Saturation Kerr Rotation Research Articles

Photoinduced magnetic softening of perpendicularly magnetized L1-FePt granular films

Ultrafast spin dynamics has for the first time been studied in perpendicular magnetized granular films. For FePt continuous films and FePt–MgO and FePt–Ag granular films with femtosecond laser excitations, the coercivity HC and the saturation Kerr rotation θKS are dramatically reduced, accompanied by a sharp increase in the reflectivity R. Afterward, these physical quantities are slowly recovered. The changes in HC, θKS, and R are all different among FePt, FePt–MgO, and FePt–Ag films. The difference is caused by different film thicknesses and in particular by the surface plasmon resonance of metallic nanoparticles.

Room-temperature magneto-optical activity of InMnAs thin films

Room-temperature magneto-optical activity of In1−xMnxAs heteroepitaxial thin films grown on InAs (001) and GaAs (001) substrates has been studied using the longitudinal magneto-optical Kerr effect. For single-phase layers grown on InAs and GaAs with x ranging from 0.03 to 0.09, square hysteresis loops that indicate ferromagnetic order were observed. The magnitude of the saturation Kerr rotation of all the InMnAs samples ranged from 0.29to1.1mdeg, and scaled with the manganese concentration. The shape of the hysteresis curves for samples of InMnAs grown GaAs was invariant with respect to rotation about the sample normal, indicating in-plane magnetic isotropy. In contrast, InMnAs layers on InAs exhibited strong uniaxial in-plane anisotropy with the easy axis of magnetization along the [110] and [1¯1¯0] directions. The magnetic anisotropy is attributed to the effect of epitaxial strain.

Concurrent variation of giant magnetoresistance and saturation Kerr rotation in NiCo/Cu multilayers

The dependences of magneto-optical effect, effective optical constants, and giant magnetoresistance (GMR) on the thickness of Cu layers were investigated in NiCo/Cu multilayers prepared by rf magnetron sputtering. A peak of saturation polar Kerr rotation θK, occurred simultaneously with that of GMR ratio when the Cu thickness is around 1.0 nm, where a clear drop of the effective optical constants n and k appeared. The peak of θK is mainly caused by the reduction of the effective optical constants, which dominate over the small drop of the effective off-diagonal elements of the dielectric tensor. The concurrent variation of GMR and θK is related to antiferromagnetic interlayer coupling, which may change the electron band structure and thus the optical and magneto-optical transitions of electrons.

KERR ROTATION CONSTANT IN RARE EARTH-TRANSITION METAL AMORPHOUS FILMS

The magnetization and the Kerr rotation of Gd-, Dy- and Pr-Co amorphous films with various composition are measured. Based on the molecular field theory, the temperature dependence of the saturation magnetization is analyzed, and the subnetwork magnetizations are calculated. Assuming that the saturation Kerr rotation consists of two parts, each of which is proportional to the corresponding subnetwork magnetization, the proportional constants called Kerr rotation constants are determined from the compositional dependence of the Kerr rotation. The Kerr rotation constants for Co, Gd, and Dy are about −0.2, 0, and 0.08 [deg/T], respectively, and they depend only slightly on the wavelength between 400 [nm] and 1000 [nm]. The constant for Pr, on the other hand, increases quickly with increasing wavelength from a value of −1.4 [deg/T] at 400 [nm] to −0.3 [deg/T] at 1000 [nm].

Synthesis and magnetic properties of Ni–Al2O3 thin films

Ni–Al 2 O 3 nanocomposite thin films have been produced on sapphire, silicon, and silica substrates by a combination of sol-gel processing and partial reduction reactions. Transmission electron microscopy shows Ni particles, ∼20 nm in diameter, embedded in slightly larger diameter alumina grains. X-ray diffraction lattice parameter measurements suggest that the Ni is in a state of nonhydrostatic strain. Magneto-optical Kerr effect measurements indicate that the Ni particles in the films on the silicon and silica substrates support perpendicular magnetization. The saturation Kerr rotation increases linearly with film thickness to values above pure Ni and independent of reflectivity, indicating that the material is behaving as a Faraday rotator. The enhanced magnetic properties of the composite films are related to the nonhydrostatic strain developed in the Ni particles during fabrication. It is argued that the strains originate from the coefficient of thermal expansion mismatch between the film and substrate, and likely the volume shrinkage associated with the reduction reaction.

Perpendicular magnetic anisotropy and magneto-optical Kerr rotation in FePt(001) monoatomic multilayers

[Fe(1 ML)/Pt(1 ML)] (001) monoatomic multilayers, equivalent to the L1 0 ordered phase, have been prepared by depositing alternate monoatomic layers of Fe and Pt. The surface flatness and the degree of layer ordering improve with increasing substrate temperature. The perpendicular magnetic anisotropy and Kerr rotation (λ = 633 nm) at room temperature increase with increasing degree of layer ordering. The highly ordered Fe/Pt monoatomic multilayers grown at 500°C show a very large perpendicular anisotropy, which is close to the magnetocrystalline anisotropy of FePt(L1 0) ordered alloy, and a high saturation Kerr rotation of 0.69°.

Annealing Effects on Magnetic Properties of Co/Pt Multilayers

Co/Pt multilayer films sputter-deposited with and without a substrate bias of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> =-30 V were annealed in vacuum at 300 and 400°C. On annealing the saturation magnetization M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> and the saturation Kerr rotation angle θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</sub> both increased, while the perpendicular anisotropy energy K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> decreased monotonically. The decrease in K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> was larger for -30 V biased films than for 0 V films because of the larger decrease in the surface anisotropy K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> for -30 V biased films. This larger decrease in K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> is discussed taking the relaxation of lattice strain due to annealing into account.

