Magnetic second harmonic study of Cr/Fe and Ag/Fe buried interfaces F. Bisio * , L. Balbi, G. Gonella, R. Moroni, M. Canepa, L. Mattera Unit  a INFM and CFSBT, Dipartimento di Fisica, Universit  a di Genova, via Dodecaneso 33, I-16146 Genova, Italy Abstract The magnetic properties of Ag/Fe/MgO and Cr/Fe/MgO multilayers have been studied in air by both linear (MOKE) and non-linear (MSHG) magneto-optics. Thanks to the different probing sensitivities of the two techniques, film and interface properties can be separately measured. In the Ag/Fe/MgO case, coercive field values measured with linear and non-linear optics are very similar, indicating that a sharp interface is formed and that the presence of silver on top of iron does not alter its magnetic properties. The values of coercive field measured with MOKE for the Cr/Fe/ MgO multilayer differ significantly with respect to the Ag case, and furthermore different coercive fields have been measuredonthissystemwithMOKEandMSHG.Weascribetheobservedeffectstospinfrustrationcausedthelayered antiferromagnetic Cr spin structure along with the presence of steps at the Cr/Fe interface. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Second harmonic generation; Iron; Magnetic interfaces 1. Introduction The investigation of magnetic properties of low dimensional systems, such as magnetic surfaces, films and multilayers, has increased in importance over the past decades; the interest in studying such systems is mainly due to the fact that, in most of thecases,duetotheirreduceddimensionality,their physical properties are significantly different with respect to the ones of their bulk counterparts [1]; this fact makes them both very attractive for fun- damental research and appealing for a great vari- ety of innovative technological applications. The recent discovery of phenomena such as the giant magnetoresistance [2] and the oscillatory coupling between magnetic layers separated by non-magnetic spacers [3,4] has promoted further research in this field. The magnetic properties ex- hibited by these systems have been found to be strongly dependent on the structure of the inter- faces between adjacent layers, thus making the study of interfaces a subject of crucial importance [5]. The experimental investigation of buried in- terface properties is however made difficult by the fact that most conventional surface science experi- mental techniques cannot probe interfaces buried more than a few atomic spacings below the sur- face. Second harmonic generation (SHG) [6], however, combines surface and interface sensitiv- ity for centrosymmetric media and relatively large radiation penetration depth: the combination of the two effects leads to the possibility of selectively probing properties of buried interfaces, as long as they are accessible to radiation. SHG has been Surface Science 507–510 (2002) 530–534 www.elsevier.com/locate/susc * Corresponding author. Fax: +39-010-311066. E-mail address: bisio@fisica.unige.it (F. Bisio). 0039-6028/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0039-6028(02)01304-3