EuS/Ta异质结的极大磁电阻效应

在铁磁/超导异质结中,铁磁体的交换场通过近邻效应将导致超导体准粒子态密度的塞曼劈裂.基于该效应,在外磁场不强的情况下,通过外加磁场可以有效地调节铁磁/超导界面处的交换作用,从而实现超导体在正常态和超导态之间转换,产生极大磁电阻.本文利用脉冲激光沉积方法制备了EuS/Ta异质结并研究了其电磁特性.Ta在3.6 K以下为超导态,EuS在20 K以下为铁磁态.在2 K时,EuS/Ta异质结中可观测蝴蝶型磁滞回线,证明在低磁场下(<±0.18 T)异质结中EuS铁磁态和Ta超导态共存.磁输运测试表明,通过施加外磁场可以有效调节EuS的交换场,随着交换场的增大,同时也加强了界面处的交换作用,从而抑制Ta的超导态,实现了Ta在超导态和正常态之间的转变,在EuS/Ta异质结中观测到了高达144000%的磁电阻.本文制备的EuS/Ta异质结具有极大磁电阻效应,在自旋电子学器件中有潜在的应用前景.

Infinite magnetoresistance of EuS/Ta heterostructure

Based on the proximity effect,the exchange interaction at the interface between a ferromagnetic insulator(FI)and a superconductor(S)could enhance the Zeeman splitting of the superconducting quasiparticle density of states.The superconducting electrons feel the exchange field on the surface of the S layer.Therefore,tuning the internal exchange field at the FI/S interface could switch the superconductor from a superconducting state to a normal state,leading to an infinite magnetoresistance in FI/S heterostructure.Here in this work,we fabricate the EuS/Ta heterojunction by the pulsed laser deposition,and perform the magnetotransport measurements.In the EuS/Ta heterojunction,Ta film as a typical BSC supercenter exhibits the superconducting transition under 3.6 K,and the EuS film is ferromagnetic under 20 K.The magnetization of EuS is suppressed by superconductivity of Ta at 0.01 T below 3 K.In addition,the butterfly-type hysteresis loop is observed at 2 K.And the decrease of the saturation magnetization of EuS/Ta heterostructure is observed by comparing with the EuS single layer.It is caused by a reconstruction of homogeneous ferromagnetic order in the EuS ferromagnetic layer due to the proximity effect with the Ta superconducting layer.The above measurement results show that the competition between the ferromagnetism of EuS film and superconductivity of Ta film below Tc of Ta film.If the exchange field of the FI is sufficiently strong,it tries to align the spins of the electrons of a Cooper pair in S layer parallel to each other,thus destroying the superconductivity.Meanwhile,the superconductivity in S layer will be recovered when the exchange field of the FI is weak.The resistance at a specific value of the magnetic field(1 T)steeply drops to zero,and clear hysteresis behavior is observed in EuS/Ta heterostructure,resulting in an infinite magnetoresistance up to 144000%,by tuning the internal exchange field at EuS/Ta interface.Meanwhile,the anomalous Hall effect with hysteresis behavior is observed at 2 K,indicating that the electron in Ta film is spin polarized due to the magnetic proximity effect near the EuS/Ta interface.Our results show that the EuS/Ta heterostructure with infinite magnetoresistance could be a good candidate for spintronic devices.