Magnetic Properties of Microfabricated MnxGa Circler Dot Arrays

Mn-Ga alloy attracts much attention as a new material for the spintronics device and the high-density magnetic storage media because of its high uniaxial crystalline magnet anisotropy (~10⁷erg/cm³) [1]. A lot of studies of Mn-Ga thin films have been performed [2], however, there are few reports about the Mn-Ga thin film in submicron size. In this study, Mn_xGa circular dot arrays have been microfabricated and a relation between the magnetic properties and the diameter of the dots have been investigated in order to obtain the design guide line of new high-performance magnetic thin film material for high-density magnetic recording. The Mn_xGa thin films ware prepared by an electron beam deposition system with Mn_xGa bulk deposition materials synthesized by the arc melting. A Cr buffer layer (5 nm) and a Mn_xGa layer (10 ~ 20 nm) were stacked on a single crystal MgO (100) substrate, finally, a Cr capping layer was deposited. The Mn_xGa circular dots were microfabricated from the continuous films through an electron beam lithography and an Ar ion milling. Diameter of the dots D was varied from 100 nm to 3000 nm. The composition of the deposition materials and the thin films was identified by an energy dispersive X-ray spectrometer (EDX). Surface of the substrate, the buffer, and the Mn_xGa layers was monitored by a reflection high energy electron diffraction (RHEED) in situ observation. Crystalline structure of the films was characterized by an X-ray diffraction (XRD). Magnetic properties of the films and the dots were characterized by a super conducting quantum interference devise magnetometer (SQUID) and a poler magneto optical Kerr effect ( μ -MOKE) with the maximum magnetic field of ±70 kOe and ±20 kOe, respectively. From XRD pattern for the Mn_1.0Ga thin film deposited at 300 °C and annealed at 500 °C, (001) superlattice peak and (002) fundamental peak were observed, indicating that the L1₀ ordered structure was formed. For the Mn_1.5Ga and the Mn3.2 Ga, the peaks from the L1₀ or D0₂₂ structure were not confirmed. M_s=170 emu/ cm³ and H_c=10.5 kOe was observed from magnetization curve for the Mn_1.0Ga thin film with out-of-plane applied field. After the microfabrication of Mn_1.0Ga continuous film, H_c = 14.6 kOe was observed in the dots with D = 3000 nm. H_c of the dots showed increase tendency with decrease of D. The relation between magnetic properties and the diameter of the Mn_xGa dots will be discussed in detail.