Tunneling in epitaxial Fe/Si/Fe structures with strong antiferromagnetic interlayer coupling

Abstract

Fe͑5 nm͒/Si͑0.8 -2 nm͒/Fe͑5 nm͒ structures are grown by molecular-beam epitaxy on Ag͑001͒ buffered GaAs substrates. Ferromagnetic tunneling junctions with crossed electrodes and junction areas ranging from 22 to 225 m 2 are patterned using photolithography. Antiparallel alignment of the magnetizations due to antiferromagnetic interlayer coupling, which is confirmed by longitudinal magneto-optical Kerr effect hysteresis loops, exists for the whole range of spacer thicknesses. Transport properties in current perpendicular to the sample plane geometry are examined by the four-point method in the temperature range from 4 K to room temperature. As a function of spacer thickness, the junctions show a strong increase of the resistance times area product from Ϸ1 ⍀ m 2 to more than 10 k⍀ m 2 . The dI/dVϪV curves are parabolic and asymmetric and thus characteristic for trapezoidal tunneling barriers. The mean barrier heights derived from Brinkman fits range from 0.3 to 0.8 eV. The zero-bias resistance of the tunneling junctions moderately decreases with temperature by less than 10% over the whole measured temperature range. All these transport properties fulfill the necessary and sufficient criteria for elastic tunneling.

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.…”

“…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].…”

Introduction to spin-polarized ballistic hot electron injection and detection in silicon

“…Although weak spin-valve effects are often presented, no evidence of spin precession is available so the signals measured are ambiguous at best [42,43]. Indeed, although magnetic exchange coupling across ultra-thin tunnelling layers of Si was seen, not even any spin-valve magnetoresistance was observed, [44] except with SiGe [45].…”

Thermal enhancement of the antiferromagnetic exchange coupling between Fe epilayers separated by a crystalline ZnSe spacer

“…Other semiconductor epitaxial systems such as (Ga,Mn)As/(Al,Ga)As/(Ga,Mn)As 13 and (In,Mn)/InAs/(In,Mn)As 14 are ferromagnetic exchange coupled for rather long spacer thickness range, typically around 30 nm. Strong antiferromagnetic coupling, exponentially decaying with the thickness of Si spacer has been observed for Fe/Si/Fe epitaxial structures 15 . However, the high chemical reactivity at the Fe/Si interfaces always complicates the physics of the system.…”