Kurt W. Wierman

Magnetization reversal and defects in Co/Pt multilayers

(Co 3 A/Pt 10 A)×N (N=8, 16, and 30 bilayers) multilayer thin films were prepared by sputtering onto an 850‐A‐thick SiN layer that had been deposited on a silicon (111) substrate. We used the polar Kerr effect to measure the time dependence of magnetization reversal over the temperature range 90–300 K. Direct domain observations were also carried out. The results show that the domain expansion process depends strongly on the number of bilayers. Uniform domain expansion was found only in the thinner samples. From the time dependence of the magnetization reversal measurements over the temperature range 90–300 K, the activation energy and volume associated with domain wall motion were found to be 1.2 eV and 2.3×10−18 cm3 for N=8 sample. The N=16 and N=30 samples seem to have a broad distribution of activation energies. Our observations suggest that both the coercivity and magnetization reversal are controlled by the defects that come from the interface between the Co and Pt.

Magneto-optical and structural properties of nanocrystalline MnBi-based films

Abstract In this paper we discuss recent research on MnBi and MnBiX films where X denotes alloying elements whose purpose is to modify the properties of the parent compound in beneficial ways. While MnBi has a large Kerr response, large uniaxial anisotropy and can be grown in thin-film form with its easy axis normal to the film plane, it also has large grain sizes and a high-temperature structural instability near the Curie point, both of which are detrimental to magneto-optic recording applications. We report systematic studies of Al doping which show that it does not enhance the Kerr response nor eliminate the high temperature structural instability. Al does, however, promote small grain sizes which are required for a low noise magneto-optical recording medium. Preliminary results are reported on sputtered samples with a number of other dopants, and some of these have promising properties.

Long-range order and magnetic properties of MnxPt1−x thin films

Abstract Thin films of MnxPt1−x (x = 0.18, 0.22, 0.25, 0.30, 0.34) were prepared by magnetron sputtering onto quartz substrates. After annealing in vacuum for 1 h at 850°C, X-ray diffraction indicates that the films have the Cu3Au cubic structure ( a = 3.87 A ) and are highly textured with the (111) axis along the film normal. These samples have a high degree of long-range order, as indicated by the ratio of the intensities of the superlattice (100) and fundamental (200) X-ray diffraction reflections. We report here the results of magnetic and magneto-optical measurements on these samples over a wide range of temperatures.

In situ and ex situ optical characterization of electro deposited magneto-optic materials

Electrodeposition is being investigated as a novel and low‐cost method to prepare magneto‐optic thin film and nanostructured materials. This deposition method allows precise control over thin‐film properties and permits deposition of novel magnetic geometries. Multilayers and alloys can be deposited and controlled by adjusting deposition potentials and ion concentrations in the bath. Nickel/cobalt alloys have been electrodeposited from sulfamate, sulfate, and chloride solutions onto Au substrates. The optical properties were monitored in situ with a real‐time spectroscopic ellipsometer measuring simultaneously at 44 wavelengths in the 410–750 nm spectral range. In situ measurements have the advantage of determining the material microstructural properties (thickness, density, and roughness) before the films are oxidized in the air ambient. Ex situ variable angle spectroscopic ellipsometry measurements were taken over the spectral range from 205 to 1000 nm.

Low‐temperature characterization of the magnetic properties of MnBiAl thin films

The magnetic properties of thin‐film samples of MnBi0.8Alx with aluminum concentrations of x=0.0, 0.4, 0.6, and 0.8 were systematically studied over a temperature range of 20 to 300 K. The as‐deposited films are amorphous and nonmagnetic, but highly textured polycrystalline films that are ferromagnetic are formed by annealing at 350 °C. Our measurements show that the coercivity of such films rapidly decreases, then approaches a constant value (4 kOe for x=0.4) with increasing annealing time. Magnetic measurements show that both anisotropy and coercivity decrease with decreasing temperature. Unlike bulk MnBi, our MnBi0.8Alx thin films do not have a spin reorientation transition at low temperatures. This may be due to impediment of the lattice contraction by the Al atoms doped into the interstitial sites of the MnBi lattice.

