Structural Origins of the Training Effect In NiFe/IrMn/CoFe Exchange Bias Trilayers

Structural Origins of the Training Effect In NiFe/IrMn/CoFe Exchange Bias TrilayersR. Mustafa Oksuzoglu*, S. Pekdemir, M. Emre Sancı, M. Yıldırım, O. DenizDepartment of Materials Science and Engineering, Anadolu University, 26480, Eskisehir, Turkeyrmoksuzoglu@anadolu.edu.trThe exchange bias (EB) effect originated from the magnetic interfacial interaction betweenan antiferromagnetic (AF) and a ferromagnetic (F) layer is indispensable in magnetic data storagesystems. Therefore, EB phenomenology is still investigated in many aspects since its discovery [1].The underlying mechanism and the role of the interface/bulk structure have been investigated in avariety of EB systems [2-4] with different deposition techniques and F/AF materials. An importantphenomenon for storage application in EB systems is the training effect; a gradual degradation ofthe EB field can take place when cycling the heterostructure through consecutive hysteresis loops[5]. This aging phenomenon is known as training effect and is affected by several factors astemperature, AF thickness, anisotropy field, interface roughness, cooling field, dilution, andstructure of AF/F materials [6-8]. Not only understanding of the underlying mechanism of the EBeffect, but also the quenching of the training effect is crucial for application.In the present study, we worked on NiFe/IrMn/CoFe based EB trilayer systems with Ta/Rubuffer/seed layers, which were deposited by pulsed DC unbalanced magnetron sputtering technique,in order to investigate the effects of the interfacial roughness variations and grain size of the IrMnlayer on the EB properties and training effect. The interface roughness is systematically variedwithout any change in the thickness and grain size of IrMn layer enabling investigation of theinfluence of the roughness on both EB and training effects. Additionally, the grains size of the IrMnlayer is systematically varied without any change in the thickness of the IrMn layer, in order tostudy the relationship between grain size and EB and training effects. Structural origins of thetraining effects besides of the origin of the EB in NiFe/IrMn/CoFe based EB trilayer systems werediscussed[1] W.H. Meiklejohn, C.P. Bean, Phys. Rev. 102 (1956) 1413.[2] R. M. Öksüzoğlu, M. Yıldırım, H. Çınar, E. Hildebrandt, L. Alff, J. Magn. Magn. Mater. 323(2011) 1827.[3] R. Mustafa Öksüzoğlu, Özlem Akman, Mustafa Yıldırım, Bekir Aktaş, Journal of Magnetics,17(4), 245-250 (2012).[4] K. O‘Grady, L.E. Fernandez-Outon, G. Vallejo-Fernandez, J. Magn. Magn Mater. 322 (2010)883.[5] Srinivas Polisetty, Sarbeswar Sahoo, and Christian Binek, Phys. Rev. B 76 (2007) 184423.[6] Andreas Biternas PhD-Thesis, ?Study of the training effect in exchange bias using the domainstate model?, University of York, Department of Physics (2009).[7] L.E. Fernandez-Outon, G. Vallejo-Fernandez, Sadia Manzoor1, K. O‘Grady, Journal ofMagnetism and Magnetic Materials 303 (2006) 296–301.[8] A. Kohn, J. Dean et al. Journal of Applied Physics 109 (2011) 083924.