Ferromagnetic–antiferromagnetic Fe/NiO (1 0 0) interface studied by non-linear Kerr effect S. Colonna a, * , F. Ronci a , A. Cricenti a,c , P. Luches b , S. Valeri b , J. Qi c , Y. Xu c , J.K. Miller c , N. Tolk c a CNR–Istituto di Struttura della Materia, Via del Fosso del Cavaliere 100, I-00133 Roma, Italy b S3-INFM Dipartimento di Fisica, Universita ` di Modena e Reggio Emilia, via G. Campi 213/a, I-41100 Modena, Italy c Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA Available online 13 June 2007 Abstract In this work, the magnetic properties of the Fe/NiO (1 0 0) interface at room temperature is investigated using non-linear magneto- optical Kerr effect. Nickel oxide is a promising material for technological applications due to its Ne ´el temperature (525 K) occurring well above the room temperature. Non-linear Kerr rotation measurements have demonstrated to be an effective way to investigate a ferro- magnetic/antiferromagnetic interface. The measurements here reported demonstrate that the magnetic properties of the studied interface strongly depend on the Fe layer thickness. In fact, a clear hysteresis loop is observed only for a thickness higher than 5 ML, whereas for the 2 ML sample the hysteresis loop completely disappears. These results are in agreement with previous structural characterizations of the interface. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Exchange bias; Non-linear optics; Kerr effect 1. Introduction The interface formed between a ferromagnetic (FM) and an antiferromagnetic (AFM) material has been a subject of study since the discovery of the exchange bias phenome- non, which is characterized by a shift of the hysteresis loop of the ferromagnetic layer in the direction of the applied field [1]. This subject has recently received strong renewed interest due to the application of the exchange bias in recording media and reading heads in data storage devices. Different models for the description of the exchange bias mechanism have been proposed, however, a general quan- titative description is still lacking. Nickel oxide is a promising material for technological applications due to its Ne ´el temperature (525 K) which is well above room temperature. The Fe grows on the NiO (1 0 0) surface on top oxygen atoms thus the surface crystal cell is rotated 45° with respect to the underling [1 0 0] direc- tion of the substrate [2,3]. A comprehensive understanding of the chemical and physical properties of the interface is of paramount importance for future applications. Several studies have demonstrated that the Fe/NiO interface is not entirely abrupt but an oxygen diffusion takes place resulting in a reduced NiO layer [2–5]. A structural charac- terization of the Fe/NiO interface previously conducted by X-ray absorption spectroscopy in combination with den- sity functional calculations has provided evidence that a FeO-like layer is formed at the interface between the metal and the oxide [6]. As a consequence the magnetic moment of the Fe atoms at the interface are increased. Uncompen- sated moments coming from the interfacial FeO layer, which may couple ferromagnetically with the Fe layer, are expected to dramatically influence the exchange inter- action at the Fe/NiO interface, with deep consequences also for the exchange bias mechanism. 0039-6028/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2007.06.011 * Corresponding author. Tel.: +39 06 4993 4163; fax: +39 06 4993 4153. E-mail address: colonna@ism.cnr.it (S. Colonna). www.elsevier.com/locate/susc Surface Science 601 (2007) 4362–4365