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Abstract: Spinel oxides are well-known functional materials but rarely show superconductivity. Recently, emergent superconductivity was discovered in MgTi 2 O 4 , which is attributed to the increase of electron doping and the suppression of orbital order. Here, we utilized Ti L -edge resonant inelastic x-ray scattering to study the orbital excitations in superconducting (SC) and insulating MgTi 2 O 4 films. We find that the spectral weight of orbital excitations is enhanced and the energy of t 2 g intraband excitation is softened in the SC film compared to the insulating one, suggesting higher electron doping and a suppressed orbital order gap in the SC sample. These observations were further supported by our multiplet calculations using the minimal two-site model. Our results provide spectroscopic evidence for the competition between orbital order and superconductivity in MgTi 2 O 4 and shed light on searching for novel superconductors in spinel oxides.

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Abstract: For the first time, the origin of large electrostrain in pseudocubic BiFeO 3 -based ceramics is verified with direct structural evidence backed by appropriate simulations. We employ advanced structural and microstructural characterizations of BiFeO 3 -based ceramics that exhibit large electrostrain ( > 0.4 % ) to reveal the existence of multiple, nanoscale local symmetries, dominantly tetragonal or orthorhombic, which have a common, averaged direction of polarization over larger, meso- or microscale regions. Phase-field simulations confirm the existence of local nanoscale symmetries, thereby providing a new vision for designing high-performance lead-free ceramics for high-strain actuators.

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Abstract: The size of the orbital moment in Fe 3 O 4 has been the subject of a long-standing and contentious debate. In this paper, we make use of ferromagnetic resonance (FMR) spectroscopy and x-ray magnetic circular dichroism (XMCD) to provide complementary determinations of the size of the orbital moment in “bulklike” epitaxial Fe 3 O 4 films grown on yttria-stabilized zirconia (111) substrates. Annealing the 100 nm as-grown films to 1100 ∘ C in a reducing atmosphere improves the stoichiometry and microstructure of the films, allowing for bulklike properties to be recovered as evidenced by x-ray diffraction and vibrating sample magnetometry. In addition, in-plane angular FMR spectra exhibit a crossover from a fourfold symmetry to the expected sixfold symmetry of the (111) surface, together with an anomalous peak in the FMR linewidth at ∼ 10 GHz; this is indicative of low Gilbert damping in combination with two-magnon scattering. For the bulklike annealed sample, a spectroscopic splitting factor g ≈ 2.18 is obtained using both FMR and XMCD techniques, providing evidence for the presence of a finite orbital moment in Fe 3 O 4 .

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Abstract: High-resolution calorimetry has played a significant role in providing detailed information on phase transitions in liquid crystals. In particular, adiabatic scanning calorimetry (ASC), capable of providing simultaneous information on the temperature dependence of the specific enthalpy h ( T ) and on the specific heat capacity c p ( T ) , has proven to be an important tool to determine the order of transitions and render high-resolution information on pretransitional thermal behavior. Here we report on ASC results on the compound 2,3′,4′,5′-tetrafluoro[1,1′-biphenyl]-4-yl 2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) and on mixtures with 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). Both compounds exhibit a low-temperature ferroelectric nematic phase ( N F ) and a high-temperature paraelectric nematic phase ( N ) . However, in DIO these two phases are separated by an intermediate phase ( N x ). From the detailed data of h ( T ) and c p ( T ) , we found that the intermediate phase was present in all the mixtures over the complete composition range, albeit with strongly decreasing temperature width for that phase with decreasing mole fraction of DIO ( x DIO ). The x DIO dependence on the transition temperatures for both transitions could be well described by a quadratic function. Both these transitions were weakly first order. The true latent heat of the N x − N transition of DIO was as low as L = 0.0075 ± 0.0005 J / g and L = 0.23 ± 0.03 J / g for the N F − N x transition, which is about twice the previously reported value of 0.115 J/g for the N F − N transition in RM734. In the mixtures both transition latent heats decrease gradually with decreasing x DIO . At all the N x − N transitions pretransition fluctuation effects are absent and these transitions are purely but very weakly first order. As in RM734 the transition from the N F to the higher-temperature phase exhibits substantial pretransitional behavior, in particular, in the high-temperature phase. Power-law analysis of c p ( T ) resulted in an effective critical exponent α = 0.88 ± 0.1 for DIO and this value decreased in the mixtures with decreasing x DIO toward α = 0.50 ± 0.05 reported for RM734. Ideal mixture analysis of the phase diagram was consistent with ideal mixture behavior provided the total transition enthalpy change was used in the analysis.

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Abstract: The Bragg diffraction of neutrons and x rays are well suited to the task of determining the distribution of magnetization in crystals. Applications of the two techniques proceed by contrasting observed intensities with intensities calculated with a specific model, and changing the model as need be to achieve satisfactory agreement. An all-in–all-out (AIAO) magnetic configuration of magnetic dipoles on a cubic face-centered lattice with networks of corner-sharing tetrahedra is often mentioned in the context of pyrochlore oxides, for example, but the corresponding neutron and x-ray-diffraction patterns appear to not have been calculated. Our results for patterns of Bragg spots from an AIAO magnetic configuration defined by a magnetic space group are symmetry informed and yield exact reflection conditions. Specifically, a long-range order of magnetic dipoles is forbidden in our model. Bulk properties arise from higher-order multipoles that include quadrupoles and octupoles. Bragg spots that exclude all magnetic multipoles other than an octupole have been discovered, and they can be observed by both neutron diffraction and resonant x-ray diffraction. All magnetic multipoles allowed in diffraction by cerium ions ( 4 f 1 ) are presented in terms of coefficients in a well-documented and unusual magnetic ground state. Symmetry of the cerium site in the cubic structure constrains the coefficients. Our scattering amplitudes have an application in both neutron- and x-ray diffraction experiments on Ce 2 Zr 2 O 7 , for example, and searches for the sought-after cerium octupole. Also presented for future use is a result for the total, energy-integrated magnetic neutron-scattering intensity by a powder sample.