X.Y. Yu

Structural anisotropy of Tb/Fe multilayers

We have investigated the local structural anisotropy of Tb/Fe multilayers using linear polarized synchrotron radiation. X‐ray absorption measurements were performed at Fe K edge (7.1 keV) using normal and glancing angle incident photon. From the Fe extended x‐ray absorption fine structure (EXAFS), the local structural anisotropy was found for all multilayers as a slight difference of oscillation amplitude between the two incident directions. From the Fourier transformed EXAFS spectra, it is found that the local structural anisotropy shows the maximum at bilayer period of about 1 nm, where perpendicular magnetic anisotropy also shows the maximum value in various rare‐earth/transition metal multilayers.

Structural and Magnetic Anisotropy of Tb/Fe Multilayers

Local structural anisotropy of Tb/Fe multilayers (MLs) was investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy. Quantitative analysis of Fe EXAFS signals was performed to estimate the coordination number related to the structural anisotropy. A difference in the Fourier-transformed Fe EXAFS spectra between two incident polarized light directions has indicated that considerable anisotropy of atomic pair ordering exists in the MLs prepared by sputtering. It was further found that the variation of the structural anisotropy well corresponds to the magnitude of the perpendicular magnetic anisotropy, which changes depending on the bilayer periods and the preparation condition.

Magnetic and magnetooptic properties of NdGd/FeCo multilayers

Abstract Magnetic and magnetooptic properties have been investigated for NdGd/Fe and NdGd/FeCo multilayers prepared by rf sputtering method. At a bilayer period of 10 to 15A, perpendicular magnetic anisotropy showed the maximum value of about 2.5 × 10 6 erg/cm 3 . Magnetooptic Kerr rotation of the multilayers reach 0.33° at 400 nm, reflecting the contribution of Nd.

Magneto-optical kerr effect of rare earth-transition metal amorphous alloy and multilayer films

Abstract Magneto-optical Kerr rotation θK spectra are shown for the amorphous alloy films of R0.30(Fe0.89Co0.11)0.70 with R = La, Pr, Nd, Sm, Eu, Gd, Tb, and Dy, and they are compared with those for R~0.20Co~0.8 films. On the whole, one of the most remarkable differences is that θK greatly depends on the species of R for a series of RFeCo in infrared regions, while θK for RCo scarcely depends on R. This difference is explained by a change in Curie temperature with the R species. Based on this model, spectral subnetwork contributions of R to θK are estimated. In ultraviolet regions, large negative contributions can be expected for R = Pr, smaller negative ones for Nd and Gd, with large positive ones for R = Tb and Dy, and almost zero for R = Sm. Although experiments are done only on a restricted number of films, the Kerr spectra change only slightly for multilayers from alloy films with corresponding compositions.

Simulation of structural anisotropy in rare-earth transition metal multilayers

Uniaxial structural anisotropy in rare-earth transition-metal amorphous multilayers has been simulated by using a close-packed superlattice as an initial condition and solving a one-dimensional diffusion equation. The simulation has revealed that the degree of the short-range anisotropic atomic order becomes the maximum at a certain bilayer period depending on the degree of the interlayer diffusion. The calculated trend of the structural anisotropy agrees with the experimental one obtained by extended X-ray absorption fine structure spectroscopy.

Dependence of magneto-optical effect of NdGd/FeCo multilayers on bilayer periods

Magneto-optical spectra have been investigated for NdGd/FeCo multilayers prepared by RF sputtering method. When the bilayer period of the multilayers is decreased, Kerr rotation at high energy becomes larger. These changes in the spectral shape at high energies can be attributed to relatively weak exchange interaction between Nd and FeCo.

Thermal stability of NdGd/FeCo multilayers

Thermal stability has been investigated for the structure and the perpendicular anisotropy Ku of Nd44Gd56/Fe89Co11 multilayer films with the bilayer period of 1 nm, where Ku becomes the maximum. From the results of isothermal annealing at temperature Ta, it has been found that the saturation magnetization Ms scarcely changes up to Ta=400 °C, while Ku is almost constant up to Ta=200 °C but decreases rather quickly for Ta above 200 °C. The decrease in Ku for Ta≳260 °C is accompanied by the decrease in the peak intensity of low angle x‐ray diffraction, namely by the deterioration of the layered structure.

Magnetic and magneto‐optical properties of (Tb,Dy)Nd/FeCo multilayers (abstract)

Nd‐Co and Nd‐FeCo amorphous films are known to have larger Kerr rotation θk at shorter wavelength and ultraviolet light compared with other RE‐TM (rare earth‐transition) amorphous films. This property is desirable for MO (magneto‐optical) media for the next generation. In order to satisfy the perpendicular magnetization condition, we replaced a part of Nd by Gd to decrease the saturation magnetization Ms and applied the multilayer (ML) structure to enhance the perpendicular anisotropy Ku. Then we succeeded in getting a new ML medium of Nd0.34Gd0.66/Fe0.9Co0.1 with a bilayer period of 1 nm. However, the substitution of 66% Gd resulted in undesirable decreases of Kerr rotation and coercivity. In this experiment, a part of Nd is replaced by either Tb or Dy instead of Gd with an expectation that the amount of replacement to get the perpendicular magnetization configuration may be smaller since Tb and Dy have large one ion anisotropy compared with Gd. The magnetic and MO properties of Nd(Tb,Dy)/FeCo MLs will b...

MAGNETO-OPTIC KERR ROTATION OF RARE EARTH-IRON BASED ALLOYS

Thin films RF30(Fe99Co11)70 (RE=Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er and Tm) were prepared by RF diode sputtering on fused quartz substrates. The spectra of Kerr rotation angle and ellipticity were measured by the polarized angle modulation method from the side of the substrate at room temperature. The strength of the magnetization and the magneto-optical Kerr effect are closely related to the Curie temperature. The Curie temperature is highest for Gd which has the maximum spin among the REs. The spectral shape of the Kerr rotation shows that the Nd, Pr contribution are of opposite sign on comparing with those of Tb, Dy at higher energies.

Spectra of the conductivity tensor of rare earth-transition metal alloy films

The Kerr rotation, θk, ellipticity, ŋk, refractive index, n, and extinction coefficient, k, were established for the amorphous Nd20(NixCo100-x)80 and Y20(NixCo100-x)80 thin film systems for 0 ≤x≤73 and in the photon energy range of 1.3 - 4.5 eV. These data were used to obtain the relevant spectra of the conductivity tensor, particularly its imaginary off-diagonal component, ωσ xy. The origin and effect of Nd and Ni upon ωσ xy (and hence also uponθk) were considered and discussed.