Effect of Ta seed layer on crystalline structure and magnetic properties in an exchange-biased Co/IrMn system

Ta-seeded and un-seeded layers of a top-configuration Co/IrMn system were deposited onto glass substrate by DC sputtering. Three sets of deposition conditions for Co(50 A)/IrMn( t IrMn A) and Co( t Co A)/IrMn(90 A), where t IrMn = 15, 30, 60, 90, 110, and 150 A, and t Co = 15, 25, 50, 75, 100, 125, and 150 A, were: condition (a) substrate temperature ( T s ) was kept at room temperature (RT). Condition (b) T s set to RT, with in-plane magnetic field, H = 500 Oe. In condition (c), condition (b) was followed by post-deposition annealing in the magnetic field at T A = 250 °C for 1 h, then field cooled to RT. X-ray diffraction (XRD) patterns and grazing incidence scans revealed maximum IrMn (1 1 1) texture to occur for post-deposition annealed Ta seed layer samples. The IrMn (1 1 1) texture-effect significantly influences magnetic properties, including exchange-biasing field ( H ex ), interfacial energy ( J k ), and coercivity ( H c ). The Ta seed layer also significantly influences magnetic properties. Adding a Ta seed layer to the Co/IrMn system increases H ex , because of the IrMn (1 1 1) texture. For Ta-seeded Co/IrMn under condition (c), H ex tended to saturate for t IrMn ≥ 90 A. Under conditions (a) and (b), H ex decreased with increasing t IrMn for t IrMn ≥ 90 A. H ex values for all un-seeded Co/IrMn systems increased with t IrMn . J k versus t IrMn plot is proportional only to H ex in the Ta-seeded and un-seeded layers of a top-configuration Co/IrMn system, due to the interfacial energy formula, t Co is fixed, and saturation magnetization ( M s ) of the Co layer is constant. Results for the Ta-seeded system showed a strong relationship between H c and t IrMn , due to coupling-decoupling interactions between Co spin, and IrMn layers close to the Co/IrMn interface. The H ex versus t Co result shows that the H ex is proportional to (1/ t Co ). The H ex values with the Ta seed layer are almost slightly larger than those without a Ta seed-layer. The dependence of J k on t Co is similar to the trend in M s on t Co , J k tends to saturate slowly as t Co increases. Surface pinning occurred in all systems, revealing an inverse relation between H c and t Co . Removing the Ta seed-layer weakens IrMn (1 1 1) texturing, reducing H ex . The maximum observed H ex and J k values were 205 Oe and 0.11 erg/cm 2 , respectively.