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  1. Abstract This work focuses on the nature of magnetic anisotropy in 2.5–16 micron thick films of nickel ferrite (NFO) grown by liquid phase epitaxy (LPE). The technique, ideal for rapid growth of epitaxial oxide films, was utilized for films on (100) and (110) substrates of magnesium gallate (MGO). The motivation was to investigate the dependence of the growth induced anisotropy field on film thickness since submicron films of NFO were reported to show a very high anisotropy. The films grown at 850–875 C and subsequently annealed at 1000 C were found to be epitaxial, with the out-of-plane lattice constant showing unanticipated decrease with increasing film thickness and the estimated in-plane lattice constant increasing with the film thickness. The uniaxial anisotropy field H σ , estimated from X-ray diffraction data, ranged from 2.8–7.7 kOe with the films on (100) MGO having a higher H σ value than for the films on (110) MGO. Ferromagnetic resonance (FMR) measurements for in-plane and out-of-plane static magnetic field were utilized to determine both the magnetocrystalline the anisotropy field H 4 and the uniaxial anisotropy field H a . Values of H 4 range from −0.24 to −0.86 kOe. The uniaxial anisotropy field H a was an order of magnitude smaller than H σ and it decreased with increasing film thickness for NFO films on (100) MGO, but H a increased with film thickness for films on (110) MGO substrates. These observations indicate that the origin of the induced anisotropy could be attributed to several factors including (i) strain due to mismatch in the film-substrate lattice constants, (ii) possible variations in the bond lengths and bond angles in NFO during the growth process, and (iii) the strain arising from mismatch in the thermal expansion coefficients of the film and the substrate due to the high growth and annealing temperatures involved in the LPE technique. The LPE films of NFO on MGO substrates studied in this work are of interest for use in high frequency devices. 
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  2. This report is on the nature of strain in thin films of yttrium iron garnet (YIG) on yttrium aluminum garnet (YAG) substrates due to film-substrate lattice mismatch and the resulting induced magnetic anisotropy. Films with thickness 55 nm to 380 nm were deposited on (100), (110), and (111) YAG substrates using pulsed laser deposition (PLD) techniques and characterized by structural and magnetic characterization techniques. The in-plane strain determined to be compressive using X-ray diffraction (XRD). It varied from −0.12% to −0.98% and increased in magnitude with increasing film thickness and was relatively large in films on (100) YAG. The out-of-plane strain was tensile and also increased with increasing film thickness. The estimated strain-induced magnetic anisotropy field, found from XRD data, was out of plane; its value increased with film thickness and ranged from 0.47 kOe to 3.96 kOe. Ferromagnetic resonance (FMR) measurements at 5 to 21 GHz also revealed the presence of a perpendicular magnetic anisotropy that decreased with increasing film thickness and its values were smaller than values obtained from XRD data. The PLD YIG films on YAG substrates exhibiting a perpendicular anisotropy field have the potential for use in self-biased sensors and high-frequency devices. 
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  3. A model for the low-frequency magnetoelectric (ME) effect that takes into consideration the bending deformation in a ferromagnetic and ferroelectric bilayer is presented. Past models, in general, ignored the influence of bending deformation. Based on the solution of the equations of the elastic theory and electrostatics, expressions for the ME voltage coefficients (MEVCs) and ME sensitivity coefficients (MESCs) in terms of the physical parameters of the materials and the geometric characteristic of the structure were obtained. Contributions from both bending and planar deformations were considered. The theory was applied to composites of PZT and Ni with negative magnetostriction, and Permendur, or Metglas, both with positive magnetostriction. Estimates of MEVCs and MESCs indicate that the contribution from bending deformation is significant but smaller than the contribution from planar deformations, leading to a reduction in the net ME coefficients in all the three bilayer systems. 
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