Optical recording aspects of rf magnetronhyphen;sputtered ironhyphen;garnet films

摘要

The intrinsic magnetohyphen;optical readout performance in reflection is calculated for bismuth and cobalthyphen;substituted ironhyphen;garnet films on a multilayer interference mirror at 800hyphen;, 633hyphen;, 488hyphen;, and 420hyphen;nm wavelengths and is compared with that of a trilayer medium composed of an antireflection layer, a rarehyphen;earth transitionhyphen;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 rarehyphen;earth transitionhyphen;metal films at blue to nearhyphen;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 rarehyphen;earth transitionhyphen;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 magnetohyphen;optical performance in reflection of a recently reported multilayer medium composed of an antireflection coating and a periodically repeated sandwich of 4hyphen;Aring; Co and 9hyphen;Aring; Pt layers. In contrast to conventional rarehyphen;earth transitionhyphen;metal films, the magnetohyphen;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 bismuthhyphen;iron garnets in the green to ultraviolet spectrum. For the garnet system Y3minus;xBixFe5O12the spectra of the real and imaginary parts of the diagonal and offhyphen;diagonal component of the dielectric tensor egr;ijare reported in the range of photon energies between 1 and 5 eV, i.e., 1240hyphen; and 248hyphen;nm wavelengths and a bismuth concentration upx=1.4 Bi3+atoms per garnet formula. In addition, the offhyphen;diagonal components egr;rsquo;12and egr;squflg;12are parametrized in terms of paramagnetic optical transitions, taking the spectra forx=1.25 as a typical example. Furthermore, optical and magnetohyphen;optical spectra are presented for Co2+hyphen; and Co3+hyphen; substituted iron garnets and barium hexaferrite BaFe12O19.Finally, the spectral dependence of the magnetohyphen;optical figure of merit 2THgr;F/agr; of (Y,Bi)3Fe5O12and amorphous TbFe is compared. Furthermore, highhyphen;resolution transmission electron micrographs and xhyphen;ray doublehyphen;crystal diffractograms are presented that elucidate the perfect epitaxial alignment of singlehyphen;crystalline ironhyphen;garnet films and the columnar morphology of polycrystalline ironhyphen;garnet films prepared by rf magnetron sputtering. The initial nucleation period of polycrystalline garnet films can be influenced by lowhyphen;energy ion bombardment for improving the film texture. Under favorable sputtering conditions singlehyphen; and polycrystalline bismuthhyphen;iron garnet films develop a perpendicular magnetic anisotopy. It is not yet clear whether sputtered ironhyphen;garnet films can meet the critical requirements on magnetic wall coercivity and magnetic remanence.