Ferrochromite Films for Microwave Applications

We previously mentioned the possibility of preparing polycrystalline Mg–Mn ferrochromite films by Chemical Transport Deposition (CTD) using HCl as a reaction gas.1 The thermodynamic calculations, however, indicated that the ferrochromite chemical transport should be enchanced when using chlorine Cl2 in place of HCl. The aim of this paper is to report the effect of Cr3+ substitution on the deposition rates and on the properties of deposits grown in Cl2 containing atmosphere. The objective was to evaluate the feasibility of CTD-grown films for C- and S-band ferrite device applications. We performed our experiments using source samples belonging to the system Mg1.2Mn0.2Cru-Fe1.6−uO4 where 0≤u≤1.2. Film deposition rates were decreasing slightly with increasing u. Rates of 10 to 50 mg h−1 cm−2 were, however, achieved in the u range of interest. Typical thickness of films was 250 to 400 μ. The 4πMs of deposits was controlled by Cr3+ substitution down to zero at u=1.1 (25°C). The ΔH and tanδε were measured at X band. The dielectric losses were rather low (tanδε≅10−3) and independent on u. The ΔH was increasing with u due to increasing compositional nonuniformity. Even though minimization of this effect was not attempted, for films having 4πMs values between 2300 and 1500 G (0≤u≤0.65) the ΔH was between 220 and 350 Oe. We concluded that ferrochromite films with not too high Cr3+ content may be useful for technical applications.