Interlayer Magnetic Coupling Interactions of Two Ferromagnetic Layers by Spin Polarized Tunneling

Abstract

Magnetic interactions involving ferromagnetic layers separated by an insulating barrier have been studied experimentally on a fully epitaxial hard-soft magnetic tunnel junction: Fe/MgO/Fe/Co. For a barrier thickness below 1 nm, a clear antiferromagnetic interaction is observed. Moreover, when reducing the MgO thickness from 1 to 0.5 nm, the coupling strength increases up to J=-0.26 erg.cm(-2). This behavior, well fitted by theoretical models, provides an unambiguous signature of the interlayer exchange coupling by spin-polarized quantum tunneling.

Multi-ferroic and magnetoelectric materials and interfaces

“…If the barrier is insulating the interlayer exchange, coupling is non-oscillatory and decays exponentially as a function of barrier thickness reflecting the evanescent nature of exchange-mediating states. For example, strong AFM coupling was reported in epitaxial Fe/MgO-Fe junctions [148,149]. Using an FE barrier allows the magnitude of the interlayer exchange coupling to be affected by FE polarization orientation [150].…”

Defect-Mediated Properties of Magnetic Tunnel Junctions

“…Unlike a metallic spacer layer, the tunneling barrier leads to nonoscillatory coupling which decays exponentially as a function of the barrier thickness [18], [19], [20], [21]. Experimental observations of IEC have been reported for only two systems-Fe-MgO-Fe [16] and Fe-Si-Fe [17]. In both cases large coupling strength is observed comparable to that of metallic spacers.…”

“…IEC in Fe-MgO-Fe MTJs was found to be AFM for small barrier thickness but changes sign for thicker barriers [16]. It is not clear, however, whether the switching is caused by magnetostatic interaction due to interface roughness or has intrinsic origin.…”

“…It should be pointed out that in [16] the coupling for larger barrier thickness approaches a finite value. This is attributed to the "orange peel" effect which given the quality of the sample is nearly constant at this thickness range.…”

“…Experimental observations of IEC across an insulator are still rare [17], [16]. The theoretical approaches to IEC are based either on the spin torque exerted by one ferromagnet on the other [18], [19] or the induced DOS in the spacer by the ferromagnets [20], [21].…”