The effect of Ta buffer layer in IrMn top spinvalve using high vacuum DC magnetron sputtering was investigated. An optimized thickness (3 nm) of the Ta buffer layer was proposed. With the 3 nm thick Ta buffer layer, high magnetoresistance ratios of 9.24%, an exchange bias field of 255 x (10(3)/4pi) A/m and a coercivity of 2.43 x (10(3)/4pi) A/m were obtained. These spinvalve structures can be the promising candidate of the robust giant magnetoresistance sensors for automobile and industrial-control system applications. (C) 2003 Elsevier B.V. All rights reserved.