Near-Zero Moment Ferromagnetism in the Semiconductor SmN

TL;DR

This study reveals near-zero moment ferromagnetism in SmN with a very small magnetic moment and high coercivity, driven by a delicate balance of spin and orbital contributions in a semiconductor.

Contribution

It provides the first detailed investigation of ferromagnetic order and magnetic properties in SmN, highlighting the near cancellation of spin and orbital moments as a key feature.

Findings

Ferromagnetic order with T_c of 27 K observed in SmN.

Residual magnetization at 2 K is extremely small (0.035 μ_B per Sm).

Large coercive field exceeding 6 T below 15 K.

Abstract

The magnetic behaviour of SmN has been investigated in stoichiometric polycrystalline films. All samples show ferromagnetic order with Curie temperature (T_c) of 27 +/- 3 K, evidenced by the occurrence of hysteresis below T_c. The ferromagnetic state is characterised by a very small moment and a large coercive field, exceeding even the maximum applied field of 6 T below about 15 K. The residual magnetisation at 2 K, measured after cooling in the maximum field, is 0.035 mu_B per Sm. Such a remarkably small moment results from a near cancellation of the spin and orbital contributions for Sm3+ in SmN. Coupling to an applied field is therefore weak, explaining the huge coercive field . The susceptibility in the paramagnetic phase shows temperature-independent Van Vleck and Curie-Weiss contributions. The Van Vleck contribution is in quantitative agreement with the field-induced admixture of the J=7/2 excited state and the 5/2 ground state. The Curie-Weiss contribution returns a Curie temperature that agrees with the onset of ferromagnetic hysteresis, and a conventional paramagnetic moment with an effective moment of 0.4 mu_B per Sm ion, in agreement with expectations for the crystal-field modified effective moment on the Sm3+ ions.