Perpendicular Magnetic Anisotropy and Spin Glass-like Behavior in Molecular Beam Epitaxy Grown Chromium Telluride Thin Films

Abstract

Reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), vibrating sample magnetometry, and other physical property measurements are used to investigate the structure, morphology, magnetic, and magnetotransport properties of (001)-oriented Cr2Te3 thin films grown on Al2O3(0001) and Si(111)-(7×7) surfaces by molecular beam epitaxy. Streaky RHEED patterns indicate flat smooth film growth on both substrates. STM studies show the hexagonal arrangements of surface atoms. Determination of the lattice parameter from the atomically resolved STM image is consistent with the bulk crystal structures. Magnetic measurements show the film is ferromagnetic, having a Curie temperature of about 180 K, and a spin glass-like behavior was observed below 35 K. Magnetotransport measurements show the metallic nature of the film with a perpendicular magnetic anisotropy along the c-axis.

Angular dependence of magnetization reversal in epitaxial chromium telluride thin films with perpendicular magnetic anisotropy

“…Magnetic and transport measurements were carried out with 9 T Quantum Design physical property measurement system (PPMS) combined with vibrating sample magnetometry (VSM) capable of cooling samples down to ~ 2 K. Sharp streaky features in RHEED patterns from the surface following growth of 4 nm Cr2Te3 thin film indicate high crystalline quality with atomically flat surface morphology. RHEED pattern also indicates the hexagonal structure of the layer grown along (001) direction (c-axis), which is also evident from the X-ray diffraction (XRD) pattern [8]. The growth structurally agrees very well with other reports of the growth of a thin film following hexagonal structure due to substrate crystal symmetry of a hcp(0001) and fcc(111) [19].…”

“…The remanence state is always uniformly magnetized along ±z direction for θ ≤ 80°, whereas, multiple domain walls are observed in the in-plane (θ = 90°) remanence state as shown in Figure 5(c) and 5(d). This also explains the higher magnetoresistance observed in the experiment at zero field for θ = 90° as compared to θ ≤ 80° [8].…”

“…Cr2Te3 films were grown in a custom-built MBE growth system (Omicron, Germany) under ultra-high vacuum (UHV) conditions (base pressure ~1×10 -10 mbar). Details of the system and the growth method have been described elsewhere [8,19]. A reflection high energy electron diffraction (RHEED) setup is attached to the MBE system for in situ monitoring of surface reconstruction and growth.…”

“…[8]). The magnetoresistance shows hysteresis with two sharp maxima at the same magnitude of positive and negative field values that correspond to the switching fields (Hs) [8]. As observed, the saturation field at θ = 90° is ~3.7 T, which is very close to the hard axis saturation field of 3.8 T for the 20 nm thick film (Figure 3).…”

Versatile Large-Area Custom-Feature van der Waals Epitaxy of Topological Insulators

“…The large equilateral trigonal domains observed in the AFM images reflect the trigonal-hexagonal in-plane symmetry of the tetradymite crystal, previously observed in growths involving thin films and/or substrates with hexagonal symmetry. 31,[51][52][53] Figure 2c illustrates a typical layered trigonal domain. The step height between each subsequent layer is approximately 1 nm, which is the thickness of one quintuple layer of the tetradymite crystal structure (see Supporting Figure S2); thus establishing that the BTS domains grow layer-by-layer in an epitaxial fashion.…”