Abstract
The current flowing through a Mott spin junction depends on the relative spin orientation of the two ferromagnetic layers comprising the “source” and “drain” sides of the junction. The resulting current asymmetry is detected as giant or tunnelling magnetoresistance depending on whether the two ferromagnets are separated by a metal or an insulator. Based on the fundamental principles of reciprocity for spin-dependent electron scattering, one can envisage a one-magnet-only spin junction in which the source is non-magnetic, and the spin information is encoded by the spin polarisation of the electrons that have crossed or are backscattered from the drain magnetic layer. The practical significance of using an unpolarised source is that the state of the magnetic layer can be modified without affecting the process of probing it. Whether this reciprocity is realised in the actual junctions is not yet known. Here, we demonstrate a nano-sized, one-magnet-only Mott spin junction by measuring the finite spin polarisation of the backscattered electrons. Based on this finding, we conclude that since the junction acts as a spin filter, the magnetic layer must experience a spin transfer that could become detectable in view of the high current densities achievable in this technology.
Highlights
In Mott spin junctions, the source is used to establish a reference spin state[1]
The spin signal is encoded in a quantity, namely, the spin polarisation of the electron system, that cannot be detected, especially if the electrons are buried within a junction
The spin information is encoded in two further electronic systems, the backscattered electrons[8]
Summary
The present experiment uses a pair of Helmholtz coils that produce an external magnetic field pulse of variable strength (up to ≈ 10−1 T) along the positive and negative x-directions (Fig. 3a) with a controlled time structure. This is the key technical feature introduced to eliminate any instrumental asymmetry not related to the sought-for spin polarisation and with it the topographic cross-talk that rendered a previous study[17] inconclusive. If the spatial origin of the backscattered electrons is kept constant while the hysteresis curve is measured (Figs 2 and 3), we can eliminate instrumental asymmetries by averaging over the magnetic field.
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