Large exchange bias induced by polycrystalline Mn₃Ga antiferromagnetic films with controlled layer thickness

Polycrystalline Mn₃Ga layers with thickness in the range from 6-20 nm were deposited at room temperature by a high target utilisation sputtering. To investigate the onset of exchange-bias, a ferromagnetic Co_0.6Fe_0.4 layer (3.3-9 nm thick) capped with 5 nm Ta, were subsequently deposited. X-ray diffraction measurements confirm the presence of Mn₃Ga (0 0 0 2) and (0 0 0 4) peaks characteristic of the D0₁₉ antiferromagnetic structure. The 6 nm thick Mn₃Ga film shows the largest exchange bias of 430 Oe at 120 K with a blocking temperature of 225 K. The blocking temperature is found to decrease with increasing Mn₃Ga thickness. These results in combination with x-ray reflectivity measurements confirm that the quality of the Mn₃Ga/Co_0.6Fe_0.4 interface controls the exchange bias, with the sharp interface with the 6-nm-thick Mn₃Ga inducing the largest exchange bias. The magneto-crystalline anisotropy for 6 nm thick Mn₃Ga thin film sample is calculated to be . Such a binary antiferromagnetic Heusler alloy is compatible with the current memory fabrication process and hence has a great potential for antiferromagnetic spintronics.