Structural, electronic, and magnetic investigation of magnetic ordering in MBE-grown Cr_xSb_2−xTe₃ thin films

¹ Department of Physics, Clarendon Laboratory, University of Oxford - Oxford, OX1 3PU, UK
² ISIS, STFC, Rutherford Appleton Lab - Didcot, OX11 0QX, UK
³ Cavendish Laboratory, University of Cambridge - Cambridge CB3 0HE, UK
⁴ IBM Almaden Research Center - 650 Harry Road, San Jose, CA 95120, USA
⁵ Toshiba Research Europe Ltd, Cambridge Research Laboratory - Cambridge CB4 0GZ, UK
⁶ Magnetic Spectroscopy Group, Diamond Light Source - Didcot, OX11 0DE, UK

^(a) Thorsten.Hesjedal@physics.ox.ac.uk (corresponding author)

Received: 4 July 2016
Accepted: 1 August 2016

Abstract

We report the structural, electronic, and magnetic study of Cr-doped Sb₂Te₃ thin films grown by a two-step deposition process using molecular-beam epitaxy (MBE). The samples were investigated using a variety of complementary techniques, namely, x-ray diffraction (XRD), atomic force microscopy, SQUID magnetometry, magneto-transport, and polarized neutron reflectometry (PNR). It is found that the samples retain good crystalline order up to a doping level of (in Cr_xSb_2−xTe₃), above which degradation of the crystal structure is observed by XRD. Fits to the recorded XRD spectra indicate a general reduction in the c-axis lattice parameter as a function of doping, consistent with substitutional doping with an ion of smaller ionic radius. The samples show soft ferromagnetic behavior with the easy axis of magnetization being out-of-plane. The saturation magnetization is dependent on the doping level, and reaches from to almost per Cr ion. The transition temperature depends strongly on the Cr concentration and is found to increase with doping concentration. For the highest achievable doping level for phase-pure films of , a of 125 K was determined. Electric transport measurements find surface-dominated transport below ∼10 K. The magnetic properties extracted from anomalous Hall effect data are in excellent agreement with the magnetometry data. PNR studies indicate a uniform magnetization profile throughout the film, with no indication of enhanced magnetic order towards the sample surface.