Strain Control of Magnetism in LaCoO3

Coupling of ferroelastic and ferromagnetic order parameters in materials offers a means to achieve novel multiferroic applications. In this talk, we report strong coupling between the structural degree of freedom and spin state transition in the LaCoO₃ (LCO) thin films and heterostructures. Three major results will be present, 1) symmetry transition from a pesedocubic to a monoclinic structure happens in the LCO films as increasing the layer thickness, leading to the nonlinear behavior of magnetization vs. thickness; [1] 2) the observation of one-dimensional ferroelastic domains in LCO thin films that are intimately linked to magnetization. Unidirectional structural modulation is achieved by selective choice of substrate or growth plane, which produces broken in-plane rotational symmetry; [2] 3) the interfacial symmetry mismatch triggers the nonuniformed crystallographic parameters, thus the structural modification within a single LCO layer. The magnetization exhibits a reduced magnetization but an enhanced atomic density, whereas the film’s interior (i.e., its film bulk) shows the opposite trend. This assertion is tested by systematic application of hydrostatic pressure during the polarized neutron reflectivity experiments. The magnetization can be controlled at a rate of −20.4% per GPa. [3] 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 and ferromagnetic order parameters.
References
[1]. E. J. Guo, et al. Phys. Rev. Mater. 3, 014407 (2019).
[2]. E. J. Guo, et al., Science Advances 5, eaav5050 (2019).
[3]. E. J. Guo, et al., Phys. Rev. Lett. 122, 187202 (2019).