Measurement of the coupling strength distribution in ferromagnetic (F)/antiferromagnetic (AF) exchange bias systems

Abstract We propose a method for determination of the distribution function P ( j ) of the coupling energy density j in polycrystalline textured ferromagnetic (F)/antiferromagnetic (AF) film systems. P ( j ) governs the entire film coupling J and the exchange bias field H e and was not measurable until now. The method is verified by torquemetry in a high magnetic field and by reversing its rotation sense. The transition to a new magnetic steady state after rotation reversal is analyzed within a Stoner–Wohlfarth model including thermal relaxation. This transition is completed earlier for strongly coupled grains than for grains with smaller j , which is reflected in the torque curves. We determined P ( j ) for a sputtered NiFe(16 nm)/IrMn(0.8 nm) film at T =50 K in the hysteretic range of coupling energies and found that P strongly decreases for increasing j .