Introduction
An international group of academic researchers have used PI-KEM LSAT substrates to explore the magnetic properties and interlayer coupling of ferromagnetic oxide thin films. The research was led by PhD student Jörg Schöpf from the University of Cologne, supervised by Ionela Lindfors-Vrejoiu, with contributions from colleagues at Lawrence Berkeley National Laboratory, Duke University, North Carolina State University and Aalto University.
After struggling to find a consistent source for high-quality (LaAlO3)0.3-(Sr2TaAlO6)0.7 (LSAT) crystals, the group began working with PI-KEM in 2024. Since then, several LSAT substrates have been supplied, which were all successfully used for epitaxy of ferromagnetic layers. Subsequently, the group published their research Tuning the interlayer coupling in La0.7Sr0.3Mn0.95Ru0.05O3 / LaNiO3 multilayers with perpendicular magnetic anisotropy. They have since ordered DyScO3 substrates for use in future research.
The Research
Understanding, and subsequently controlling, the magnetic properties of materials is vital to advancing technology, such as in the fields of electronics and data storage. Particularly in magnetic multilayers, the type and strength of interlayer coupling is essential to understanding unique material properties and effects. By engineering layers at the atomic level, scientists can tailor material properties like magnetic anisotropy, which is the directional dependence of a material's magnetic behaviour. Recent studies have explored the behaviour of magnetic oxides layered with metallic non-magnetic spacer layers, and this study aimed to build on that work.
Schöpf’s study explored the interactions between ferromagnetic La0.7Sr0.3 Mn0.95Ru0.05O3 (LSMRO) layers exhibiting perpendicular magnetic anisotropy (PMA), with paramagnetic metallic LaNiO3 (LNO) spacer layers. By varying the thickness of the LNO layers, the group were able to tailor the interlayer coupling from ferromagnetic (FM, magnetic moments align in same direction to reinforce magnetic field) to antiferromagnetic (neighbouring magnetic moments align in opposite directions, creating a zero magnetic field). Controlling the coupling type between layers of a multilayer structure holds promises for advancing the fields of spintronics and ultrahigh density memory devices.
The Challenge
Over five years of conducting the research project, the team struggled to find a constant and high-quality supply of LSAT substrates. The LSAT substrates form a lattice template for the epitaxial growth of the single-crystal layers. Given its complex composition, obtaining LSAT crystals with correct stoichiometry was crucial, however the team found that many crystal growers had difficulties growing these crystals successfully. Substrate quality, such as the polished surface quality, are vital for achieving coherent epitaxy, therefore poor-quality crystals had detrimental impacts on the research progress.
Single crystal substrates can also be used to tailor properties of the epitaxially-grown material via strain engineering. In particular, the LSAT substrate was used to introduce moderate compressive strain and consequently created perpendicular magnetic anisotropies (PMA) in the LSMRO layers; PMA was a crucial feature of materials studied in previous research. Overall, this results in the magnetic moments of the LSMRO aligning perpendicular to the plane of the material.
Furthermore, specialized sizes of LSAT substrates (4 mm x 4 mm) were required to perform SQUID magnetometry with perpendicular-to-surface magnetic field orientations. Superconducting Quantum Interference Device(SQUID) magnetometry is an extremely sensitive technique that can be used to measure various magnetic properties of a material, for example, the size and direction of a magnetic field. For this research, SQUID magnetometry was used to investigate the magnetic coupling of the epitaxial layers.
Overall, receiving high-quality and specialised LSAT substrates was vital for allowing the researchers to grow their thin films, for inducing specific desired magnetic properties, and for enabling analysis of the fabricated samples.
PI-KEM's Contribution
With over two decades of experience supplying advanced materials, our team has expert knowledge of the product quality and consistency needed for performing high-level techniques such as epitaxial crystal growth.
In December 2023, our Photonics and Optoelectronics Business Development Manager, Tom Pickford, visited the University of Cologne and was introduced to Dr Ionela Lindfors-Vrejoiu. Dr. Lindfors-Vrejoiu shared the challenges her team was facing in sourcing reliable, high-quality LSAT substrates, and Tom identified this as an excellent opportunity to provide tailored support and create solutions to the group’s specific requirements. Understanding the critical importance of substrate quality for successful epitaxial growth, Tom drew on PI-KEM’s extensive supplier network and in-house expertise to offer an effective solution to their challenges.
