Free tuning of exchange bias via resettable alignment of antiferromagnetic Néel axes using mechanical vibrations

Absence of net magnetization in antiferromagnet (AFM) renders magnetic anisotropy of AFM firmly robust against external magnetic field. Therefore, uniaxial realignment of spin structure in AFM requires the field-cooling procedure, which heats AFM to above Néel temperature overcoming the existing anisotropy followed by cooling in a magnetic field to reinstate its anisotropy. Ferromagnet (FM) coupled to the uniaxially aligned AFM spins exhibits unidirectional anisotropy, which is conventionally reflected in the exchange bias effect along the cooling-field direction. Here, we report that alternating mechanical vibrations with relatively low frequencies in the range of few kHz can substitute the inconvenient heating step in the conventionally well-known field-cooling process for the spin alignment of AFM. Mechanical vibration and external magnetic field have been applied simultaneously to AFM IrMn₃/FM Co or CoFeB bilayers deposited on Pb(Mg_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ (PMN-PZT) piezoelectric single-crystalline substrate in an ambient temperature. Exchange bias of the bilayers can arbitrarily be set along a desired direction as determined by the applied magnetic field. The simple technique without a heating step enables local control of exchange bias effect at selected regions only within complex microdevice structures. Furthermore, the capability of repeated post-readjustment of exchange bias effect in various directions and magnitudes would promote wider integrations of exchange-biased system in novel magnetic devices.