Structure and magnetic properties of yttrium-iron-garnet thin films prepared by laser deposition

We report on a study of thin (500-4000 Angstrom) and ultrathin (100-500 Ang strom) yttrium-iron-garnet (YIG) films deposited onto amorphous quartz subs trates by the pulsed laser deposition technique. The growth conditions of w ell-formed polycrystalline films have been determined. The crystalline stru cture and the magnetic behavior of the films are strongly influenced by the processes occurring on the film-substrate interface. Primarily, a strain d ue to the difference in thermal expansion coefficients of the film and subs trate induces a uniaxial anisotropy. Another source of strain are lattice d istortions due to oxygen vacancies. The results obtained from x-ray diffrac tion analysis, magneto-optical, superconducting quantum interference device , vibrating sample magnetometer, and ferromagnetic resonance (FMR) measurem ents indicate that films thicker than 200 Angstrom can be approximated by a two-layer model. One of the layers with a highly distorted structure and l ow magnetization is located near the surface. The other one, the upper laye r, can be estimated as an almost perfectly formed YIG. Their relative thick ness determines the magnetic and FMR behavior of the samples. An equilibriu m direction of the magnetization along the film normal has been found to oc cur in the ultrathin films with the lowest magnetization where the perpendi cular anisotropy energy exceeds the dipolar energy. (C) 2001 American Insti tute of Physics.