Tuning the Competition between Ferromagnetism and Antiferromagnetism in a Half-Doped Manganite through Magnetoelectric Coupling

We investigate the possibility of controlling the magnetic phase transition of the heterointerface between a half-doped manganite ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_3$ and a multiferroic ${\mathrm{BiFeO}}_3$ (BFO) through magnetoelectric coupling. Using macroscopic magnetometry and element-selective x-ray magnetic circular dichroism at the Mn and Fe $L$ edges, we discover that the ferroelectric polarization of BFO controls simultaneously the magnetization of BFO and ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_3$ (LCMO). X-ray absorption spectra at the oxygen $K$ edge and linear dichroism at the Mn $L$ edge suggest that the interfacial coupling is mainly derived from the superexchange between Mn and Fe $t_{2g}$ spins. The combination of x-ray absorption spectroscopy and mean-field theory calculations reveals that the $d$-electron modulation of Mn cations changes the magnetic coupling in LCMO, which controls the enhanced canted moments of interfacial BFO via the interfacial coupling. Our results demonstrate that the competition between ferromagnetic and antiferromagnetic instability can be modulated by an electric field at the heterointerface, providing another pathway for the electrical field control of magnetism.

Figure 1

Schematic of the heterostructures: (a) structure $H1$ for ferroelectric switch, (b) structure $H2$ for XAS, XMCD, and XLD; (c), (d) PFM of $H1$ structure in $P1$ and $P2$ states.

Figure 2

Temperature dependence of magnetization of $P1$ and $P2$ states taken with a magnetometer and calculated with the spin sum rule of XMCD.

Figure 3

(a), (c) The XAS and XMCD spectra of the Mn, Fe $L_{2,3}$ edge in $P1$ and $P2$ states; (b), (d) multiple repeats of XMCD of the Mn, Fe $L_{2,3}$ edge; (e) XAS of the oxygen $K$ edge with linear polarized x ray; (f) XLD spectra of the Mn $L_{2,3}$ edge [I(a) and I(c) correspond to XAS measured with in-plane and out-of-plane polarization, respectively]. XLD is measured at 300 K, where the magnetic dichroic effect is absent. All the data are taken from $H2$ (5 nm LCMO) except (b).

Figure 4

Mean-field theory calculations on the relationship between $e_g$ electron density ($N$) and spin structure for hole (a) and electron (b) doping of LCMO (${\theta }_2$ is the relative angle between neighboring spins across the zigzag chain); (c) schematic of the electron density and spin structure at the heterointerfaces (the dark-light contrast suggests the electron accumulation or depletion).