Eur. Phys. J. B 77, 337-343 (2010)
https://doi.org/10.1140/epjb/e2010-00271-6

Spin-fluctuation mediated high-temperature ferromagnetism in Si:Mn dilute magnetic semiconductors

¹ RRC Kurchatov Institute, Kurchatov Sqr. 1, 123182 Moscow, Russia
² SMC-INFM-CNR and Dipartimento di Fisica, Università di Roma “La Sapienza”, piazzale Aldo Moro 2, 00185 Roma, Italy

Corresponding author: ^a sergio.caprara@romal.infn.it

Received: 10 June 2010
Published online: 22 September 2010

Abstract

We discuss a possible route to explain high-temperature ferromagnetism in Si:Mn dilute magnetic semiconductors. We argue that most Mn atoms are segregated within nanometer-sized regions of magnetic precipitate and form the alloy, or compound, MnSi_2-z with z ≈ (0.250.30), whereas a small minority of Mn atoms forms Ångström-sized magnetic defects embedded in the host. Assuming that MnSi_2-z is a weak itinerant ferromagnet which supports sizable spin fluctuations (paramagnons) far above the intrinsic Curie temperature, we show that the Stoner enhancement of the exchange interaction between the local magnetic moments of the defects occurs. As a result, a significant increase of the temperature of global ferromagnetic order in the system is achieved. We develop a phenomenological approach, to qualitatively describe this effect.