Recently, it has been observed that thin ferromagnetic Fe films deposited on top of (Ga,Mn)As layers induce a significant proximity polarization in the (Ga,Mn)As film even at room temperature. Furthermore, it was found that a thin interfacial region of the (Ga,Mn)As film is coupled antiferromagnetically to the Fe layer. Here we report a series of combined x-ray magnetic dichroism and superconducting quantum interference device magnetometer measurements for Fe/(Ga,Mn)As bilayers where the (Ga,Mn)As layer thickness is varied between 5 and 50 nm. We find a reorientation transition of the magnetic proximity polarization as a function of the (Ga,Mn)As thickness. The data are compared to results obtained performing ab initio calculations. A varying concentration of Mn interstitials as a function of (Ga,Mn)As layer thickness is responsible for this reorientation. Furthermore, exchange bias is studied in the fully epitaxial bilayer system. We find a rather strong ferromagnetic exchange bias. The strength of the exchange bias can be estimated by using a simple partial domain wall model. The diluted magnetic semiconductor (DMS) GaMnAs is a promising material for semiconducting spintronic devices. However, the record values of the Curie temperature seem to stagnate below 200 K 6 with no clear strategy to further increase it above room temperature.A novel route toward increasing the ordering temperature is to engineer the material using ferromagnetic metal overlayers. Tuning the magnetic properties at FM metal/DMS-based interfaces based on the most representative DMS system (Ga,Mn)As 7 has recently been explored in a variety of experiments. For example, exchange bias is observed in MnAs/(Ga,Mn)As bilayers. [8][9][10] In contrast, NiFe/(Ga,Mn)As bilayers show an independent magnetization behavior 11 with no exchange bias. In the Fe/(Ga,Mn)As system, the Fe overlayer induces a proximity polarization antiparallel to the Fe moment within a 1-2 nm (Ga,Mn)As region, which is promising for improving the ferromagnetic properties of very thin (Ga,Mn)As films. [12][13][14] In fact, we have recently demonstrated that the proximity effect effectively enhances the operation temperature of Fe/(Ga,Mn)As hybrid spin injection devices when very thin (Ga,Mn)As injector and detector contacts are capped by an iron layer. 15 However, to take full advantage of the control of the magnetization of the (Ga,Mn)As injector/detector contacts, it is of importance to understand the coupling mechanism in this epitaxial FM metal/DMS bilayer system. Here we map out the influence of the (Ga,Mn)As thickness in fully epitaxial Fe/(Ga,Mn)As heterostructures on the interfacial coupling as well as on the magnetization properties of the bulk layer by a combined study using element-specific x-ray magnetic circular dichroism (XMCD) measurements and bulk-sensitive superconducting quantum interference device (SQUID) magnetometry. By means of XMCD we are able to identify a thickness dependent reorientation transition of the Mn magnetization from antiparallel to paral...