Magnetic and transport properties of amorphous, B2 and L21 Co2MnGa thin films

We have studied the magnetic and transport properties of Co2MnGa (CMG) thin films grown on MgO(100) substrates in terms of their chemical evolution from amorphous to ordered L21 phases at the substrate temperature Ts during the thin film deposition. Interestingly, the chemical order and magnetic properties sharply change depending on Ts. The CMG film deposited at Ts = 550 °C exhibits the L21-ordered structure and the magnetization of 3.5 μB/f.u., while the CMG film deposited at Ts = 300 °C shows a B2-ordered structure and a relatively lower magnetization of 3 μB/f.u., possibly due to the Mn–Mn antiferromagnetic interactions. A metallic behavior of the electrical resistivity appeared in the CMG film deposited at Ts = 550 °C, whereas the semiconducting behavior appeared in the CMG films deposited at 300 °C and room temperature. Moreover, we found that the absolute value of α = d(Δρ)/d(T1/2) in the low-temperature range below about 20 K is a measure to evaluate the degree of the chemical disorder. In a Hall effect measurement, the L21-ordered CMG film obtained at Ts = 550 °C shows a sizable anomalous Hall resistivity of 15 µΩ cm. This study unveils the relation between Ts and atomic ordering, providing a new pathway for optimizing the chemical order.