Radiative cooling is a passive cooling
technology that offers great
promises to reduce space cooling cost, combat the urban island effect,
and alleviate the global warming. To achieve passive daytime radiative
cooling, current state-of-the-art solutions often utilize complicated
multilayer structures or a reflective metal layer, limiting their
applications in many fields. Attempts have been made to achieve passive
daytime radiative cooling with single-layer paints, but they often
require a thick coating or show partial daytime cooling. In this work,
we experimentally demonstrate remarkable full-daytime subambient cooling
performance with both BaSO4 nanoparticle films and BaSO4 nanocomposite paints. BaSO4 has a high electron
band gap for low solar absorptance and phonon resonance at 9 μm
for high sky window emissivity. With an appropriate particle size
and a broad particle size distribution, the BaSO4 nanoparticle
film reaches an ultrahigh solar reflectance of 97.6% and a high sky
window emissivity of 0.96. During field tests, the BaSO4 film stays more than 4.5 °C below ambient temperature or achieves
an average cooling power of 117 W/m2. The BaSO4-acrylic paint is developed with a 60% volume concentration to enhance
the reliability in outdoor applications, achieving a solar reflectance
of 98.1% and a sky window emissivity of 0.95. Field tests indicate
similar cooling performance to the BaSO4 films. Overall,
our BaSO4-acrylic paint shows a standard figure of merit
of 0.77, which is among the highest of radiative cooling solutions
while providing great reliability, convenient paint form, ease of
use, and compatibility with the commercial paint fabrication process.
Low-loss magnetization dynamics and strong magnetoelastic coupling are generally mutually exclusive properties due to opposing dependencies on spin-orbit interactions. So far, the lack of low-damping, magnetostrictive ferrite films has hindered the development of power-efficient magnetoelectric and acoustic spintronic devices. Here, magnetically soft epitaxial spinel NiZnAl-ferrite thin films with an unusually low Gilbert damping parameter (<3 × 10 ), as well as strong magnetoelastic coupling evidenced by a giant strain-induced anisotropy field (≈1 T) and a sizable magnetostriction coefficient (≈10 ppm), are reported. This exceptional combination of low intrinsic damping and substantial magnetostriction arises from the cation chemistry of NiZnAl-ferrite. At the same time, the coherently strained film structure suppresses extrinsic damping, enables soft magnetic behavior, and generates large easy-plane magnetoelastic anisotropy. These findings provide a foundation for a new class of low-loss, magnetoelastic thin film materials that are promising for spin-mechanical devices.
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