Engineering Magnetic Anisotropy and Emergent Multidirectional Soft Ferromagnetism in Ultrathin Freestanding LaMnO3 Films

Published

May 24, 2022

Author(s)

Qinwen Lu, Zhiwei Liu, Qun Yang, Hui Cao, Purnima P. Balakrishnan, Qing Wang, Long Cheng, Yalin Lu, Jian-Min Zuo, Hua Zhou, Patrick Quarterman, Shinichiro N. Muramoto, Alexander Grutter, Hanghui Chen, Xiaofang Zhai

Abstract

Owing to their small coercive fields and weak magnetic anisotropy, soft ferromagnetic films are extremely useful for nanoscale devices that need to easily switch spin directions. However, they are rare, particularly when a film thickness is reduced to a few nanometers and various anisotropic interactions – such as magnetocrystalline, shape, or magnetoelastic – compete. Here, we synthesize large-area, high-quality, ultrathin freestanding LaMnO3 films on Si and find unexpected soft ferromagnetism both along the in-plane and out-of-plane directions when the film thickness is reduced to 4 nm. We argue that the vanishing magnetic anisotropy between the two directions is a consequence of two coexisting magnetic easy-axes in different atomic layers of the LaMnO3 film. Spectroscopy measurements reveal a large Mn valence variation in LaMnO3 thin films from 3+ in the bulk-like interior to approximately 2+ in both surface regions where considerable hydrogen infiltration occurs due to the water dissolving process. First-principles calculations show that protonation of LaMnO3 decreases the Mn valence and switches the magnetic easy-axis from in-plane to out-of-plane as Mn valence approaches 2+ from its 3+ bulk value. Our work demonstrates that ultrathin freestanding films can exhibit new functional properties that are absent in homogeneous materials, concomitant with their convenient compatibility with Si-based devices.

Citation

ACS Nano

Volume

16

Issue

5

Pub Type

Journals

Keywords

Thin film, Membrane, Magnetism, Oxide

Citation

Lu, Q. , Liu, Z. , Yang, Q. , Cao, H. , Balakrishnan, P. , Wang, Q. , Cheng, L. , Lu, Y. , Zuo, J. , Zhou, H. , Quarterman, P. , Muramoto, S. , Grutter, A. , Chen, H. and Zhai, X. (2022), Engineering Magnetic Anisotropy and Emergent Multidirectional Soft Ferromagnetism in Ultrathin Freestanding LaMnO₃ Films, ACS Nano (Accessed April 19, 2024)