The relationship between the transformation kinetics and exchange field development in PtMnCr/NiFe bilayers

PtMnCr and other ordered tetragonal alloys used as antiferromagnetic pinnin g layers are in a nonmagnetic, disordered FCC phase upon deposition. In ord er to induce the FCT antiferromagnetic L10 ordered phase, a high temperatur e anneal must be performed. In PtMnCr, the ordered phase can nucleate and g row in either a (111) textured or random orientation. (111) textured growth of the FCT phase results in a shift in the PtMnCr (111) Bragg angle, while random growth results in a decrease in intensity of the peak. In addition, the random growth causes an increase in the intensity of the PtMnCr (111) peak detected off axis using low angle X-ray diffraction, Using this, the r elationship between the transformation kinetics and development of the exch ange field is studied in detail with X-ray and TEM, It is found that the de velopment of exchange held depends on three stages of the ordering transfor mation: (1) a nucleation period in which no exchange field develops, (2) gr owth of the ordered phase, in which the exchange field develops in proporti on to the FCT phase formed at the interface, and (3) a period in which the coercivity increases after the bulk transformation has completed. The mecha nisms responsible for this behavior are discussed.