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  1. Hybrid molecular beam epitaxy (MBE) growth of Sn-modified BaTiO 3 films was realized with varying domain structures and crystal symmetries across the entire composition space. Macroscopic and microscopic structures and the crystal symmetry of these thin films were determined using a combination of optical second harmonic generation (SHG) polarimetry and scanning transmission electron microscopy (STEM). SHG polarimetry revealed a variation in the global crystal symmetry of the films from tetragonal ( P4 mm) to cubic [Formula: see text] across the composition range, x = 0 to 1 in BaTi 1− x Sn x O 3 (BTSO). STEM imaging shows that the long-range polar order observed when the Sn content is low ( x = 0.09) transformed to a short-range polar order as the Sn content increased ( x = 0.48). Consistent with atomic displacement measurements from STEM, the largest polarization was obtained at the lowest Sn content of x = 0.09 in Sn-modified BaTiO 3 as determined by SHG. These results agree with recent bulk ceramic reports and further identify this material system as a potential replacement for Pb-containing relaxor-based thin film devices.
    Free, publicly-accessible full text available March 1, 2024
  2. SrTiO 3 (STO) is an incipient ferroelectric perovskite oxide for which the onset of ferroelectric order is suppressed by quantum fluctuations. This property results in a very large increase in static dielectric constant from ∼300 at room temperature to ∼20,000 at liquid He temperature in bulk single crystals. However, the low-temperature dielectric constant of epitaxial STO films is typically a few hundred to a few thousand. Here, we use all-epitaxial capacitors of the form n -STO/undoped STO/ n -STO (001) prepared by hybrid molecular beam epitaxy, to demonstrate intrinsic dielectric constants of an unstrained STO (001) film exceeding 25,000. We show that the n -STO/undoped STO interface plays a critically important role not previously considered in determining the dielectric properties that must be properly accounted for to determine the intrinsic dielectric constant.
    Free, publicly-accessible full text available June 7, 2023
  3. Abstract

    We present a strategy for the design of ferromagnetic materials with exceptionally low magnetic hysteresis, quantified by coercivity. In this strategy, we use a micromagnetic algorithm that we have developed in previous research and which has been validated by its success in solving the “Permalloy Problem”—the well-known difficulty of predicting the composition 78.5% Ni of the lowest coercivity in the Fe–Ni system—and by the insight it provides into the “Coercivity Paradox” of W. F. Brown. Unexpectedly, the design strategy predicts that cubic materials with large saturation magnetizationmsand large magnetocrystalline anisotropy constantκ1will have low coercivity on the order of that of Permalloy, as long as the magnetostriction constantsλ100, λ111are tuned to special values. The explicit prediction for a cubic material with low coercivity is the dimensionless number$$({c}_{11}-{c}_{12}){\lambda }_{100}^{2}/(2{\kappa }_{1})=81$$(c11c12)λ1002/(2κ1)=81for 〈100〉 easy axes. The results would seem to have broad potential application, especially to magnetic materials of interest in energy research.