Journal Article Fe3GeTe2 Néel-Bloch domain walls Research Support, Non-U.S. Gov't aberration-corrected scanning transmission electron microscopy antiferroelectric materials antiferroelectric thin films elastocaloric effect electrocaloric effect epitaxial ferroelectric ultrathin films ferroelectric bubbles first-principle-based effective Hamiltonian fourth order interactions freestanding heterostructures hysteresis loss membranes nanoscale bubble domains negative electrocaloric effect phase transition piezoresponse force microscopy ripples single-crystal complex oxides size effects skyrmions sodium niobate solid-state cooling spin invariants topological defects ultrathin ferroelectric films