Using a zero-magnetization ferromagnet as the pinning layer in exchange-bias systems

Exchange bias properties have been investigated in a (Sm_1-xGd_xAl₂/SmAl₂) bilayer (for x=0.028 ) with perpendicular magnetization, an original exchange-coupled system based on the zero magnetization ferromagnet (Sm_1-xGd_xAl₂) as the pinning layer. This unusual magnet exhibits a magnetic compensation temperature where it presents both a zero magnetization and a long-range spin ferromagnetic order. In the (Sm_1-0.028Gd_0.028Al₂/SmAl₂) bilayer, a large positive exchange bias has been observed for the SmAl₂ magnetization reversal, attesting for the exchange coupling between both compounds, even at the Sm_1-0.028Gd_0.028Al₂ magnetic compensation temperature; the magnetization of the Sm_1-0.028Gd_0.028Al₂ part of the bilayer appears to be pinned but the pinned component is obviously smaller than the one observed in a single uncovered Sm_1-0.028Gd_0.028Al₂ . X-ray Magnetic Circular Dichroïsm experiments have been undertaken to investigate the magnetization reversal in both layers independently and more particularly to probe the Sm_1-0.028Gd_0.028Al₂ behavior in its zero-magnetization state. They reveal that approximately 20% of the Sm_1-0.028Gd_0.028Al₂ layer is driven to reverse by exchange coupling to SmAl₂ . The presence of lateral domains in the Sm_1-0.028Gd_0.028Al₂ layer likely accounts for the relatively large proportion of rotatable moments and for the observed temperature dependence of exchange-bias field.