Re-entrant ferromagnetism in a generic class of diluted magnetic semiconductors

TL;DR

This paper theoretically predicts a re-entrant ferromagnetic behavior in doped semiconductors, where two distinct ferromagnetic phases are separated by a paramagnetic phase due to competing exchange mechanisms.

Contribution

It introduces a generic theoretical model showing the possibility of three ferromagnetic transition temperatures and re-entrant ferromagnetism in diluted magnetic semiconductors.

Findings

Three ferromagnetic transition temperatures (T_1 > T_2 > T_3) predicted.

Re-entrant ferromagnetism with a paramagnetic phase between two ferromagnetic phases.

Potential observation in diluted magnetic semiconductors and magnetic oxides.

Abstract

Considering a general situation where a semiconductor is doped by magnetic impurities leading to a carrier-induced ferromagnetic exchange coupling between the impurity moments, we show theoretically the possible generic existence of three ferromagnetic transition temperatures, T_1 > T_2 > T_3, with two distinct ferromagnetic regimes existing for T_1 > T > T_2 and T < T_3. Such an intriguing re-entrant ferromagnetism, with a paramagnetic phase (T_2 > T > T_3) between two ferromagnetic phases, arises from a subtle competition between indirect exchange induced by thermally activated carriers in an otherwise empty conduction band versus the exchange coupling existing in the impurity band due to the bound carriers themselves. We comment on the possibility of observing such a re-entrance phenomenon in diluted magnetic semiconductors and magnetic oxides.