Abstract:

Nowadays, Ferromagnetic/Superconducting/Ferromagnetic trilayers (FM/SC/FM TLs) are intensively studied. Here, based on (CoO-) Co/Nb/Co TLs of thin Nb interlayer (below 30 nm) we introduce two classes of low-T-c SC-based cryogenic devices, depending on the thickness of the Co outer layers and the presence of a CoO underlayer. An extended range of Co thickness (from 10 to 80 nm) was investigated and an underlayer of CoO was selectively employed, practically aiming to control in-plane and out-of-plane magnetization processes through utilization of shape anisotropy and exchange bias. To this effect magnetic force microscopy, magnetization and magnetoresistance data are presented. Ancillary atomic force microscopy and Rutherford back scattering data are presented, as well. CoO-Co/Nb/Co TLs of the first class have thin Co outer layers (10-30 nm) and are further assisted by the presence of a CoO underlayer to behave as efficient spin valves (Delta R/R-nor = 1.5% and Delta R/R-min = 2.4%) under the action of the FMs in-plane exchange fields; the effect is termed superconducting Spin-Valve Effect (sSVE). Co/Nb/Co TLs of the second class have thick Co outer layers (50-80 nm) and without the need of a CoO underlayer act as almost absolute supercurrent switches (Delta R/R-nor = 97.7% and Delta R/R-min = 28000%) under the action of FMs out-of-plane stray fields; the effect is termed superconducting Magneto-Resistance Effect (sMRE). The properties of these (CoO-) Co/Nb/Co TLs resemble the behavior of standard FM/normal-metal/FM and FM/insulator/FM TLs that exhibit the effects giant (GMR) and tunnel (TMR) magnetoresistance, respectively. Aiming to utilize the FM/SC/FM TLs studied here into cryogenic applications we thoroughly surveyed their operational H-T phase diagram and discuss how can be used to realize binary ('0'-'1') elemental devices for information management in both read heads and memory units. The underlying physical mechanisms responsible for the sSVE and sMRE observed in the two different classes of TLs, that is CoO-Co/Nb/Co and Co/Nb/Co, respectively and the technical requisites that the SC and FM ingredients should meet are discussed.