Blocking temperature distribution and long-term stability of spin-valve structures with Mn-based antiferromagnets

Abstract

We have determined the blocking temperature distribution Tb(T) in spin-valve sheet films with FeMn, IrMn, PtMn, NiMn and CrPdMn antiferromagnetic layers (AFM). We find a clear dependence of Tb(T) on the field applied during the measurement, which we link to the reversal state of the pinned layer through the torque applied on the AFM. Using fields large enough to fully reverse the pinned layer, NiMn and PtMn show little or no components of the blocking temperature below 150 °C, whereas both IrMn and CrPdMn (the latter in a “synthetic” AFM design) exhibit important low-temperature trailing edges of the distribution. Accelerated annealing experiments in a low reversed field equivalent to the self-demagnetizing field in a micron-size head allows us to access the time to failure and the failure activation energy from which the expected lifetime can be assessed. We find a general correlation between the expected lifetime and the fraction of loose (e.g., unblocked) AFM spins at any given temperature. Accordingly, only NiMn and PtMn are found to exhibit a sufficient long-term stability for disk-drive operations.

Influence of stress and unidirectional field annealing on structural and magnetic performance of PtMn bottom spin-filter spin valves

“…In Spin valve (SV) recording heads a sufficient exchange interaction field H ex between an antiferromagnetic (AFM) pinning layer and a ferromagnetic (FM) pinned layer is required to keep the pinned layer's magnetization unchanged during manufacturing and at operating temperature of the giant magneto-resistive (GMR) reader [1]. Antiferromagnetic PtMn films have gained increasing attention because of their high blocking temperature [2,3] and high H ex , which amounts in small sensor dimensions and high reliability for higher recording densities [4].…”

Theoretical study of the blocking temperature in polycrystalline exchange biased bilayers

“…A large AF grain suggests large energy barriers for the grain. It is well known that it is hard to determine experimentally the blocking temperature in polycrystalline bilayers since the exchange bias decreases gradually with temperature to zero [4]. Fig.…”

“…It is natural to think that T B should be related to the Ne´el temperature T N of the AF. However, T B has been found to be lower than T N : For some FM/ AF bilayers such as NiFe/NiMn the difference can be more than 400 1C [4]. T B has also been found to decrease with decreasing AF thickness [5][6][7][8][9][10] and to decrease with decreasing AF grain size.…”

Exchange bias in epitaxial and polycrystalline thin film Ru2MnGe/Fe bilayers

“…The exchange bias in epitaxial films shows a significantly higher thermal stability up to 130 K. The exchange energies at 3 K of J ¼ 0.238 erg/cm 2 (epitaxial) and J ¼ 0.189 erg/cm 2 (polycrystalline) are of the same order as for common exchange bias systems at room temperature, for example, 0.18 erg/cm 2 for PtMn/CoFe and IrMn/CoFe. 24 The temperature stability, however, needs to be improved for applications. Finally, the exchange bias field in polycrystalline samples could be improved noticeably by adding an intermediate Mn layer of 1-2 monolayers thickness in the case of polycrystalline samples.…”