Extreme field-sensitivity of the magnetic tunneling in Fe-doped Li$_3$N

TL;DR

This study reveals that Fe-doped Li$_3$N exhibits highly sensitive quantum tunneling of magnetization, with sharp resonances affected by small magnetic fields, making it an ideal model for understanding quantum magnetic phenomena at low temperatures.

Contribution

It demonstrates the extreme field sensitivity of magnetic tunneling in Fe-doped Li$_3$N and highlights its potential as a simple model system for quantum magnetization tunneling studies.

Findings

Spin-relaxation becomes temperature-independent below 10 K.

Transverse magnetic fields significantly increase spin-flip probability.

Longitudinal fields suppress tunneling by lifting ground-state degeneracy.

Abstract

The magnetic properties of dilute Li$_2$(Li$_{1-x}$Fe$_x$)N with $x \sim 0.001$ are dominated by the spin of single, isolated Fe atoms. Below $T = 10$ K the spin-relaxation times become temperature-independent indicating a crossover from thermal excitations to the quantum tunneling regime. We report on a strong increase of the spin-flip probability in $\textit{transverse}$ magnetic fields that proves the resonant character of this tunneling process. $\textit{Longitudinal}$ fields, on the other hand, lift the ground-state degeneracy and destroy the tunneling condition. An increase of the relaxation time by four orders of magnitude in applied fields of only a few milliTesla reveals exceptionally sharp tunneling resonances. Li$_2$(Li$_{1-x}$Fe$_x$)N represents a comparatively simple and clean model system that opens the possibility to study quantum tunneling of the magnetization at liquid helium temperatures.