Magneto‐optical and structural properties of BiAlDyIG/Fe multilayers

Bi‐ and Al‐doped DyIG(y A)/Fe(x A) (y=50 to 130 A and x=5 to 15 A) multilayer thin films were made by magnetron sputtering onto Si(111) substrates. Rapid thermal annealing was used to crystallize these garnet multilayers. The crystallized multilayer samples possess well‐defined interfaces. Atomic force microscopy showed that the annealed samples had smooth surfaces, with small grain sizes (∼30 to 80 nm). All of the samples had perpendicular magnetic anisotropy with very square hysteresis loops. The coercivity was found to vary from 600 Oe to 2 kOe, depending on Fe thickness and annealing conditions. The measured figure of merit √R(θ2K+e2K) at 420 nm was bigger than 0.4, suggesting that Bi‐ and Al‐doped DyIG/Fe multilayers are promising candidates for blue light magneto‐optical recording applications.

Magnetic and magneto-optical properties of Mn/sub x/CuBi(x=0.75-3.5) films

Magnetic and magneto-optical properties of Mn/sub x/CuBi(x=0.75-3.5) thin films are presented. With increasing Mn concentration x, the perpendicular anisotropy constant (K/sub u/), the remanence squareness (S=M/sub r//M/sub s/) and the coercivity (H/sub c/), of the perpendicular hysteresis loop increase. Remanence squareness as high as 0.95 has been obtained. Kerr rotation (/spl theta//sub k/) and ellipticity (/spl eta//sub k/) spectra from all samples measured from the substrate side are similar, with /spl theta//sub k/ exhibiting a broad peak in the blue wavelength region with maximum Kerr rotation up to 0.7 degrees.

Magnetic and magneto‐optical properties of MnxPt1−x−yZny

In this work we have prepared thin films of the ternary alloy Mn x Pt1−x−y Zn y by magnetron sputtering onto quartz substrates. We have found a wide range of compositions which are strongly ferromagnetic at room temperature. A transition from a cubic to tetragonal phase with decreasing Pt content is confirmed by x‐ray diffraction. X‐ray diffraction measurements also show a strong (001) reflection consistent with long range order along the c axis for the tetragonal phase. These films show large complex Kerr rotations (up to 0.7°) in the visible spectrum. This combined with their anisotropic structure suggests that they may be suitable for magneto‐optic data storage applications.

Magneto-optical and structural properties of DIG/T (T Fe, Co, Dy) multilayers

Abstract We investigated (Bi, Al)-doped Dy 3 Fe 5 O 12 /T (T = Fe, Co, Dy) multilayer thin films prepared by magnetron sputtering and subsequent processing by multipulse rapid thermal annealing. These multilayer garnet samples have very square hysteresis loops, large coercivity and nanoscale size grains. Large effective Kerr rotations were found in the blue wavelength region.

Optical and magneto-optical properties of MnPt3 films (abstract)

Optically thick films of MnPt3 were prepared by magnetron sputtering onto quartz substrates. Postdeposition annealing at 850 °C resulted in highly textured (111) films with the L12 (Cu3Au) structure. MnPt3 films are ferromagnetic with a Curie temperature of 380 °C, and they show large magneto-optical effects in the visible.12 These films also show a high degree of long-range order. The diagonal components of the dielectric tensor were determined using variable angle spectroscopic ellipsometry measurements over the spectral range 1.2–2.4 eV. Magneto-optic Kerr rotation and ellipticity measurements were made at near normal incidence over the spectral range 1.4–3.6 eV to determine the off-diagonal components of the MnPt3 dielectric tensor. First-principles electronic structure calculations were carried out for the ordered MnPt3 structure, and from these the components of the dielectric tensor were calculated. We find excellent agreement between the measured and calculated diagonal components, but only fair a...