77Se NMR Investigation of Fe-doped Bi2Se3

TL;DR

This study uses 77Se NMR spectroscopy to investigate the effects of Fe doping in Bi2Se3, revealing how Fe influences relaxation mechanisms and defect distributions relevant to thermoelectric and topological insulator properties.

Contribution

It provides new insights into the spin relaxation processes and defect distributions in Fe-doped Bi2Se3 using 77Se NMR spectroscopy, advancing understanding of magnetic impurity effects.

Findings

Fe dopants induce spin diffusion relaxation at low temperatures.

Above 320 K, relaxation is dominated by interaction with conduction carriers with an activation energy of 21.5 kJ/mol.

Negligible resonance narrowing suggests a statistical defect distribution.

Abstract

Bismuth selenide is both a thermoelectric material and topological insulator. Defects and dopants create conduction in thermoelectric applications. However, such defects may degrade the performance as a topological insulator (TI). Magnetic impurities such as iron open a band gap at the Dirac point on the surface. Since magnetically-doped TIs are important in technological applications, a good understanding of their properties is needed. In this article, 77Se nuclear magnetic resonance (NMR) spectroscopy has been used to investigate Fe-doped Bi2Se3. Spin-lattice relaxation measurements indicate that the Fe dopants provide a spin diffusion relaxation mechanism at low temperatures for the 77Se. Above 320 K, the predominant 77Se relaxation mechanism resulting from interaction with the conduction carriers is thermally induced with an activation energy of 21.5 kJ/mol (5.1 kcal/mol, 222 meV) and likely arises from inter-band excitations. Magic-angle spinning produces negligible narrowing of the 77Se resonance at 7 T, suggesting a statistical distribution of material defects and is also consistent with a dipolar interaction with the neighboring quadrupolar nucleus.