Exchange bias and coercivity of _{Ni80 Fe20 layer coupled with Fe-doped Cr2} O₃

We have investigated the exchange bias and the coercivity in the ferromagnet Ni80 Fe20 (NiFe) layer coupled with a polycrystalline Cr2 (1-x) Fe2x O₃ (CFO; x=0.1,0.25) layer, which is known as an antiferromagnet with spiral spin order. For x=0.1, the exchange bias HEX and the coercivity HC at 10 K were 152 and 230 Oe, respectively, but their magnitudes rapidly decreased from 10 to 50 K at the temperature range that showed a splitting between zero-field-cooling and field-cooling magnetization data for the CFO target. This implies that the CFO has an unknown magnetic transition around ∼50K in addition to the spiral antiferromagnetic transition at ∼250 K. For x=0.25, on the other hand, the exchange bias rapidly decreased from ∼170 Oe at 10 K to zero at ∼90 K.