Large Exchange Bias IrMn/CoFe for Magnetic Tunnel Junctions

We report on the enhancement of the exchange field, Hex , in IrMn/CoFe systems as a result of the application of field annealing procedures. The exchange field is enhanced up to a 37% on application of a 2 Tesla field for 90 minutes at 225degC. This setting process improves the magnitude of HEX without significant changes in the coercivity, HC, or the median blocking temperature. The sample with largest exchange bias field measured, 3.7 kOe and HC = 0.2 kOe at 20degC, seems to have the largest ratio of HEX to HC ever reported for an IrMn/CoFe exchange bias system. This makes these structures good candidates as pinned layers in magnetic tunnel junctions. The samples show good thermal stability with median blocking temperatures up to 200degC. The results also indicate that the improvement in the quality of the interfaces via the degree of alignment of the interfacial spins improves the coupling across the interface and hence the magnitude of the exchange bias field.

[1]  K. O’Grady,et al.  Antiferromagnetic grain volume effects in metallic polycrystalline exchange bias systems , 2008 .

[2]  K. O’Grady,et al.  Interfacial spin effects on Hex in metallic polycrystalline exchange biased systems , 2008 .

[3]  K. O’Grady,et al.  Measurement of the anisotropy constant of antiferromagnets in metallic polycrystalline exchange biased systems , 2007 .

[4]  M. Tsunoda,et al.  Large Exchange Bias and High Blocking Temperature of MgO-Barrier-MTJs With L1$_{2}$-Ordered Mn$_{3}$Ir , 2007, IEEE Transactions on Magnetics.

[5]  Hans Jurgen Richter,et al.  The transition from longitudinal to perpendicular recording , 2007 .

[6]  A. Johnston,et al.  Transmission electron microscopy study of CoFe films with high saturation magnetization , 2006 .

[7]  P. Freitas,et al.  Exchange bias in ordered antiferromagnets by rapid thermal anneal without magnetic field , 2005 .

[8]  K. O’Grady,et al.  Preparation of high moment CoFe films with controlled grain size and coercivity , 2005 .

[9]  S. Dijken,et al.  Influence of the annealing field strength on exchange bias and magnetoresistance of spin valves with IrMn , 2005 .

[10]  M. Takahashi,et al.  Giant exchange anisotropy observed in Mn–Ir∕Co–Fe bilayers containing ordered Mn3Ir phase , 2004 .

[11]  M. Carey,et al.  Thermal phenomena in IrMn exchange biased systems , 2004 .

[12]  Y. Huai,et al.  Effect of underlayer roughness, grain size, and crystal texture on exchange coupled IrMn/CoFe thin films , 2000 .

[13]  H. Tong,et al.  Studies on antiferromagnetic/ferromagnetic interfaces , 2000 .

[14]  R. Chantrell,et al.  Time dependent magnetisation in systems with distributed energy barriers , 1993 .

[15]  W. Meiklejohn,et al.  New Magnetic Anisotropy , 1956 .

[16]  K. O’Grady,et al.  Factors Affecting Exchange Bias in Polycrystalline Metallic Thin Films , 2007 .