碩博班專題討論(Colloquium)
Spin Hall magnetoresistance and finite size e4ects in multiferroic BiFeO3 thin films
演講者 : Prof. Daniel Sando - (School of Physical & Chemical Sciences, University of Canterbury, New Zealand)
演講地點 :
理學教學新大樓物理系1F 36102教室
演講時間 :
2024 / 09 / 20
14:10
Bismuth ferrite (BiFeO3; BFO) is a room temperature multiferroic with coexisting ferroelectric and magnetic orders. As an epitaxial thin film, different levels of substrate-imposed strain can induce BFO to form in either a tetragonal (T)-like or rhombohedral (R)-like phase1. Recently, BFO – an antiferromagnet (AFM) with weak ferromagnetism (FM) – has garnered significant attention for its magnonic (spin wave) response, with various studies investigating the effect of domain walls on spin wave propagation2. However, in BFO thin films, it is still not clear how strain-induced structural changes influence the magnonic behavior. At the same time, the influence of finite size (i.e., thickness reduction) on the AFM order parameter in BFO films remains unknown.
In this presentation, I will report our recent results on the influence of substrate strain and finite size effects on the magnetic order of BFO thin films. We first use spin Hall magnetoresistance (SMR) measurements on Pt-BFO thin film heterostructures to reveal that the BFO surface magnetic state is dramatically different for the T-like vs. R-like ferroelectric structural phases3. SMR consistent with weak ferromagnetism for both R-like BFO and T-like BFO is found, albeit with markedly different temperature dependencies. For T-like BFO, the SMR is enhanced at room temperature, and decays with reduced temperatures. By contrast, R-like BFO shows a monotonic decrease in SMR response with increasing temperature, mirroring the trend of the weak FM moment of BFO.
Second, using conversion electron Mössbauer spectroscopy to measure ultrathin T-like BFO films4, we find a finite scaling effect whereby the AFM transition (Néel) temperature TN decreases from ~320 K at a thickness of 50 nm to ~280 K at 9 nm, as also evidenced also by the strength of magnetic hyperfine field BHF. At the same time, we observe no influence of the finite size on the ferroelectric order parameter. Our results have implications for the integration of BFO thin films in future nanoscale magnonic and spintronic devices.
References
1. Sando, D., Xu, B., Bellaiche, L. & Nagarajan, V. A multiferroic on the brink: uncovering the nuances of strain-induced transitions in BiFeO3. Appl Phys Rev 3, 011106 (2016).
2. Parsonnet, E. et al. Nonvolatile Electric Field Control of Thermal Magnons in the Absence of an Applied Magnetic Field. Phys Rev Lett 129, 087601 (2022).
3. Sando, D. et al. Strain-dependent spin Hall magnetoresistance in the multiferroic antiferromagnet BiFeO3. Phys Rev Mater 8, L071401 (2024).
4. Sando, D. et al. Finite Size Effects in Antiferromagnetic Highly Strained BiFeO 3 Multiferroic Films. Advanced Physics Research 2400068 (2024) doi:10.1002/apxr.202400068.
In this presentation, I will report our recent results on the influence of substrate strain and finite size effects on the magnetic order of BFO thin films. We first use spin Hall magnetoresistance (SMR) measurements on Pt-BFO thin film heterostructures to reveal that the BFO surface magnetic state is dramatically different for the T-like vs. R-like ferroelectric structural phases3. SMR consistent with weak ferromagnetism for both R-like BFO and T-like BFO is found, albeit with markedly different temperature dependencies. For T-like BFO, the SMR is enhanced at room temperature, and decays with reduced temperatures. By contrast, R-like BFO shows a monotonic decrease in SMR response with increasing temperature, mirroring the trend of the weak FM moment of BFO.
Second, using conversion electron Mössbauer spectroscopy to measure ultrathin T-like BFO films4, we find a finite scaling effect whereby the AFM transition (Néel) temperature TN decreases from ~320 K at a thickness of 50 nm to ~280 K at 9 nm, as also evidenced also by the strength of magnetic hyperfine field BHF. At the same time, we observe no influence of the finite size on the ferroelectric order parameter. Our results have implications for the integration of BFO thin films in future nanoscale magnonic and spintronic devices.
References
1. Sando, D., Xu, B., Bellaiche, L. & Nagarajan, V. A multiferroic on the brink: uncovering the nuances of strain-induced transitions in BiFeO3. Appl Phys Rev 3, 011106 (2016).
2. Parsonnet, E. et al. Nonvolatile Electric Field Control of Thermal Magnons in the Absence of an Applied Magnetic Field. Phys Rev Lett 129, 087601 (2022).
3. Sando, D. et al. Strain-dependent spin Hall magnetoresistance in the multiferroic antiferromagnet BiFeO3. Phys Rev Mater 8, L071401 (2024).
4. Sando, D. et al. Finite Size Effects in Antiferromagnetic Highly Strained BiFeO 3 Multiferroic Films. Advanced Physics Research 2400068 (2024) doi:10.1002/apxr.202400068.
