Induced Magnetization in ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3/{\mathrm{BiFeO}}_3$ Superlattices

Using polarized neutron reflectometry, we observe an induced magnetization of $75\pm 25\mathrm{kA}/\mathrm{m}$ at 10 K in a ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ $(\mathrm{LSMO})/{\mathrm{BiFeO}}_3$ superlattice extending from the interface through several atomic layers of the ${\mathrm{BiFeO}}_3$ (BFO). The induced magnetization in BFO is explained by density functional theory, where the size of band gap of BFO plays an important role. Considering a classical exchange field between the LSMO and BFO layers, we further show that magnetization is expected to extend throughout the BFO, which provides a theoretical explanation for the results of the neutron scattering experiment.

Figure 1

Polarized neutron reflectivity for a superlattice $[(\mathrm{LSMO}{)}_6/(\mathrm{BFO}{)}_5{]}_8$ on (100) ${\mathrm{SrTiO}}_3$ substrate. Measured data at 300 K (a) and at 10 K (b), as well as the fitting of data at 10 K with zero magnetization (c), antiferromagnetic (d), and ferromagnetic (e) models. For the field cooled measurement, the sample was initially cooled in a field of 1 kOe from 300 K, and then measured while warming the sample at the same field. Closed and open circles are experimental data for neutron with spin parallel ($R^{+}$) and antiparallel ($R^{-}$) to the magnetic field. Both solid black and solid green lines are the best fit to the experimental data.

Figure 2

The depth profile of the characteristic parameters for a superlattice $[(\mathrm{LSMO}{)}_6/(\mathrm{BFO}{)}_5{]}_8$ on (001) ${\mathrm{SrTiO}}_3$ substrate. (a) The nuclear scattering length density; and (b) The magnetization at 300 and 10 K, which gave the best fit to PNR data shown in Fig. 1. The dashed vertical line in (a) is used to distinguish the two interfaces of LSMO on BFO and BFO on LSMO.

Figure 3

Induced ferromagnetism on Fe sites for a $(\mathrm{LSMO}{)}_6/(\mathrm{BFO}{)}_5$ system obtained from the ab initio calculations with the value of Hubbard repulsion $U=4\mathrm{eV}$ (red lines) and $U=2\mathrm{eV}$ (blue lines). The layer index 1 denotes the Fe layer interfaced with LSMO through Bi atomic layer (with the interface symbolized by $\mathrm{Mn}/\mathrm{Bi}/\mathrm{Fe}$) while the layer index 5 denotes the Fe layer interfaced with LSMO through La(Sr) atomic layer [with the interface symbolized by $\mathrm{Fe}/\mathrm{La}(\mathrm{Sr})/\mathrm{Mn}$]. The inset shows the density of states for a bulk BFO with corresponding values of $U$.

Figure 4

Field effect on BFO produced by LSMO. (a) The idealized spin configuration for the LSMO/BFO heterostructure; (b) the canted spin configuration produced by the interaction exchange field for BFO, where the general loss of magnetization in LSMO is illustrated by a change in the net moment. It should be noted that the loss magnetization could also be due to a canting of the spins in LSMO; and (c) the simulated absolute magnetization (solid-blue line) and turn angle (dashed-red line) as a function of unit cell through the LSMO/BFO heterostructure. Here, the net magnetization is assumed to be measured parallel to the interface. The gray areas show the estimated region of the interlayer mixing, which is in the range of $\sim 2\mathrm{u}\mathrm{.}\mathrm{c}\mathrm{.}$