AsianScientist (Aug. 19, 2015) – Researchers have shown that when the antiferromagnetic oxide of lanthanum and manganese (LaMnO3) is grown in six or more layers, it abruptly becomes magnetic. These results, published in Science, highlight the possibility of controlling the magnetic and electronic properties of nanostrcutured materials.
Magnetism in nanoscale layers only a few tens of atoms thick is one of the foundations of the big data revolution. For example, all the information we download from the internet is stored magnetically on hard disks in server farms dotted across the world.
Using pulsed laser deposition, a team of researchers from the National University of Singapore (NUS) led by Professor T. Venky Venkatesan first grew perfectly crystalline atomic layers of LaMnO3 on a substrate crystal of non-magnetic strontium titanate (SrTiO3). This method was first developed by many years ago for high-temperature superconductors and multicomponent materials by Venkatesan, who now heads the NUS Nanoscience and Nanotechnology Institute (NUSNNI).
At the atomically thin scale, LaMnO3 is an antiferromagnet and shows no magnetism. However, the researchers found that when grown to six or more layers, LaMnO3 abruptly becomes uniformly magnetic, as visualized by a magnetic microscopy technique called scanning superconducting quantum interference device (SQUID) microscopy.
The researchers propose is that this abrupt magnetism arises from an avalanche of electrons from the top surface of the film to the bottom, where the electrons are confined near the substrate. This shift of electric charge occurs as the manganese atomic layers form atomically charged capacitors leading to the build-up of an electric field—known as ‘polar catastrophe’—inside the LaMnO3.
The work validates the polar catastrophe model, and demonstrates how the addition of just one extra atomic layer can transform the magnetism.
The team plans to use local electric fields to controllably turn on/off the magnetism of its five-layer films, and explore potential applications in microwave devices and magnetic recording. With magnetic memory elements approaching nano dimensions, this technique promises new approaches in magnetic recording and computing.
The article can be found at: Wang et al. (2015) Imaging and Control of Ferromagnetism in LaMnO₃/SrTiO₃ Heterostructures.
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Source: National University of Singapore.
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