2018年第65回応用物理学会春季学術講演会

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10 スピントロニクス・マグネティクス » 10.4 半導体スピントロニクス・超伝導・強相関

[20p-D104-1~11] 10.4 半導体スピントロニクス・超伝導・強相関

2018年3月20日(火) 13:00 〜 16:00 D104 (56-104)

好田 誠(東北大)、ファム ナムハイ(東工大)

14:45 〜 15:00

[20p-D104-7] Analysis of spin switching effect in GdN/NbN/GdN superconducting spin valves

Yota Takamura1,2、Juan Pedro Cascales1、Rafael Goncalves1,3、Gregory M. Stephen4、Donald Heiman4、Atilgan Altinkok1,5、Clodoaldo Irineu Levartoski de Araujo3、Biswarup Satpati6、Valeria Lauter7、Jagadeesh S. Moodera1 (1.MIT、2.Tokyo Tech、3.Federal Univ. of Vicosa、4.Northeastern Univ.、5.Giresun Univ.、6.Saha Inst. of Nuclear Phys.、7.Oak Ridge National Lab.)

キーワード:Spin switching effect, Superconductor

Superconducting spin valves (SSVs)1,2 consisting of a superconductor spacer sandwiched by two ferromagnetic insulators (FIs) attract considerable interest since the superconducting state can be manipulated by the relative magnetization configuration of the FI layers. This means that the infinite magnetoresistance ratio can actually be achieved in SSVs. This phenomenon, referred to as spin switching effect (SSE), is caused by the induced exchange field in the SC spacer from the adjacent FI layers and thus the interfaces between SC/FIs are very important. SSVs with a NbN spacer have the potential to exhibit SSE at relatively high temperatures,3 owing to high critical temperature (TC) of 16 K of NbN. Our group has demonstrated the first, perfect SSEs in GdN/NbN/GdN trilayer SSVs by atomic level optimization of the two interfaces, however, the observation temperature remained as low as 1.3 K4. In this talk, to clarify optimum interfaces for SSE, we quantitatively analyzed the induced exchange field in the SSVs using different two models and compare it to the interfacial magnetic moment evaluated from polarized neutron reflectivity (PNR) measurements.
SSVs of GdN(27nm)/NbN(3.5nm)/GdN(13nm) trilayers were formed with the reactive sputtering technique in a UHV system. The Gd monolayers were inserted between NbN/GdN interfaces to compensate the nitrogen less interfaces. SSE signals were clearly observed from 2.5 K down to 1.1 K. The anti-parallel (AP) state showed a TC of 1.7 K while in the parallel (P) state it was 1.4 K. An equivalent induced magnetic field was quantitatively estimated by the Kulic-Endres modelf. A pair breaking factor in the model which was evaluated from a ration ofTC in the P and AP states was enhanced by hundredfold by tailoring interfaces by the Gd insertion layers. In our presentation, we will discuss a relationship between pair breaking factors and interfacial magnetic moments analyzed by PNR.
This work was supported by NSF and ONR grants, JSPS, and Fundacion Seneca (19791/PD/15). The research conducted at the SNS is sponsored by the Scientific User Facilities Division, Office of BES, U.S. DOE.
References
1P.G. De Gennes, Phys. Lett. 23, 10 (1966).
2B. Li, N. Roschewsky, B.A. Assaf, M. Eich, M. Epstein-Martin, D. Heiman, M. Muzenberg, and J.S. Moodera, Phys. Rev. Lett. 110, 97001 (2013).
3Y. Zhu, A. Pal, M.G. Blamire, and Z.H. Barber, Nat. Mater. 16, 195 (2017).
4Y. Takamura et al., MMM conf., Pittsburgh, USA, GF-02, Nov. 2017