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 Å)/IrMn(tIrMn Å) and Co(tCo Å)/IrMn(90 Å), where tIrMn = 15, 30, 60, 90, 110, and 150 Å, and tCo = 15, 25, 50, 75, 100, 125, and 150  Å, were: condition (a) substrate temperature (Ts) was kept at room temperature (RT). Condition (b) Ts 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 TA = 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 (Hex), interfacial energy (Jk), and coercivity (Hc). The Ta seed layer also significantly influences magnetic properties. Adding a Ta seed layer to the Co/IrMn system increases Hex, because of the IrMn (1 1 1) texture. For Ta-seeded Co/IrMn under condition (c), Hex tended to saturate for tIrMn ≥ 90 Å. Under conditions (a) and (b), Hex decreased with increasing tIrMn for tIrMn ≥ 90 Å. Hex values for all un-seeded Co/IrMn systems increased with tIrMn. Jk versus tIrMn plot is proportional only to Hex in the Ta-seeded and un-seeded layers of a top-configuration Co/IrMn system, due to the interfacial energy formula, tCo is fixed, and saturation magnetization (Ms) of the Co layer is constant. Results for the Ta-seeded system showed a strong relationship between Hc and tIrMn, due to coupling-decoupling interactions between Co spin, and IrMn layers close to the Co/IrMn interface. The Hex versus tCo result shows that the Hex is proportional to (1/tCo). The Hex values with the Ta seed layer are almost slightly larger than those without a Ta seed-layer. The dependence of Jk on tCo is similar to the trend in Ms on tCo, Jk tends to saturate slowly as tCo increases. Surface pinning occurred in all systems, revealing an inverse relation between Hc and tCo. Removing the Ta seed-layer weakens IrMn (1 1 1) texturing, reducing Hex. The maximum observed Hex and Jk values were 205 Oe and 0.11 erg/cm2, respectively.

► X-ray diffraction (XRD) patterns and grazing incidence scans revealed maximum IrMn (1 1 1) texture. ► The maximum IrMn (1 1 1) texture occurs in post-deposition annealed Ta seed layer samples. ► The IrMn (1 1 1) texture-effect significantly influences magnetic properties. ► The magnetic properties include exchange-biasing field (Hex), interfacial energy (Jk), and coercivity (Hc).