Oak Ridge researchers used pressure to manipulate magnetism in thin film materials used to enhance performance in electronic devices. They used neutron scattering at Oak Ridge National Laboratory’s Spallation Neutron Source to explore the spacial density of atoms and observe how magnetism in a lanthanum-cobalt-oxide film changed with applied pressure.
Above – Researchers developed a one-of-a-kind, high-pressure cell and used it on the Magnetism Reflectometer beamline at ORNL’s Spallation Neutron Source to study the spatially confined magnetism in a lanthanum-cobalt-oxide thin film. Credit: Genevieve Martin/Oak Ridge National Laboratory, U.S. Dept. of Energy
“We developed a novel method to identify the critical role that strain has on the magnetism of films and their interfaces,” said ORNL’s Michael R. Fitzsimmons. “This allows us to study magnetism in thin films without having to compare a lot of differently grown samples.”
In the bulk, LaCoO3 (LCO) is a paramagnet, yet the low-temperature ferromagnetism (FM) is observed in tensile strained thin films, and its origin remains unresolved. They quantitatively measured the distribution of atomic density and magnetization in LCO films by polarized neutron reflectometry (PNR) and found that the LCO layers near the heterointerfaces exhibit a reduced magnetization but an enhanced atomic density, whereas the film’s interior (i.e., its film bulk) shows the opposite trend. We attribute the nonuniformity to the symmetry mismatch at the interface, which induces a structural distortion related to the ferroelasticity of LCO. This assertion is tested by systematic application of hydrostatic pressure during the PNR experiments. The magnetization can be controlled at a rate of −20.4% per GPa. These results provide unique insights into mechanisms driving FM in strained LCO films while offering a tantalizing observation that tunable deformation of the CoO6 octahedra in combination with the ferroelastic order parameter.
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