Optical recording aspects of rf magnetron-sputtered iron-garnet films

Abstract

The intrinsic magneto-optical readout performance in reflection is calculated for bismuth and cobalt-substituted iron-garnet films on a multilayer interference mirror at 800-, 633-, 488-, and 420-nm wavelengths and is compared with that of a trilayer medium composed of an antireflection layer, a rare-earth transition-metal film, and a metallic mirror. It is found, when disregarding inhomogeneities, like irregular domain shape, ripple of the magnetic anisotropy, and surface roughness, that iron garnets are superior to rare-earth transition-metal films at blue to near-ultraviolet wavelengths if operated at thicknesses where optical interference occurs in the magnetic layer. Optical transmittance at these thicknesses is sufficiently high so that multilevel recording media can be conceived. In contrast, the optical absorption of rareearth transition-metal alloys is much higher so that only thicknesses much above interference conditions are feasible, thus precluding them from multilevel recording. This comparative study is supplemented by calculating the magneto-optical performance in reflection of a recently reported multilayer medium composed of an antireflection coating and a periodically repeated sandwich of 4-A Co and 9-A Pt layers. In contrast to conventional rare-earth transition-metal films, the magneto-optical Kerr effects of this material do not degrade when decreasing the wavelength from 800 to 400 nm, but still do not reach the performance of bismuth-iron garnets in the green to ultraviolet spectrum. For the garnet system Y 3 __ x Bix Fe 5 0 12 the spectra of the real and imaginary parts of the diagonal and off-diagonal component of the dielectric tensor eij are reported in the range of photon energies between 1 and 5 eV, i.e., 1240-and 248-nm wavelengths and a bismuth concentration up x = 1.4 Bi3+ atoms per garnet formula. In addition, the off-diagonal components €; 2 and €;' 2 are parametrized in terms of paramagnetic optical transitions, taking the spectra for x = 1.25 as a typical example. Furthermore, optical and magneto-optical spectra are presented for Co 2 +and CoHsubstituted iron garnets and barium hexaferrite BaFe 12 O 19 • Finally, the spectral dependence of the magneto-optical figure of merit 20p/a of (Y,Bi.):,Fe 5 0 12 and amorphous TbFe is compared. Furthermore, high-resolution transmission electron micrographs and x-ray double-crystal di:ffractograms are presented that elucidate the perfect epitaxial alignment of single-crystalline iron-garnet films and the columnar morphology of polycrystalline irongarnet films prepared by rf magnetron sputtering. The initial nucleation period of polycrystalline garnet films can be influenced by low-energy ion bombardment for i.mproving the film texture. Under favorable sputtering conditions single-and polycrystalline bismuthiron garnet films develop a perpendicular magnetic anisotopy. It is not yet clear whether sputtered iron-garnet films can meet the critical requirements on magnetic wall coercivity and magnetic remanence. 4393 J. Appl. Phys. 66 (9), 1 N...

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