Physica B 384 (2006) 184–186 Monte Carlo simulations of a ferromagnetic-FeF 2 system Orlando V. Billoni Ã,1 , Francisco A. Tamarit 1 , Sergio A. Cannas 1 Facultad de Matema´tica, Astronomı´a y Fı´sica, Universidad Nacional de Co´rdoba, Ciudad Universitaria, 5000 Co´rdoba, Argentina Abstract In this work, we perform Monte Carlo simulations to study the magnetization reversal mechanism in ferromagnetic thin films on FeF 2 . In particular, we emulate a bilayer AFM/FM structure, where the AFM interface corresponds to an uncompensated (1 0 0) plane. The magnetic moments are modeled by classical Heisenberg spin variables. Our analysis focus on the role of the exchange interaction J AF between the FM spins and the spins belonging to the AFM interface on the reversal mechanisms of the magnetization. By simulating hysteresis loops we study the effect of temperature on the bias field. r 2006 Elsevier B.V. All rights reserved. PACS: 75.70.i; 75.60.Jk Keywords: Exchange bias; Monte Carlo simulation; Thin films 1. Introduction Exchange bias (EB) is an effect arising typically at an interface between a ferromagnetic (FM) and an antiferro- magnetic (AFM) material when the Curie temperature of the former is larger than the Ne`el temperature of the latter. If the system is cooled under an applied field H cf below the ordering temperature of the antiferromagnet, the center of the hysteresis loop usually shifts opposite to the cooling field by an amount H EB , called the exchange bias field. Although this phenomenon was observed long time ago [1] there are still many controversies concerning the under- lying mechanisms responsible for this effect [2–4]. Beyond the theoretical interest, this phenomenon is also relevant in practical applications like for instance magnetic sensors and magnetic recording media [3]. The characterization of the spin structure in the nearest planes to the interface is a main topic in the understanding of the EB phenomena. In particular, interfaces can be roughly classified as compen- sated and uncompensated, depending on whether they have zero or nonzero net magnetization, respectively. Most of the earliest models that explain EB assume an uncompen- sated interfacial spin structure even when this requirement is not always fulfilled in experiments. In fact, experiments carried out by Moran et al. [5] and Nogue´s et al. [6] on Fe films grew over FeF 2 single crystals cut along different orientation showed that H EB is larger when the interface is compensated ((1 1 0) plane) in comparison with the uncompensated interface in the (1 0 0) plane. This effect was supposed to be associated with spin rearrangement at the interface [3,6]. In this work, we analyze the hysteresis loop of a bilayer FM–FeF 2 with an uncompensated interface corresponding to the (1 0 0) plane using Metropolis Monte Carlo simulations to analyze the existence of spin rearrangement. We are mainly concerned with the influence of the strength of the interaction between the FM and AFM layers. 2. Model We studied one FM film mounted over other AFM film. The films are magnetically coupled each other by exchange interactions and the structure of both films is a body- centered cubic lattice with a perfect match across the FM/ AFM interface. To perform the numerical simulations we ARTICLE IN PRESS www.elsevier.com/locate/physb 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.222 Ã Corresponding author. Tel.: +54 351 4334051; fax: +54 351 4334054. E-mail address: billoni@famaf.unc.edu.ar (O.V. Billoni). 1 Member of CONICET (Argentina)