Magnetic and magnetotransport properties of Bi$_2$Se$_3$ thin films doped by Eu

TL;DR

This study investigates how Eu doping affects the structural, magnetic, and magnetotransport properties of Bi2Se3 thin films, revealing non-uniform Eu distribution, persistent weak antilocalization, and a transition to ferromagnetism with increasing Eu content.

Contribution

It provides new insights into Eu distribution, magnetic phase transition, and magnetotransport behavior in Eu-doped Bi2Se3 thin films synthesized by MBE.

Findings

Eu forms pancake-like clusters within the films.

Weak antilocalization persists up to 15K despite Eu doping.

Ferromagnetic transition occurs around Eu content x=0.1, with Curie temperature increasing to 64K at x=0.21.

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 $\approx$ 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.