A number of different plasma chemistries have been employed for patterning of LaCaMnO3 and SmCo thin films for application in magnetic-field-biased structures based on the-colossal magnetoresistive effect. For LaCaMnO3 there was no chemical enhancement in etch rate over simple Ar sputtering for Cl-2, SF6, and CH4/H-2 plasmas under high ion density conditions. This is expected based on the vapor pressures of the prospective etch products. For SmCo, however, etch rates up to 7000 Angstrom min(-1) were obtained in Cl-2/Ar plasmas, which is an order of magnitude faster than Ar sputtering under the same experimental conditions. Smooth etched surface morphologies and anistropic sidewalls were obtained for both materials over a wide range of plasma source and chuck powers.