Single‐phase multiferroic materials are of considerable interest for future memory and sensing applications. Thin films of Aurivillius phase Bi ₇ Ti ₃ Fe ₃ O ₂₁ and Bi ₆ Ti _2.8 Fe _1.52 Mn _0.68 O ₁₈ (possessing six and five perovskite units per half‐cell, respectively) have been prepared by chemical solution deposition on c‐plane sapphire. Superconducting quantum interference device magnetometry reveal Bi ₇ Ti ₃ Fe ₃ O ₂₁ to be antiferromagnetic (T_N = 190 K) and weakly ferromagnetic below 35 K, however, Bi ₆ Ti _2.8 Fe _1.52 Mn _0.68 O ₁₈ gives a distinct room‐temperature in‐plane ferromagnetic signature (M_s = 0.74 emu/g, μ₀H_c =7 mT). Microstructural analysis, coupled with the use of a statistical analysis of the data, allows us to conclude that ferromagnetism does not originate from second phase inclusions, with a confidence level of 99.5%. Piezoresponse force microscopy (PFM) demonstrates room‐temperature ferroelectricity in both films, whereas PFM observations on Bi ₆ Ti _2.8 Fe _1.52 Mn _0.68 O ₁₈ show Aurivillius grains undergo ferroelectric domain polarization switching induced by an applied magnetic field. Here, we show for the first time that Bi ₆ Ti _2.8 Fe _1.52 Mn _0.68 O ₁₈ thin films are both ferroelectric and ferromagnetic and, demonstrate magnetic field‐induced switching of ferroelectric polarization in individual Aurivillius phase grains at room temperature.

Coupled ferromagnetic and ferroelectric materials, known as multiferroics, are an important class of materials that allow magnetism to be manipulated through the application of electric fields. Bismuth ferrite, BiFeO₃, is the most-studied intrinsic magnetoelectric multiferroic because it maintains both ferroelectric and magnetic ordering to well above room temperature. Here we report the use of epitaxy-free wet chemical methods to create strained nanoporous BiFeO₃. We find that the strained material shows large changes in saturation magnetization on application of an electric field, changing from 0.04 to 0.84 μ_b per Fe. For comparison, non-porous films produced using analogous methods change from just 0.002 to 0.01 μ_b per Fe on application of the same electric field. The results indicate that nanoscale architecture can complement strain-layer epitaxy as a tool to strain engineer magnetoelectric materials.