Structural and magnetic properties of ion-beam deposited NiFe/Co-oxide bilayers

Abstract

The structural and magnetic properties of NiFe/Co-oxide bilayers were studied. XRD investigation indicates the NiFe (Permalloy) layers (a= 3.53 A) grow with a (111) preferred orientation. The Co-oxide layers were fabricated with oxygen content in the deposition assist beam ranging from 8% (rock-salt CoO, a= 4.27 A) to 34% (spinel Co3O4, a= 8.21 A). Both the coercivity Hc and exchange bias field Hex closely follow an inverse NiFe thickness relationship. A strong temperature dependence of Hc and Hex is found in these NiFe/Co-oxide bilayers. At T= 289 K, the NiFe/CoO film exhibits an enhanced Hc relative to pure NiFe/Co or NiFe/Co3O4 bilayers, an indication of exchange coupling between the NiFe and CoO phases. At T= 10 K, the NiFe/Co3O4 film exhibits an exchange-bias loop shift of Hex∼- 200 Oe that persists to temperatures greater than 30 K (the Neel temperature of bulk Co3O4). The transition temperature of the Co3O4 film component has increased above the bulk value via exchange coupling with the permalloy. Results indicate that the exchange coupling interaction between FM and AFM layers are responsible for both enhanced coercivity and cross-tie domains.