Controllable Josephson current through a pseudospin-valve structure

Abstract

A thin Co/Cu/Permalloy (Ni80Fe20) pseudo-spin-valve structure is sandwiched between superconducting Nb contacts. When the current is passed perpendicular to the plane of the film a Josephson critical current (IC) is observed at 4.2 K, in addition to a magnetoresistance (MR) of ∼ 0.5 % at high bias. The hysteresis loop of the spin-valve structure can be cycled to modulate the zero field IC of the junction in line with the MR measurements. These modulations of resistance and IC occur both smoothly and sharply with the applied field. For each type of behaviour there is a strong correlation between shape of the MR loops and the IC modulation. PACS numbers: 74.50+r, 75.47.De, 85.25.Cp,

Characteristics of strong ferromagnetic Josephson junctions with epitaxial barriers

“…10 In these cases the junctions are much more sensitive to the barrier properties and d F , and hence the 0 − π crossover has not been demonstrated in junctions with strong ferromagnetic barriers.…”

Controllable 0–π Josephson junctions containing a ferromagnetic spin valve

“…Imagine now a Josephson junction with the structure S/F 1 /N/F 2 /S, where F 1 and F 2 may be different ferromagnetic materials [14][15][16][17] . The pair correlation function describing Cooper pairs from the left-hand S accumulates a phase φ 1 = Q If, however, the magnetization of F 2 is antiparallel to that of F 1 , then the role of majority and minority bands is reversed, and the pair correlation function will acquire the opposite phase, −φ 2 .…”

“…Phase-controllable Josephson junctions have applications in superconducting electronics based on single-flux-quantum logic. The most obvious application is in superconducting memory [14][15][16][17] . A single S/F/S Josephson junction with controllable critical current amplitude could function as a superconducting memory cell, but one must find a way to address such a memory cell when it is embedded in a large memory array, and the speed at which the junction switches into the voltage state after the 'read' current is applied is limited by the small I c R N product of the junction.…”

Spacerless metal-manganite pseudo-spin-valve structure

“…This was in contrast to the negative MR obtained from LSMO\NiFe system studied by Ruotolo et al Whether the observed GMR is positive or negative is known to be dependent on the relative sign of spin polarization in the neighboring magnetic layers: 18 Materials with opposite signs of spin polarizations have different majority spin bands, which lead to contrasting scattering probabilities for opposite spin populations when their magnetization vectors are aligned. This leads to a high resistive state at high magnetic field and hence a positive MR. 19 However, negative MR behavior has been reported for NiFe-Co ͑or CoFe͒ spin valves 20 and tunnel junctions, 21 and the two types of alloys should possess the same sign of spin polarization. 18 It is therefore expected that the same sign of MR would appear in LSMO\NiFe and LSMO\CoFe spin valves.…”