NdFeCo TRILAYER AMORPHOUS FILMS WITH HIGH KERR ROTATION AT SHORT WAVELENGTHS

Magneto-optical recording materials with high remanent Kerr rotation at short wavelengths were successfully obtained in a trilayer form. A NdFeCo amorphous film with in-plane magnetization, but with a large saturation Kerr rotation angle at short wavelengths, was sandwiched between TbFeCo amorphous films with strong perpendicular anisotropy and high coercivity. The trilayer film, Tb20Fe74Co6 (10 nm)/Nd16Fe57Co27 (7.5 nm)/Tb20Fe74Co6 (100 nm), shows a remanent Kerr rotation angle θKr = 0.32° at a wavelength of 400 nm, coercivity Hc = 2.4kOe, and a good square loop (θKr/θKs ∼ 1).

ANNEALING EFFECTS ON THE CRYSTALLOGRAPHIC AND MAGNETIC PROPERTIES OF Co/Pt MULTILAYERS

Co/Pt multilayers with thickness ratio dCo/dPt = 1/1 have been annealed in vacuum at 300°C, 400°C and 500°C. With annealing, the saturation magnetization Ms and the saturation Kerr rotation angle increase and approach the values of alloyed films. On the other hand, the perpendicular anisotropy energy decreases monotonically owing to both the reduction of the interfacial anisotropy energy and the increase of the demagnetizing energy 2πMs2. These changes in the magnetic properties are explained by the alloying at the layer boundaries due to annealing. The diffusion process is analyzed by means of X-ray diffraction method and is suggested to be connected with the boundary diffusion. The change in the composition profiles in the double layered films of 1000ACo/1000APt has been examined by Rutherford Backscattering Spectroscopy. The RBS data also indicate that Co and Pt atoms migrate through the grain boundaries and the column boundaries.

Kerr effect study of hydrogen implanted bubble garnet films

Thin films of (YSmLuCa)/sub 3/(FeGe)/sub 5/O/sub 12/ garnet implanted with 1.5*10/sup 16/ II/sup +//sub 2/ cm/sup -2/ at 60 keV have been studied using the polar Kerr effect. Saturation Kerr rotation theta /sub k/, which is related to garnet sublattice magnetizations and Kerr rotation saturation field H/sub perpendicular to / corresponding to the effective anisotropy field induced by the implantation were measured at room temperature. The profiles of theta /sub k/ and H/sub perpendicular to //sup s/ vs. depth of the hydrogen-implanted layer for different annealing temperatures are presented and discussed. >

Preparation of amorphous Tb-Fe-Co thin films by plasma-free high-rate sputtering

The facing targets type of sputtering (FTS) apparatus [Naoe, Yamanaka, and Hoshi, IEEE Trans. Magn. MAG-16, 646 (1986)] can prepare amorphous Tb-Fe-Co thin films on plasma-free substrates at temperatures lower than 100 °C at a deposition rate as high as 5000 Å/min. The saturation Kerr rotation at 830 nm, reflectance and coercive force of the specimen films 1000 Å thick were 0.3, 48%, and 6 kOe, respectively, comparable to those obtained in films deposited at a one-hundredth lower rate by conventional rf diode and dc magnetron sputtering. Films with good uniformity of thickness, composition, and characteristics were deposited over the whole area of 12-in. disk substrates made of PMMA or glass, without deteriorating the pregrooves. At this stage, a C/N of about 46 dB has been attained.

Kerr and Hall Effects in GdEuCo Sputtered Films

The Kerr rotation angle and Hall effect in GdEuCo sputtered films are discussed. The results indicate that the absolute values of the saturation Kerr rotation angle (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sup> ) varied somewhat at the center and ends of the substrate samples, but these values were maximum around 2 percent Eu. θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sup> decreased uniformly above 2 percent Eu. The Hall voltage at saturation magnetization (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sup> ) reaches a minimum at around 3 percent Eu and then increases, exceeding the value found at 0 percent Eu and exhibits a movement opposite to the Kerr effect. Adding Eu causes either a uniform decrease in Co, or an increase in RE, but there is no such uniform increase or decrease in V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sup> .

Lateral homogeneity test of CoCr disks using the Kerr magneto-optical effect

Lateral homogeneity of the magnetic properties of a CoCr layer sputtered on a disk may be a problem. By using the Kerr magneto-optical effect the lateral homogeneity of a disk can be measured without destroying the disk. An apparatus is described which measures the magneto-optical hysteres is loop at a certain number of spots forming a grid on the disk. For each hysteresis loop, representing the properties of an area with about 1 mm in diameter, the magnetic parameters relevant for vertical magnetic recording are determined by using fitting procedures. The parameters are coercivity, saturation Kerr rotation and squareness. The calculations are performed by the computer controlling the apparatus. After all spots have been measured, the computer calculates and draws a picture of the lateral dependence of each parameter. The results of inhomageneous disks are compared with results from write/read tests on the same disks. Azimuthal and radial variations in the output voltage can be attributed to local inhomogeneities in coercivity or squareness.

Magnetic Kerr Rotation and Sublattice Iron Moment in Gd-Fe Amorphous Alloy Films

We investigated longitudinal Kerr loops vs composition on Gd-Fe alloy films and confirmed that Kerr rotation in these films was due mostly to the transition metal. The sublattice moment (from the saturation Kerr rotation angle) of iron in GdFe alloy films first increased slightly and suddenly decreased at 10 atomic% GdFe and finally decreased monotonically with decreasing iron content. The effect of this zigzag variation in the sublattice iron moment could be observed in the compositional dependence of the saturation magnetization.