Our excellent supplier relationship allowed us to consistently supply high-quality substrates, that had the surface characteristics necessary for successful epitaxy, and were custom sized to meet the specific requirement for SQUID magnetometry. Our supply chain experience also enabled us to meet project time constraints and ensure experimental reproducibility. Customs and duty queries were answered promptly, and are now a routine experience. In general, the ordering process always went smoothly for them, and the substrates were consistently delivered earlier than initial estimates.
This thorough understanding of both the scientific goals and material demands laid the foundation for a successful and ongoing collaboration, helping to streamline the research process and reduce delays caused by inconsistent materials.
The Substrate Use
The fabrication of the samples began with a 4mm x 4mm LSAT (100) substrate, which was annealed at 1000°C in air for 2 hours. Subsequently, pulsed-laser deposition was used to deposit the layers of LSMRO and LNO, with the assistance of reflection high-energy electron diffraction (RHEED) to control the thickness of the film layers. The samples were grown in two formats: tri-layered with two LSMRO layers (8nm thick each) separated by LNO spacers of either 4- or 6-unitcells; or five layers of LSMRO separated by 4-unit cell LNO spacers.
Subsequently, techniques including magneto-optical Kerr effect (MOKE), anomalous Hall effect investigations, and SQUID magnetometry were used to analyse the fabricated samples. Analysis showed that the LNO acted as a suitable spacer to tune the interlayer coupling by changing the spacer thickness. Predictions were substantiated that in the trilayer sample, 4-unit cell LNO spacers would result in antiferromagnetic coupling, whereas 6-unit cell spacers would result in ferromagnetic coupling. For the samples with 5 LSMRO layers, the 4-unit cell LNO spacers also caused AFM, however the effective magnetic anisotropy changed, causing the magnetisation to be shifted closer to the plane of the sample. Furthermore, the 4-unit cell LNO spacers in the multilayer sample exhibited magnetic ordering, coupled to the magnetisation of the LSMRO layers.
This study showed demonstrable control over interlayer couple in manganite samples, and achieved strong antiferromagnetic coupling; this holds relevance for spintronics applications, such as in spin-value devices. Future work aims to explore the dependence on layer thickness and number of LSMRO layers, as well as further studying synthetic anti-ferromagnetic skyrmion bubbles in ferromagnetic oxide multilayers.
Results and Benefits
Since 2024, PI-KEM has provided several shipments of 4 mm × 4 mm LSAT substrates, each meeting the strict surface quality requirements needed for epitaxial growth. The research team noted that the substrates were “clean, smooth, and particle-free” after performing atomic force microscopy - ideal conditions for PLD growth.
“The quality was very good and reproducible, all crystals could be used for successful epitaxy”.
Orders were consistently delivered ahead of schedule, and the ordering process was smooth and responsive throughout, swiftly dealing with queries such as customs fees.
Furthermore, the customer continues to rely on PI-KEM to supply reliable advanced materials. Since publishing research involving the LSAT substrates, they have ordered scandate substrates, DyScO3, for the growth of ferroelectric layers, such as PbTiO3. The delivery was fast, and the quality was “very good”, with atomic force microscopy showing the surface topography to be valuable for epitaxy.
Overall, PI-KEM’s support was instrumental in helping the customer overcome a long-standing challenge in sourcing high-quality LSAT substrates for their ferromagnetic oxide research. By consistently supplying crystals with excellent surface morphology and structural integrity, PI-KEM enabled the team to carry out reliable and reproducible epitaxial growth. The availability of custom sizes, such as 4 mm × 4 mm substrates suitable for SQUID magnetometry, was another key advantage. Fast, smooth ordering processes and timely deliveries meant that the customer could maintain momentum in their research without delays. In short, PI-KEM not only supplied specialist materials but also provided the consistency and service reliability that helped the research progress efficiently and with confidence.
Moving Forwards
If you're facing challenges sourcing custom materials for demanding applications like epitaxial growth or magnetic measurements, PI-KEM can make a real difference. From consistent crystal quality and exacting specifications, to custom sizing and dependable delivery, we understand the details that matter to your research.
With decades of experience and a team that understands the technical demands of cutting-edge science, we’re committed to supporting your success. Get in touch with us today to see how we can support your next project or browse our specialist materials at www.pi-kem.co.uk
