Magnetic and thermal relaxation in (NiFe/CoFe)/PtMn and NiFe/NiMn bi-layers for spin valve heads.

The magnetic and thermal relaxation of exchange coupling, H[sub ex] in (NiFe/CoFe)/PtMn and NiFe/NiMn bi-layers has been studied as a function of temperature between 25 °C to 250 °C and magnetic field between 0 to 1000 Oe applied antiparallel to the original exchange coupling direction. The blocking temperature was about 380 °C for (NiFe/CoFe)/PtMn, and 410 °C for NiFe/NiMn. It was found that the H[sub ex] of the bi-layers decreased gradually with increasing time, while the coercivities remained almost a constant. The H[sub ex], measured at a temperature of 250 °C and a reversal field of 1000 Oe, decreased from 205 Oe to 0 and then changed its sign. The relaxation time, defined as the time required for H[sub ex] to reach zero, is about 3.1 h and 8.7 h for (NiFe/CoFe)/PtMn and NiFe/NiMn, respectively. The relaxation process for the bi-layers could be understood as the superposition of two exponential decays with different rates associated with a distribution of energy barriers. Spin valve heads using NiFe/NiMn bi-layers could be expected more stable, than those using (NiFe/CoFe)/PtMn bi-layers at an elevated operating temperature. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]