ni80Fe20) arrays of submicron rectangular elements using ferromagnetic resonance (FMR). The FMR linewidth exhibits a dependence on the element size, and mainly comes from the contribution of the intrinsic damping. Also the contribution of two-magnon scattering plays an important role and is reduced with increasing aspect ratio. The damping coefficient decreases from 0.0129 to 0.0118 with the element length increasing from 300 nm to 1200 nm, and the theoretical calculation suggests that the change of damping results from the longitudinal and transverse interlayer spin current due to the spatially inhomogeneous magnetization dynamics.

The influence of interface on spin pumping effect in Ni80Fe20 /Tb bilayer

Focusing on the interface effect of the Ni80Fe20 (Py)/terbium (Tb) bilayer, the influence of interface on the magnetization dynamic damping is investigated systematically. Two series of Py (12 nm)/Tb (d nm) films with and without copper (Cu) (1 nm) interlayer are deposited on silicon (Si) substrates by DC magnetronsputtering at room temperature. From vibrating sample magnetometer (VSM) measurements, the saturation magnetization (Ms) decreases with increasing Tb thickness in Py/Tb bilayer while the decrease of Ms is suppressed efficiently by inserting a Cu layer with even 1 nm of thickness. From the frequency dependence of ferromagnetic resonance (FMR) linewidth, we can obtain the Gilbert damping coefficient (α), α is found to exhibit an extreme enhancement in comparison to the single Py layer and shows an increasing trend with increasing Tb thickness. By inserting the Cu layer, α decreases significantly. From theoretical fitting, the spin diffusion length (λSD) and spin mixing conductance (g↑↓) are determined. It shows that the interface structure influences the spin mixing conductance but not the spin diffusion length.

Effect of spacer layer on the magnetization dynamics of permalloy/rare-earth/permalloy trilayers

The permalloy/rare-earth/permalloy trilayers with different types (Gd and Nd) and thicknesses of spacer layer are investigated using frequency dependence of ferromagnetic resonance (FMR) measurements at room temperature, which shows different behaviors with different rare earth spacer layers. By fitting the frequency dependence of the FMR resonance field and linewidth, we find that the in-plane uniaxial anisotropy retains its value for all samples, the perpendicular anisotropy remains almost unchanged for different thickness of Gd layer but the values are tailored by different thicknesses of Nd layer. The Gilbert damping is almost unchanged with different thicknesses of Gd; however, the Gilbert damping is significantly enhanced from 8.4×10−3 to 20.1×10−3 with 6 nm of Nd and then flatten out when the Nd thickness rises above 6 nm.

The magnetic properties of well-aligned nickel nanochains synthesized by magnetic field-induced assembly approach

Highly uniform one-dimensional Ni chains with controllable diameters and lengths have been synthesized at 70 °C by a hydrothermal process under a 0.35 T induced magnetic field. The diameter of the spheres in the magnetic Ni chains is adjusted from 80 nm to 1000 nm with the chain length changed from 1.2 μm to 50 μm by varying the concentration of ethylene glycol and potassium hydroxide in the solution. The Ni chains with different length-to-diameter aspect ratio show the different particle shape and interparticle spacing. Magnetic hysteresis loop measurements demonstrate a uniaxial magnetic anisotropy (UMA) on the coercivity (Hc), and saturation field (Hs). The ferromagnetic resonance (FMR) shows that the difference between demagnetizing fields in the direction of easy and hard increases with increasing the length-to-diameter aspect ratio of nanochains, which is close to then that in Hs. From FMR measurements and theoretical simulation, the difference of the demagnetizing field between the length and width...

Investigation of magnetization dynamics damping in Ni80Fe20/Nd-Cu bilayer at room temperature

Focusing on the Ni80Fe20 (Py)/Nd-Cu bilayers, the magnetization dynamic damping from spin pumping effect is investigated systematically by doping itinerant Cu in rear earth metal Nd. Various Ta/Py/Nd1-xCux/Ta/Si films with x = 0%, 16%, 38%, 46% and 58% are prepared by magnetron sputtering. For every content of Cu, the thickness of Nd-Cu layer is changed from 1 nm to 32 nm. The damping coefficient increases with increasing the thickness of Nd-Cu layer, which shows the trend of the spin pumping behavior. Also, with increasing Cu concentration in the Nd-Cu layer, the damping coefficient decreases, implying that the spin-orbit coupling in Nd-Cu layer is indeed cut down by high itinerant of Cu dopants. It is interesting that the spin diffusion length (λSD) in the Nd-Cu layer for different Cu dopants is not found to increase monotonously.

Magnetocrystalline anisotropy in textured Fe 3 O 4 film

The magnetic anisotropies are one of the dominating factors affecting the behavior of magnetic materials, which is profoundly evident in magnetic ultrathin films, and significant in the application of information storage and magnetic sensor field. Extensive studies of magnetic anisotropies in various films have been carried out. It is well known that the contribution of magnetocrystalline anisotropy is negligible in isotropic polycrystalline films while essential in single-crystal films. However, in textured film, a polycrystalline film composed of nanograins with the near same lattice orientation, the competing interactions between magnetocrystalline and other anisotropy is still an open issue. The quantitative investigations on the contribution of magnetocrystalline anisotropy in the textured film are rarely reported. In this paper, the expression of magnetocrystalline anisotropy energy in textured film (texture anisotropy energy) is given, and angle-resolved FMR studies on the textured Fe3O4 film is also presented.