Studies on Fe-based Heterostructures and Thin Films

Abstract

We have investigated magnetic and electronic properties of various Fe-based magnetic thin films and heterostructure systems using soft x-ray spectroscopy. Excellent quality epitaxial samples were fabricated by an electron beam evaporation, a thermal evaporation and a pulsed laser deposition (PLD) techniques. The interfacial electronic structure of heterostructure and magnetic anisotropy of ultrathin film were explored by soft x-ray absorption spectroscopy (XAS), magnetic circular dichroism (XMCD), and spin resolved photoemission spectroscopy (SRPES). The epitaxial strain dependent spin reorientation transition phenomena of a canted antiferromagnetic material was studied using magnetic linear dichroism (XMLD) and SQUID measurements. The existence of oxide layers for interface between MgO and Fe was explored. MgO/Fe bilayer system is a preliminary system of Fe/MgO/Fe magnetic tunnel junctions. We found that no iron oxide layer at the interface for the in-situ grown epitaxial MgO(001)/Fe(001) bilayer on W (001) substrate with photoemission spectroscopy and XAS. Moreover, it is shown that metal Mg can revivify the iron oxide to metal Fe with forming MgO. From these results, we prove that we can make iron oxide-free samples in the Mg rich growth condition. Furthermore, the electronic structures of interface Fe with and without MgO were investigated using SRPES measurement and LDA calculation. They show that the interface dz2 electrons aremost affected by MgO overlayer, and these electronic structure change of interface Δ1 electrons largely influences on the symmetry filter tunneling process.In-plane magnetic anisotropy in ultrathin Fe films has been studies by XMCD technique. Direct measurement of magnetic moment at each direction shows that Fe film thinner than 8 Å on Ag has in-plane magnetic anisotropy. New spin reorientation transition phenomenon is discovered in 8 Å thickness Fe film from perpendicular to in-plane magnetic anisotropy. That is, there are two different spin reorientation transitions with respect to the film thickness in epitaxial Fe film on Ag (001) substrate.Single phase DyFeO3 (110) epitaxial films on SrTiO3 (001) substrates was grown in a layer-by-layer manner using the PLD technique. The Fe L2,3-edge XMLD and magnetic hysteresis confirm that the film shows the spin-canted antiferromagnetism at room temperature and undergoes the spin reorientation transition upon cooling as the bulk. The spin reorientation transition temperature is significantly reduced in the thin films due to the compressive strain, and becomes below 5 K for the thickness < 50 Å.