Ferroelectric and ferromagnetic materials exhibit long-range order of atomic-scale electric or magnetic dipoles that can be switched by applying an appropriate electric or magnetic field, respectively. Both switching phenomena form the basis of non-volatile random access memory1, but in the ferroelectric case, this involves destructive electrical reading and in the magnetic case, a high writing energy is required2. In principle, low-power and high-density information storage that combines fast electrical writing and magnetic reading can be realized with magnetoelectric multiferroic materials3. These materials not only simultaneously display ferroelectricity and ferromagnetism, but also enable magnetic moments to be induced by an external electric field, or electric polarization by a magnetic field4,5. However, synthesizing bulk materials with both long-range orders at room temperature in a single crystalline structure is challenging because conventional ferroelectricity requires closed-shell d0 or s2 cations, whereas ferromagnetic order requires open-shell dn configurations with unpaired electrons6. These opposing requirements pose considerable difficulties for atomic-scale design strategies such as magnetic ion substitution into ferroelectrics7,8. One material that exhibits both ferroelectric and magnetic order is BiFeO3, but its cycloidal magnetic structure9 precludes bulk magnetization and linear magnetoelectric coupling10. A solid solution of a ferroelectric and a spin-glass perovskite combines switchable polarization11 with glassy magnetization, although it lacks long-range magnetic order12. Crystal engineering of a layered perovskite has recently resulted in room-temperature polar ferromagnets13, but the electrical polarization has not been switchable. Here we combine ferroelectricity and ferromagnetism at room temperature in a bulk perovskite oxide, by constructing a percolating network of magnetic ions with strong superexchange interactions within a structural scaffold exhibiting polar lattice symmetries at a morphotropic phase boundary14 (the compositional boundary between two polar phases with different polarization directions, exemplified by the PbZrO3–PbTiO3 system) that both enhances polarization switching and permits canting of the ordered magnetic moments. We expect this strategy to allow the generation of a range of tunable multiferroic materials.
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This work was supported by the EPSRC under EP/H000925/1. M.J.R. is a Royal Society Research Professor.
The authors declare no competing financial interests.
Extended data figures and tables
Left, magnetization versus temperature, cooled in zero applied field (ZFC, black line), cooled in 1 mT applied field (FC, red line) and the thermal remanent magnetization in zero applied field (TRM, blue line). Note negative TRM curve is due to a negative remanent magnetic field in the superconducting magnet. Right, magnetization versus magnetic field at 100 K.
Extended Data Figure 2 PXRD patterns obtained from six compositions of the series (1 − x)BiTi(1 − y)/2FeyMg(1 − y)/2O3–(x)CaTiO3 where x = 0.15, 0.60 ≤ y ≤ 0.90.
The weak reflection marked with the † symbol, which is visible in the y = 0.70 and y = 0.75 patterns, corresponds to the most intense reflection of sillenite (Bi25FeO40). All other peaks are indexed to the target perovskite phase using rhombohedral, rhombohedral + orthorhombic, or monoclinic cells, as discussed in the text.
Extended Data Figure 3 Pawley fits to PXRD patterns collected from two compositions of the series (1 − x)BiTi(1 − y)/2FeyMg(1 − y)/2O3–(x)CaTiO3.
a–f, x = 0.15, y = 0.60 (a–c) and x = 0.15, y = 0.80 (d–f) modelled as a single rhombohedral phase in space group R3c (a, d), as a combination of rhombohedral (R3c) and orthorhombic (Pna21) phases (b, e) and as a single monoclinic phase in space group P11a, which is a subgroup of R3c and Pna21 (c, f). Black circles, yobs; red line, ycalc; teal line, (yobs − ycalc); blue markers, hkl (R3c) reflections; green markers, hkl (Pna21) reflections; magenta markers, hkl (P11a) reflections. Insets are zooms of the main plots.
a, Frequency dependence of dielectric permittivity (left axis, dashed line) and loss (right axis, solid line) at 300 K for x = 0.15, y = 0.60 (black) and x = 0.15, y = 0.80 (red). b, A typical P(E) loop (right axis, blue line) with the corresponding current density (JPE; left axis, black line) and the leakage current density (JL; left axis, red line) for x = 0.15, y = 0.80. c, The polarization (blue line, left axis) and electric field profile (red dotted line, right axis) from PUND measurement of x = 0.15, y = 0.80 (see Methods for details). d, Temperature dependence of dc resistivity of x = 0.15, y = 0.80, showing highly insulating behaviour. In a–c, the arrows point to the relevant axis for each curve.
a, b, x = 0.15, y = 0.60 at T = 10 K < TN (a) and x = 0.15, y = 0.80 at T = 300 K < TN (b). The experimental data are represented as black filled circles. Red lines show the sum of the perovskite phase (blue line) and spinel impurity phase (green dashed line) contributions. c, x = 0.15, y = 0.60 at T = 300 K > TN and x = 0.15, y = 0.80 at T = 395 K > TN. The experimental data are represented as open circles (x = 0.15, y = 0.60) or squares (x = 0.15, y = 0.80); green dash-dotted and dashed lines show extracted spinel impurity contributions for x = 0.15, y = 0.60 and x = 0.15, y = 0.80, respectively; red lines show fits to the data.
a, b, Thermal remanent magnetization (TRM; left axis, black circles) and derivative of TRM with respect to temperature (dMTRM/dT; right axis, blue lines) for x = 0.15, y = 0.60 (a) and x = 0.15, y = 0.80 (b). Arrows indicate the axis that each dataset corresponds to.
Red squares are mean values, error bars in red are standard errors from 10 repeated measurements. The blue line is a linear fit to the data.
a, b, Measurements for x = 0.15, y = 0.60 at frequency f = 100 Hz (a) and x = 0.15, y = 0.80 at frequency f = 150 Hz (b) at 473 K.
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Mandal, P., Pitcher, M., Alaria, J. et al. Designing switchable polarization and magnetization at room temperature in an oxide. Nature 525, 363–366 (2015). https://doi.org/10.1038/nature14881
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