Antiferromagnet Thickness Dependence of the Training Effect in Exchange-Coupled CoFe/MnIr Bilayers

The antiferromagnet thickness dependence of the net training effect is studied in exchange-coupled CoFe/MnIr bilayers. The maximum net training effect is observed near the critical thickness of the antiferromagnetic layer. The easy-axis redistribution of the unpinned antiferromagneic grains is explained by the two cycles of ferromagnetic-resonance measurement. The linear relationship between the net training effect and rotational hysteresis loss directly confirms that the training effect in ferromagnetic/antiferromagnetic bilayers originates from the reorientation of the unpinned antiferromagnetic grains from initial alignment to the final random state during consecutive cycles of hysteresis loops measurement.