In-Plane Uniaxial Magnetic Anisotropy of Cobalt Doped Y 3 Fe 5 O 12 Epitaxial Films
- PDF / 383,695 Bytes
- 6 Pages / 418.68 x 637.2 pts Page_size
- 9 Downloads / 206 Views
Strong exchange coupling has been observed for isostructural couples with comparable lattice parameters, but coupling is not observed for heterostructural couples, regardless of similarities in lattice parameter [3]. In order to investigate this two layer device design, we have recently developed a magnetically hard doped YIG thin film material to use as an exchange-bias layer for magnetically soft YIG films. It has been found in bulk that Co 31 is not as effective as Co 21 in enhancing the uniaxial magnetic anisotropy in tetrahedral, octahedral or dodecahedral sites (4), and this is found to be 2 the case in our thin films as well. Previous work in bulk has shown that the incorporation of Co 1 on the preferred octahedral site of the garnet structure will increase magnetic anisotropy [4,5]. Previous bulk work has been in the low Ge 4+/Co2+limit (up to 0.8%) where single ion theory of magnetic anisotropy is valid [5,6]. We present here our work on the fabrication and characterization of Co 2' doped YIG films with uniaxial anisotropy in the plane of the film. In order to dope the octahedral site over a significant range of Co 2+concentrations, we have charge compensated Co 21 ions with either Ce4+ or Ge 4+ ions, extending the limits of our solid solution. Previous work with polycrystalUine YIG films prepared by MOCVD, with Ce4+ and Ge4+ charge compensated Co 2+, have shown that with increasing dopant levels the Curie temperature (TJ)and saturation magnetization (Ms) decrease,
95 Mat. Res. Soc. Symp. Proc. Vol. 603 0 2000 Materials Research Society
while the coercive field (Hc) increases [7,8]. Our work is focused on enhancing the in-plane magnetic anisotropy of YIG while not reducing the M, significantly, in light of the exchange biasing role that the material should perform. EXPERIMENT Synthesis We have chosen as our substrate (110) oriented Gd 3Ga 5O 12 (GGG) for several reasons. The substrate and film both have the garnet structure. The lattice parameter of GGG, 12.376A is comparable to the 12.380A lattice parameter of undoped YIG. Most work with YIG on GGG for magneto-optical storage applications have been with (111) oriented substrates, but this orientation counters our objective, as growth induced anisotropy results in an easy axis along the film normal. The (110) film orientation is ideal for our study, as we can study the magnetization along the (100), (110), and (111) directions, all in the plane of the film. The films are deposited using the pulsed-laser deposition technique. Targets are prepared from stoichiometric amounts of Y20 3, Fe 20 3, Co(N0 3)2*6H 20, GeO 2, and CeO 2. The mixed powders are heated in air for 12 hours at 600'C, ground and pressed into cylindrical pellets 1"in diameter. The pellets are placed on powders of their own composition and fired at 1050'C in air for 60 hours. Single phase polycrystalline targets are successfully prepared for Y3Fe5 .2xCoxGexO1 2 (x=0, 0.25, 0.5) and Y3.xCexFe5_.CoO,12 (x=0.25, 0.5, 0.75). The films are deposited at 600'C in l0mTorr 02. We use a KrF excimer
Data Loading...
