Structural, electronic, and magnetic investigation of magnetic ordering in MBE-grown Cr _x Sb _2−x Te ₃ thin films

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 x = 0.42 (in CrxSb2−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 ∼2 μB to almost 3 μB per Cr ion. The transition temperature (Tc) depends strongly on the Cr concentration and is found to increase with doping concentration. For the highest achievable doping level for phasepure films of x = 0.42, a Tc 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.

Magnetic proximity coupling to Cr-doped Sb2Te3 thin films

“…The thin film deposition took place at a substrate temperature of 250 • C. A detailed description of the growth procedure can be found in Ref. [14].…”

“…Structural and magnetic characterization was carried out using XRD and SQUID magnetometry (for details see Ref. [14]). Out-of-plane XRD measurements show that the films are free from secondary phases, such as chromium tellurides, which have T C s between 180 and 340 K [24].…”

“…Despite this more than doubled T C it is still well below accessible temperatures for practical applications. On the other hand, magnetic ordering at much higher temperatures has been reported for Cr x Sb 2−x Te 3 thin films, such as 125 K for x = 0.42 [14] and 190 K for x = 0.59, following a nearly linear increase with Cr doping [17].…”

“…V-and Cr-doping of (Sb,Bi) 2 (Se,Te) 3 have proven to be some of the most promising ways of producing MTIs [12][13][14], allowing for the experimental verification of the QAHE [15]. For Cr-doped Bi 2 Se 3 , it has previously been demonstrated that the ferromagnetic transition temperature, T C , can be enhanced from 7-19 K through the deposition of a Co layer onto the surface of the MTI [16].…”

“…Recently, we reported the structural, electronic, and magnetic investigation of molecular beam epitaxy (MBE)-grown Cr x Sb 2−x Te 3 thin films (x = 0.15, 0.26, 0.42) using x-ray diffraction (XRD), atomic force microscopy, superconducting quantum interference device (SQUID) magnetometry, magnetotransport, and polarized neutron reflectometry, showing these materials retain good crystalline order [14]. X-ray magnetic circular dichroism (XMCD) measurements on Crdoped (Sb,Bi) 2 Te 3 were recently reported by Ye et al [18].…”