<i>In situ</i>magnetometry studies of magnetoelectric LSMO/PZT heterostructures

Abstract

In order to identify and quantify characteristics of the magnetoelectric coupling at ferromagnetic/ferroelectric interfaces, epitaxial La${}_{1\ensuremath{-}x}$Sr${}_{x}$MnO${}_{3}$/Pb(Zr,Ti)O${}_{3}$ (LSMO/PZT) heterostructures were deposited by large-distance magnetron sputtering. The remarkably high lateral uniformity achieved in such films allowed for a ferroelectric device area of more than 6 mm${}^{2}$. This has enabled for superconductive quantum interference device (SQUID) measurements of the magnetic response to the systematically, completely in situ, varied remanent ferroelectric polarization. Temperature dependence of the magnetic modulation upon charging and the magnetic response to the ferroelectric stimulation indicate a field-effect dominated coupling mechanism and generally confirm the concept of electrostatic hole (${h}^{+}$) doping of LSMO. The modulation of magnetization was comprehensively analyzed for a broad range of electrostatically induced surface charge concentrations. For small charge modulations at low temperature a linear tuning coefficient of $\ensuremath{\approx}\ensuremath{-}3.6\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/{h}^{+}$ has been determined. This suggests the activation of an antiferromagnetic coupling, even for very small surface charge densities. Simultaneously, a shift in the magnetic transition temperature at higher surface charge concentration indicates the presence of a ferromagnetic phase at the LSMO/PZT interface. Eventually, a physical picture of magnetoelectric coupling is proposed in which these quantitative results are consistently interpreted, in terms of a surface-charge dependent electronic phase separation with the coexistence of antiferromagnetic and ferromagnetic regions at the ferromagnetic/ferroelectric interface.