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The effects of a negative bias voltage during film preparation on both the magnetic properties and microstructure of Co92Zr8 (at%) films deposited by rf magnetron sputtering have been investigated. A low coercive force Hc and high permeability μ are obtained when negative bias voltages lower than -75 V are applied. Values of the magnetostriction constant λs for bias-sputtered films are smaller than those for unbiased films. The μ value for bias- sputtered films after 1000 hours of heat treatment at 80°C decreases to approximately 80% of its initial value, while a decrease of about 40% is observed for unbiased films. The decrease in λs values and the improvement in stability of the permeability can be explained in terms of the structural difference between films sputtered with and without a bias voltage applied. It is concluded that bias-sputtered films with a negative bias voltage below -75 V are excellent candidates for use as thin film head pole pieces.