Combining ultrafast optical and x-ray spectroscopies for the study of emergent ferromagnetism at the LaNiO₃/CaMnO₃ interface

Epitaxial superlattices consisting of antiferromagnetic CaMnO₃ and paramagnetic LaNiO₃ exhibit emergent ferromagnetism that can be tuned by varying the thickness of individual layers. The thickness dependence of the interfacial magnetic moment can be attributed to the changes in the LaNiO₃ layer, which undergoes a metal-insulator transition in the ultrathin (few-unit-cell) limit. Here, we use a combination of resonant soft x-ray reflectivity and time-resolved magneto-optic Kerr effect, optical reflectivity, and transmissivity spectroscopies of variable-thickness LaNiO₃/CaMnO₃ superlattices to disentangle multiple interrelated electronic and magnetic processes driven by ultrafast high-field THz electric-field pulses. Our new understanding of these phenomena makes the LaNiO₃/CaMnO₃ system a prime candidate for high-density spintronic devices wherein energy-efficient magnetic switching could be accomplished with electric fields or other external stimuli.

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