Masakazu Kobayashi1, 2, Su Nan1
1. Dept. EE & BS, Waseda University, Shinjuku, Tokyo, Japan.
2. Waseda University, Material Research Technology Institution, Shinjuku, Tokyo, Japan.
Masakazu Kobayashi1, 2, Su Nan1
1. Dept. EE & BS, Waseda University, Shinjuku, Tokyo, Japan.
2. Waseda University, Material Research Technology Institution, Shinjuku, Tokyo, Japan.
The proximity effect between a thin-film superconductor (S) and a ferromagnet (F) can lead to a spin-splitting of the quasiparticle density of states and suppression of the superconducting critical temperature (TC) (1). At an S/F interface,
the average magnitude of the spin-splitting in S can be tuned via the micromagnetic state of F with shifts in TC between magnetized (Tc,m) and de-magnetized (Tc,dm) ferromagnet states being
dependent [1-3] on the ratio of the superconducting coherence length (ξ) to the domain wall width (dw) ¾ i.e., (Tc,m- Tc,dm)/Tc,dm = ΔTC/Tc,dm µ ξ/dw can theoretically be infinite for an appropriate combination of S and F thin films in which S is thinner than ξ. Experimentally, however, such an absolute spin-valve effect is hard to achieve
with ΔTC/Tc,dm ratios tending to be a small fraction of Tc,dm, indicating physics beyond the standard picture of the S/F proximity effect. Here we report S/F bilayers and F/S/F spin-valves
in which F is an f-orbital ferromagnet (HoGd) with a controlled composition to tune the ratio of the orbital to spin components of the magnetization. The results demonstrate that ΔTC/Tc,dm can approach
infinity for a large ratio of the orbital moment to spin moment, which enables a near-absolute spin-valve effect. Our results demonstrate that the band structure of the ferromagnet in conjunction with the ξ/dw can be
tuned to enable high-performance superconducting memory for energy efficiency electronics. A first principle theory is required in order to understand the relationship between ΔTC / Tc,dm and the ratio
of the orbital to spin moment of the F metal.
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A Robinson, Phys. Rev. Lett. 121, 077003 (2018).