Surface-sensitive magnetic characterization technique for ultrathin ferromagnetic film with perpendicular magnetic anisotropy

Yi Wan,Lun Dai,Mingzhu Xue,Shiqi Yang,Yuxuan Peng,Erjun Kan,Pan Li,Mingyan Liu,Jinbo Yang,Xing Cheng

doi:10.1063/5.0012321

Abstract

Ultrathin ferromagnetic films display a wealth of spectacular characteristics, one of which is that two-dimensional ferromagnetism is stabilized exclusively by magnetic anisotropies. In this work, we experimentally demonstrated the realization of ultrathin yttrium iron garnet (Y3Fe5O12) films with perpendicular magnetic anisotropy by pulsed laser deposition. A labyrinthine magnetic domain configuration in Y3Fe5O12 was identified by magnetic force microscopy, qualitatively determining that the magnetic moment possesses an out-of-plane component. Magnetic moments in the Y3Fe5O12 film were investigated by using a vibrating sample magnetometer and magnetic circular dichroism spectroscopy. Due to the surface sensitivity, the characterization technique based on magnetic circular dichroism spectroscopy presents as a high-resolution magneto-optical method to determine the magnetic property quantitatively, which has an advantage over the vibrating sample magnetometer technique commonly used for bulk crystals or powders, especially when the paramagnetic background from the supporting substrate is non-negligible. Our work introduces the burgeoning material synthesis and processing technology, and miscellaneous characterization techniques into the study of conventional magnetic oxide films, providing powerful supplements to the detection and modulation of magnetism at the nanoscale.

Highlights

Ferromagnetic or ferrimagnetic insulating materials have played a significant role in spintronics because they allow spin current flow without charge transport, offering a unique platform for low energy dissipation information transmission and processing1–3 and probing spin-current effects, such as spin pumping,4 spin-transfer torque,5 spin Hall magnetoresistance,6,7 and the spin Seebeck effect.8–10 As one of the most thoroughly studied ferrimagnetic insulators, yttrium iron garnet [Y3Fe5O12 (YIG)]11,12 has been extensively investigated in regard to its enormous properties, such as high Curie temperature, exceptionally low dielectric loss, and narrow line width at GHz frequencies, as a promising candidate for spin pumping and thermally driven spin caloritronics.13–18 For simplification purposes, we will refer to the YIG as ferromagnetic later in this article
The YIG thin-films with the nanoscale thickness were successfully synthesized by pulsed laser scitation.org/journal/adv deposition (PLD)20–22 and magnetron sputtering23 for their advantages over liquid phase epitaxy in thickness control
If the net magnetic moments in YIG ultrathin films are insufficiently large at extremely low temperature, the surface-insensitive vibrating sample magnetometer (VSM) technique will not enable the acquisition of the hysteresis loop information

Summary

Introduction

Ferromagnetic or ferrimagnetic insulating materials have played a significant role in spintronics because they allow spin current flow without charge transport, offering a unique platform for low energy dissipation information transmission and processing1–3 and probing spin-current effects, such as spin pumping,4 spin-transfer torque,5 spin Hall magnetoresistance,6,7 and the spin Seebeck effect.8–10 As one of the most thoroughly studied ferrimagnetic insulators, yttrium iron garnet [Y3Fe5O12 (YIG)]11,12 has been extensively investigated in regard to its enormous properties, such as high Curie temperature, exceptionally low dielectric loss, and narrow line width at GHz frequencies, as a promising candidate for spin pumping and thermally driven spin caloritronics.13–18 For simplification purposes, we will refer to the YIG as ferromagnetic later in this article. We synthesized the YIG films with the perpendicular easy magnetization axis based on the strain-induced anisotropy by the PLD method.22 Abundant characterization techniques, including magnetic force microscopy (MFM), vibrating sample magnetometer (VSM), and magnetic circular dichroism (MCD)

Results

Conclusion