Alternating magnetic anisotropy of Li$_2$(Li$_{1-x}T_x$)N with $T$ = Mn, Fe, Co, and Ni

TL;DR

This study investigates how substituting transition metals Mn, Fe, Co, and Ni into Li$_2$(Li$_{1-x}T_x$)N affects magnetic anisotropy, revealing alternating easy-plane and easy-axis behaviors due to unquenched orbital moments.

Contribution

It introduces a detailed analysis of magnetic anisotropy in Li$_2$(Li$_{1-x}T_x$)N with transition metal substitution, supported by a single-ion model that explains the alternating anisotropy behavior.

Findings

Large magnetic anisotropies due to unquenched orbital moments.

Alternating easy-plane and easy-axis anisotropy with different transition metals.

Good agreement between experimental results and the single-ion model.

Abstract

Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be substituted for Li in single crystalline Li$_2$(Li$_{1-x}T_x$)N. Isothermal and temperature-dependent magnetization measurements reveal local magnetic moments with magnitudes significantly exceeding the spin-only value. The additional contributions stem from unquenched orbital moments that lead to rare-earth-like behavior of the magnetic properties. Accordingly, extremely large magnetic anisotropies have been found. Most notably, the magnetic anisotropy alternates as easy-plane $\rightarrow$ easy-axis $\rightarrow$ easy-plane $\rightarrow$ easy-axis when progressing from $T$ = Mn $\rightarrow$ Fe $\rightarrow$ Co $\rightarrow$ Ni. This behavior can be understood based on a perturbation approach in an analytical, single-ion model. The calculated magnetic anisotropies show a surprisingly good agreement with the experiment and capture the basic features observed for the different transition metals.