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Thin films (≊0.4 μm) of cobalt ferrite (CoFe2O4) have been grown on single-crystal (100) MgO substrates using pulsed laser deposition (PLD). The phase, orientation, and microstructure of the as-deposited films were investigated as a function of substrate temperature (i.e., 200–800 °C) at a constant oxygen deposition pressure of 30 mTorr. The as-deposited films were found to be single phase, well oriented, and approximately matching the stoichiometry of the target, but the cubic lattice constant of the films depended on the substrate temperature indicating that the films were strained. The greatest effect of the substrate temperature was on the magnetic properties of the as-deposited films. At 800 °C, 4πMs was measured to be 5370 G which is approximately the accepted bulk value for cobalt ferrite. In addition, PLD cobalt ferrite films grown at substrate temperatures of 600 and 800 °C exhibited a uniaxial magnetic anisotropy with an easy direction normal to the film plane. Films grown at 200 and 400 °C also exhibited a uniaxial magnetic anisotropy but possessed a planar easy direction.

Variable frequency ferromagnetic resonance (FMR) has been used to directly observe the coupled resonance modes in single-crystal Fe/Cr/Fe(001) sandwiches grown by molecular-beam epitaxy. Magnetization M and magnetoresistance measurements also were carried out on these samples, which exhibited antif erromagnetic (AF) layer alignment for 12

Epitaxial thin films of barium hexaferrite (BaFe12O19) have been fabricated by the pulsed laser deposition technique on basal plane sapphire. Structural studies reveal the films to be predominantly single phase and crystalline, with the c axis oriented perpendicular to the film plane. The magnetic parameters deduced from vibrating sample magnetometer and ferromagnetic resonance (FMR) measurements are close to the parameters associated with bulk materials. Post annealing of the films reduced the FMR linewidth by more than a factor of 3 so that it compares reasonably well with single-crystal films. The derivative FMR linewidth was measured to be 66 Oe at 58 GHz and 54 Oe at 86 GHz. Spin-wave-like modes have been observed for the first time in barium ferrite films. The deduced exchange stiffness constant of 0.5×10−6 ergs/cm is in reasonable agreement with recent calculations.

The pyrite Fe1−xCoxS2 (0.25⩽x⩽0.9) was predicted to be half metal, insensitive to Fe–Co disorder. To verify its half metallicity, we have grown single crystals of Fe1−xCoxS2 (x=0.35, 0.5, 0.75, 0.9, and 1). Crystals of up to a few mm in size by temperature gradient (923–873 K) solution growth from Te melts, which showed high crystalline quality by scanning electron microscopy, x-ray diffraction, and magnetic measurements. A half-metallic magnetization of 1±0.03μB per Co atom was found for x=0.35–0.9. Point contact Andreev reflection measurements, however, showed spin polarization of 47%–61% with the maximum around x=0.5, well below predictions. Ferromagnetic resonance measurements give g∼2.08 with large intrinsic damping, which indicates a reduced half-metallicity. Inductively coupled plasma and energy dispersive x-ray spectroscopy results confirm a sulfur deficiency of ∼1.5%–10% [(Fe,Co)S2−y,0.03⩽y⩽0.2] and small amounts of Te. Electronic structure calculations show the extra electron provided by Co substitution to FeS2 populates a sulfur-derived conduction band. Consequently, S deficiency and/or S site disorder are expected to affect the transport properties. This is consistent with the low polarization measurements and again indicates the importance of crystalline order in obtaining highly spin-polarized materials.