Suppression of interfacial intermixing between MBE-grown Heusler alloy Ni_2MnIn and (001 )InAs or InAs-HEMT structures

摘要

This paper reports on the application of a thin MgO interlayer as a diffusion barrier between a Ni_2MnIn Heusler film and the substrate consisting of either (0 0 l)InAs or a high electron mobility transistor structure with an InAs channel layer. The functionality of the MgO interlayers is studied in dependence of their layer thicknesses. Our studies reveal that MgO interlayers are effective diffusion barriers, which in conjunction with post-growth annealing significantly improve the structural and magnetic properties of the Heusler films. For all as-grown samples, a Curie temperature of 170 K was found indicating that the Ni_2MnIn films are crystallized in the B2 phase. Post-growth annealing for 15 h at 350 °C of samples with MgO layer thicknesses smaller than 3 nm leads to a strong decrease in magnetisation. This film degradation may be attributed to the intermixing of the Heusler films with substrate material through not-completely closed MgO films. For samples with a MgO interlayer thickness of 3 nm, the Curie temperature increases up to 300 K. This Curie temperature is close to the value reported for bulk Ni_2MnIn films in the desired L2_1 phase. Furthermore, an increase in saturation magnetisation by a factor of 2.4 was observed.