Magnetic and magnetotransport properties of Bi2Se3 thin films doped by Eu

Abstract

Structural, magnetic and magnetotransport properties of (Bi 1−x Eu x ) 2 Se 3 thin films have been studied experimentally as a function of Eu content. The films were synthesized by MBE. It is demonstrated that Eu distribution is not uniform, it enter quint-layers forming inside them plain (pancake-like) areas containing Eu atoms, which sizes and concentration increase with the growth of Eu content. Positive magnetoresistance related to the weak antilocalization was observed up to 15K. The antilocalization was not followed by weak localization as theory predicts for nontrivial topological states. Surprisingly, the features of antilocalization were seen even at Eu content x = 0.21. With the increase of Eu content the transition to ferromagnetic state occurs at x about 0.1 and with the Curie temperature ≈ 8K, that rises up to 64K for x = 0.21. At temperatures above 1-2 K, the dephasing length is proportional to T −1/2 indicating the dominant contribution of inelastic e-e scattering into electron phase breaking. However, at low temperatures the dephasing length saturates, that could be due to the scattering on magnetic ions.

Effect of Sr doping on structure, morphology, and transport properties of Bi2Se3 epitaxial thin films

“…It is not necessarily that Sr atoms are randomly distributed in the lattice. We can't exclude formation of metal-rich nanoclusters [29,41], flat inclusions [42], segregation [43], or even well arranged blocks [44]. However, in XRD similar imperfections are usually manifested just as a broadening of the reflections, while detection of the specific Sr-enriched structures by means of TEM is rather challenging.…”

“…Thin films with different Sr content were obtained by varying the evaporation temperature of the Sr effusion cell. Sr concentration x in the grown films was increased from 0.003 to 0.352 when heating Sr cell from 260 to 380 • C. When growing Bi 2 Se 3 films from elemental Bi and Se sources [18][19][20][21]23] it is inevitable to employ a two-step deposition method due to a weak interaction of Bi and Se ad-atoms with the substrate, with the first step temperature being below 150 • C. Beam flux composition, generated from effusion cell loaded with binary Bi 2 Se 3 compound [22,28,29], consists of Bi-Se molecular species [24], and thin film condensation occurs at the elevated temperatures. So, time consuming low temperature stage becomes unnecessary.…”

Magnetic Topological Insulator Heterostructures: A Review

“…However, despite having achieved substitutional doping of high-quality Bi 2 Te 3 films with Gd, Dy, and Ho, [80][81][82] all films remained essentially paramagnetic with some hints of antiferromagnetic behavior. [80][81][82][83][84] Although Eu-doped Bi 2 Se 3 has demonstrated ferromagnetism with over 10% Eu concentration, the doing profile in this system is not uniform, [85] which is an issue for transport measurements. Nevertheless, for Dy doping, it is already shown that low fields of 0.65 T can result in induced moments on the order of ≈1/3 of the full Dy 3 + moment in Dy:Bi 2 Te 3 .…”

Magnetism of Bi2Se3 thin films with Eu-rich flat inclusions

“…The Eu-doped Bi 2 Se 3 thin films were synthesized by the molecular-beam epitaxy technique using evaporation cells with binary Bi 2 Se 3 source as well as cells with elemental Bi, Se, and Eu. More detailed description of the growth process and structural characterization of studied films can be found in [16,17]. For simplicity, we can consider our films as ternary (Bi 1−x Eu x ) 2 Se 3 compounds and use x as a measure of Eu content.…”