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A large electrocaloric effect is reported in a strain-engineered Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) thin film heterostructure driven by the near room-temperature electro-structural phase transition. An epitaxial BCZT/La0.7Sr0.3MnO3 (BCZT/LSMO) heterostructure was grown on a single-crystal SrTiO3 (100) substrate using pulsed laser deposition. In-depth x-ray diffraction and x-ray spectroscopic analyses revealed the single-crystalline nature and stoichiometric growth of the heterostructure. Both temperature dependent x-ray diffraction and dielectric measurements revealed a broad second-order-type phase transition near 430 K in the BCZT/LSMO heterostructure. From detailed theoretical analyses of the experimental data, it was confirmed that the phase transition around 430 K is second-order in nature, unlike the first-order transition observed in bulk BCZT materials. Thermodynamic analyses of polarization revealed an unprecedently large adiabatic temperature change of 13.5 K at 430 K under a field change of 1000 kV cm−1, hitherto unobserved in a lead-free material. Extremely broad adiabatic temperature change ΔT(T) curves over a wide working range of temperatures (330 K < T < 480 K) resulted in enhanced relative cooling powers, which are higher than those reported so far in most electrocaloric materials. We propose that an interfacial strain-induced enhanced tetragonal distortion of the BCZT layer gives rise to these large electrocaloric effects in the BCZT/LSMO heterostructure system. The demonstration of a large electrocaloric effect in the lead-free BCZT thin film may open up new pathways toward the design of artificial heterostructures for eco-friendly solid-state cooling applications.

Using ferromagnetic La0.67Sr0.33MnO3 electrodes bridged by single-layer graphene, we observe magnetoresistive changes of ∼32–35 MΩ at 5 K. Magneto-optical Kerr effect microscopy at the same temperature reveals that the magnetoresistance arises from in-plane reorientations of electrode magnetization, evidencing tunnelling anisotropic magnetoresistance at the La0.67Sr0.33MnO3-graphene interfaces. Large resistance switching without spin transport through the non-magnetic channel could be attractive for graphene-based magnetic-sensing applications.

We used finite element analysis to model the flow of heat in multilayer capacitors (MLCs) that comprise good electrocaloric materials and high-thermal-conductivity electrodes. An ideal heat pump based on these MLCs could develop a sustained cooling power of 81.7 kW m−2. This supersedes the 36 kW m−2 predicted by a lumped thermal model [S. Kar-Narayan and N. D. Mathur, Appl. Phys. Lett. 95, 242903 (2009)]. We show that geometrical optimization increases predicted cooling power to 215 kW m−2.

We present two techniques for directly measuring electrocaloric temperature change in a multilayer capacitor based on BaTiO3. Scanning thermal microscopy with resolution 80 mK, and infra-red imaging with resolution 25 mK, each record electrocaloric temperature changes of ∼0.5 K that match within error. We find that scanning thermal microscopy is more suitable for detecting giant electrocaloric effects in thin films with substrates present.

We argue that the multilayer capacitor (MLC) geometry is ideal for electrocaloric cooling. Thermal modeling predicts that a commercially available MLC, which serendipitously shows electrocaloric effects, could constitute the heart of an idealized heat pump delivering a continuous cooling power of 22.5 W kg−1. This figure could be increased via materials optimization to ∼2875 W kg−1, such that an MLC array whose sheet area is just ∼0.56 m2 would deliver the ∼20 kW cooling power of typical air-cooled chillers for air-conditioning at residential and commercial sites. Expensive materials are not required, and performance could be further enhanced via geometrical improvements.

We report electrically induced changes of 20% in both the remnant magnetization and the coercive field of a magnetoelectric heterostructure. This heterostructure is an industrially produced multilayer capacitor comprising Ni-based magnetostrictive electrodes sandwiching a BaTiO3-based dielectric that is ferroelectric and therefore piezoelectric. Both magnetization and strain are shown to be hysteretic with applied electric field. These inexpensive capacitors might find use as electrically controlled ferromagnets.