Field-free spintronic terahertz emitters based on IrMn/Fe/Pt exchage bias heterostructures

Zhao-Zhao Zhu,Zheng Feng,Jian-Wang Cai

doi:10.7498/aps.71.20211831

Abstract

Spintronic terahertz (THz) emitter has more advantages such as lower cost, broader spectrum and easier operation than the commercial THz emitters, and thus has become a focus of research towards the next-generation THz source. However, in such a spintronic THz emitter, an external magnetic field is technologically required to align the orientation of the magnetization, which is detrimental for practical applications. Here, a spintronic terahertz emitter based on IrMn/Fe/Pt exchange bias structure is presented. By means of ultrafast spin injection on Fe/Pt interface followed by the spin-to-charge conversion in Pt, plus the effective magnetic field originating from the IrMn/Fe interface, the THz pulse with considerable intensity can be generated in such a structure without the assistance of external field. Besides, the remanent magnetization for thin Fe layer is enhanced by inserting an ultrathin Cu layer between the IrMn surface and the Fe surface, which is beneficial to the field-free THz emission. The range of obtained dynamic THz spectrum exceeds 60 dB and the positive saturation field can reach up to ~ –10 mT by optimizing the multilayer thickness, meeting the standard for commercial application. By rotating the sample, it is found that the polarization direction of the generated THz wave circulates simultaneously and keeps perpendicular to the direction of exchange bias field in the film plane. Moreover, we design a spin valve THz emitter based on the structure of IrMn/Fe/Pt/Fe by adding a free ferromagnetic Fe layer into the exchange bias multilayers. The emitted THz pulse amplitude is larger for the antiparallel alignment of the Fe layers at zero field than for the parallel alignment or exchange bias structure. The present work shows that the spin terahertz emitter based on IrMn/Fe/Pt exchange bias structure can produce the considerable terahertz signals without external field. Furthermore, the polarization direction of the emitted THz signal can be easily manipulated by rotating the sample. Because of this series of advantages, such exchange bias heterostructures are expected to play an important role in designing the next-generation THz source.

Highlights

an external magnetic field is technologically required to align the orientation of the magnetization
which is detrimental for practical applications
a spintronic terahertz emitter based on IrMn

Summary

Introduction

关键词:太赫兹, 交换偏置, 超快自旋输运, 磁性异质结构 PACS:87.50.U, 85.75.–d, 75.78.Jp, 72.25.Rb Ess 1 引言 r 太赫兹 (THz) 波是指频率从 0.1—10 THz, 介 P 于毫米波与红外光之间的电磁波. 在 IrMn 和 Fe 的界面中插入超薄的 Cu, 可以使 Fe 在厚度很薄时具有 100% 的剩余磁化强度, 从而使其在无场下的太赫兹发射效率进一步提升, 并且其正向饱和场最高可达–10 mT, 远高于地磁场. (a) Illustration of the layer stacking and THz excitation configuration; (b) M-H loops for the MgO(111)/Pt(1.5 nm)/ IrMn(6 nm)/Fe(1.5 nm)/Pt(1.8 nm) (black line) and MgO (111)/Pt(1.5 nm)/IrMn(6 nm)/Cu(0.4 nm)/Fe(1.5 nm)/Pt (1.8 nm) (red line) on the applied in-plane magnetic field parallel to the exchange bias direction.

Results

Conclusion