Fe/Cr/Fe(001) trilayers have been studied by means of spin polarized inverse photoemission and absorbed current spectroscopies. A reversal of the magnetic ordering of the Fe overlayer with respect to the buried Fe substrate as a function of the Cr spacer thickness is observed, confirming the oscillating transition from ferromagnetic (FM) to antiferromagnetic (AF) coupling between the Fe layers. The possible surfactant action of oxygen in the trilayer growth has also been investigated using a Fe(001)-p(1x1)O surface as a substrate, with the aim of obtaining more ordered interfaces. It is found that the FM-AF oscillations in Fe/Cr/Fe(001)-p(1x1)O occurs with the same periodicity as in Fe/Cr/Fe trilayers grown at room temperature, namely 12 monolayers (ML), while a short 2 ML period, observed in high temperature grown samples, is absent.