Optimized pulsed laser deposited barium ferrite thin films with narrow ferromagnetic resonance linewidths

Hexagonal M-type barium ferrite (BaM) films have been prepared by pulsed laser deposition. Optimal preparation conditions gave pure single phase films with the narrowest possible ferromagnetic resonance (FMR) linewidths. The films were deposited on c-plane sapphire substrates with a KrF excimer laser at wavelength of 248 nm and fluence of 1.7 J/cm(2). The minimum linewidth films were obtained for an oxygen partial pressure of 300 mTorr and a substrate temperature of 910 degreesC, and were 0.85 mum thick. X-ray diffraction indicated pure single crystal BaM phase with local c-axis deviations less than 0.15degrees. Vibrating sample magnetometry data gave hysteresis loops with minimal hysteresis and small coercive force, saturation induction 4piM(s) of 4.2 kG and uniaxial anisotropy field H-A of 16.4 kOe. The H-A matches the anisotropy for bulk and the 4piM(s) is about 10% below literature values for the bulk. The FMR spectra were measured from 50 to 75 GHz by shorted wave guide techniques with the static field perpendicular to the film. The optimized film uniform mode half power FMR linewidth at 60.3 GHz was 27 Oe. This linewidth was a linear function of the frequency with a response coefficient of 0.5 Oe/GHz and nearly zero frequency intercept. Within experimental error, this linewidth response is the same as for bulk crystals. The FMR spectra show additional standing spin wave (SSW) resonances which could be indexed to give field positions that scale with the square of index n except for low order modes. The scaling gave a standard exchange energy parameter, A(ex), of 6.4x10(-7) erg/cm. The SSW linewidths scaled with n(2). Application of the Kittel thickness variation model to the SSW linewidth data gave an estimated thickness variation of the film of about 7%. (C) 2003 American Institute of Physics.