Oliver Paull, PhD student, UNSW
Interactions at interfaces of magnetic materials such as giant magnetoresistance (GMR) form the physical foundation of many technological devices in today’s market. Although GMR technlogies are now somewhat dated, interactions at the interface between layers of oxide materials continue to demonstrate attractive mechanisms for technology applications due to the wide variety of available oxide materials as well as their ability to be well lattice-matched to form heterostructures.
Magnetic thin-film superlattices made of 15 repetitions of La2/3Sr1/3MnO3 (LSMO) and LaNiO3 (LNO) have been shown to exhibit a magnetic exchange interaction in LNO that is dependent upon it’s thickness n (where n is the number of unit cells of LNO) between LSMO layers [1]. At n=1, the LSMO layers are ferromagnetically aligned with eachother. At n=3 however, the LSMO layers are canted by 110 degrees with respect to one another. This canting is reportedly driven by an emergent c-axis spin-helix in LNO that arises due to charge transfer at the interfaces between LNO and LSMO [2].
We have fabricated superlattices of similar quality using Reflected High Energy Eectron Diffraction (RHEED) assisted Pulsed Laser Deposition (PLD), where RHEED is used to ensure unit-cell precision in layer thicknesses. These superlattices have been designed so they exhibit n=3 and n=1 interactions within the same superlattice in a modulated pattern. This modulation of the effective LNO exchange interaction in these samples creates a toy model of coupled magnetic layers to explore. The modulated design of these samples create “frustrated” environments where the effective exchange interaction is different on each side of an LSMO layer within the superlattice. We utilise polarised neutron reflectometry using PLAYPUS to reveal the complex magnetic profile of these modulated superlattices by measuring the non-spin-flip (R++, R—), and spin-flip (R+-, R-+) cross sections. Presented are the current progress and prospects in the fitting process of these complex datasets.
[1] J. Hoffman et al. Phys. Rev. X 6, 041038 (2016) [2] G. Fabbris et al. Phys. Rev. B 98, 180401(R) (2018)About the presenter
Oliver is a PhD student studying with Nagarajan Valanoor (UNSW). Oliver specialises in fabrication and characterisation of thin film heterostructures. He uses pulsed laser deposition (PLD) and laser molecular beam epitaxy (LMBE) to fabricate the desired materials, and uses high-resolution X-ray diffraction, piezoresponse force microscopy (PFM), magnetometry and neutron scattering in characterization of the materials.
In terms of FLEET research themes, my research falls under theme 1 and technology A. The end goal for my FLEET project is to develop artificial graphene by interfacing a well-known 2D-electron gas (2DEG) system with a multiferroic material who’s ferroelectric polarisation can tune the resistance of the underlying 2DEG.