In numerous systems, giant physical responses have been discovered when two phases coexist; for example, near a phase transition. An intermetallic FeRh system undergoes a first-order antiferromagnetic to ferromagnetic transition above room temperature and shows two-phase coexistence near the transition. Here we have investigated the effect of an electric field to FeRh/PMN-PT heterostructures and report 8% change in the electrical resistivity of FeRh films. Such a 'giant' electroresistance (GER) response is striking in metallic systems, in which external electric fields are screened, and thus only weakly influence the carrier concentrations and mobilities. We show that our FeRh films comprise coexisting ferromagnetic and antiferromagnetic phases with different resistivities and the origin of the GER effect is the strain-mediated change in their relative proportions. The observed behaviour is reminiscent of colossal magnetoresistance in perovskite manganites and illustrates the role of mixed-phase coexistence in achieving large changes in physical properties with low-energy external perturbation.

The critical size limit of voltage-switchable electric dipoles has extensive implications for energy-efficient electronics, underlying the importance of ferroelectric order stabilized at reduced dimensionality. We report on the thickness-dependent antiferroelectric-to-ferroelectric phase transition in zirconium dioxide (ZrO 2 ) thin films on silicon. The emergent ferroelectricity and hysteretic polarization switching in ultrathin ZrO 2 , conventionally a paraelectric material, notably persists down to a film thickness of 5 angstroms, the fluorite-structure unit-cell size. This approach to exploit three-dimensional centrosymmetric materials deposited down to the two-dimensional thickness limit, particularly within this model fluorite-structure system that possesses unconventional ferroelectric size effects, offers substantial promise for electronics, demonstrated by proof-of-principle atomic-scale nonvolatile ferroelectric memory on silicon. Additionally, it is also indicative of hidden electronic phenomena that are achievable across a wide class of simple binary materials.

Flexoelectricity refers to electric polarization generated by heterogeneous mechanical strains, namely strain gradients, in materials of arbitrary crystal symmetries. Despite more than 50 years of work on this effect, an accurate identification of its coupling strength remains an experimental challenge for most materials, which impedes its wide recognition. Here, we show the presence of flexoelectricity in the recently discovered polar vortices in PbTiO3/SrTiO3 superlattices based on a combination of machine-learning analysis of the atomic-scale electron microscopy imaging data and phenomenological phase-field modeling. By scrutinizing the influence of flexocoupling on the global vortex structure, we match theory and experiment using computer vision methodologies to determine the flexoelectric coefficients for PbTiO3 and SrTiO3. Our findings highlight the inherent, nontrivial role of flexoelectricity in the generation of emergent complex polarization morphologies and demonstrate a viable approach to delineating this effect, conducive to the deeper exploration of both topics.

A range of modern applications require large and tunable dielectric, piezoelectric or pyroelectric response of ferroelectrics. Such effects are intimately connected to the nature of polarization and how it responds to externally applied stimuli. Ferroelectric susceptibilities are, in general, strongly temperature dependent, diminishing rapidly as one transitions away from the ferroelectric phase transition (TC). In turn, researchers seek new routes to manipulate polarization to simultaneously enhance susceptibilities and broaden operational temperature ranges. Here, we demonstrate such a capability by creating composition and strain gradients in Ba1−xSrxTiO3 films which result in spatial polarization gradients as large as 35 μC cm−2 across a 150 nm thick film. These polarization gradients allow for large dielectric permittivity with low loss (ɛr≈775, tan δ<0.05), negligible temperature-dependence (13% deviation over 500 °C) and high-dielectric tunability (greater than 70% across a 300 °C range). The role of space charges in stabilizing polarization gradients is also discussed.

Magnetic anisotropy (MA) is one of the most important material properties for modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e., magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry. Extrinsic control over the MA is usually achieved by introducing shape anisotropy or exchange bias from another magnetically ordered material. Here we demonstrate a pathway to manipulate MA of 3d transition-metal oxides (TMOs) by digitally inserting nonmagnetic 5d TMOs with pronounced spin-orbit coupling (SOC). High-quality superlattices comprising ferromagnetic La 2/3 Sr 1/3 MnO 3 (LSMO) and paramagnetic SrIrO 3 (SIO) are synthesized with the precise control of thickness at the atomic scale. Magnetic easy-axis reorientation is observed by controlling the dimensionality of SIO, mediated through the emergence of a novel spin-orbit state within the nominally paramagnetic SIO.complex oxides | interfacial physics | magnetic anisotropy | emergent magnetism | strong spin-orbit coupling M agnetic anisotropy (MA) is one of the fundamental properties of magnetic materials. The widespread scientific interest in MA originates from its decisive role in determining a rich spectrum of physical responses, such as the Kondo effect (1), the magnetocaloric effect (2), magnetic skyrmions (3), etc. From a technological viewpoint, it is an important and promising approach to control MA by external stimuli, such as electric field (4). In general, there are two approaches to design MA of a ferromagnet. In the first approach one manipulates the intrinsic magnetocrystalline anisotropy (MCA), deriving from the local crystal symmetry and spin-orbit coupling (SOC) of the magnetic ion (5-7). Alternatively, one can tune the MA through extrinsic contributions to the anisotropy such as shape (8) or exchange coupling to a strong antiferromagnet (9).One focus of magnetism research is 3d transition-metal oxides (TMOs), a class of materials that exhibit various functionalities including ferromagnetism due to the strong electron-electron correlation. However, SOC is usually weak or negligible in 3d TMOs. On the other hand, the pronounced SOC of heavy elements has drawn attention in recent years due to the emergence of new topological states of matter (10-12) and spintronics (13,14). In contrast to 3d TMOs, the correlation strength is often too small in 5d TMOs to host magnetism. Therefore, it is an interesting approach to design systems that combine the merits of these two fundamental interactions. A similar ideal has been studied in metal multilayers (15, 16). However, it still remains an important challenge to explore the ideal in complex oxides, where a variety of emergent phenomena have been discovered due to the power of atomic-scale confinement and interfacial coupling (17-21).Here we present an approach toward accomplishing this goal by atomic-scale synthesis. By fabricating high-quality superlattices comprising 3d and 5d TMOs, we address two open questions: the effect of SOC on the functionality of 3d TMOs an...