Diamond anvil cell techniques, synchrotron-based infrared and Raman spectroscopies, and lattice dynamics calculations are combined with prior magnetic property work to reveal the pressure–temperature ...phase diagram of CoN(CN)22. The second-order structural boundaries converge on key areas of activity involving the spin state exposing how the pressure-induced local lattice distortions trigger the ferromagnetic → antiferromagnetic transition in this quantum material.
We investigated the series of temperature and field-driven transitions in LuFe2O4 by optical and Mössbauer spectroscopies, magnetization, and x-ray scattering in order to understand the interplay ...between charge, structure, and magnetism in this multiferroic material. We demonstrate that charge fluctuation has an onset well below the charge ordering transition, supporting the "order by fluctuation" mechanism for the development of charge order superstructure. Bragg splitting and large magneto-optical contrast suggest a low-temperature monoclinic distortion that can be driven by both temperature and magnetic field.
This work brings together diamond anvil cell techniques, vibrational spectroscopies, and complementary lattice dynamics calculations to investigate pressure-induced local lattice distortions in ...α-CoN(CN)22. Analysis of mode behavior and displacement patterns reveals a series of pressure-driven transitions that modify the CoN6 counter-rotations, distort the octahedra, and flatten the CNaxC linkages. These local lattice distortions may be responsible for the low temperature magnetic crossover. We also discuss prospects for negative thermal expansion and show that there is not a straightforward low pressure pathway between the pink α and blue β ambient pressure phases of CoN(CN)22.
We combined Raman and infrared vibrational spectroscopies with complementary lattice dynamics calculations and magnetization measurements to reveal the dynamic aspects of charge-lattice-spin coupling ...in CoN(CN)22. Our work uncovers electron-phonon coupling as a magnetic field-driven avoided crossing of the low-lying Co2+ electronic excitation with two ligand phonons and a magnetoelastic effect that signals a flexible local CoN6 environment. Their simultaneous presence indicates the ease with which energy is transferred over multiple length and time scales in this system.
We report the discovery of a magnetic quantum critical transition in MnN(CN)(2)(2) that drives the system from a canted antiferromagnetic state to the fully polarized state with amplified ...magnetoelastic coupling as an intrinsic part of the process. The local lattice distortions, revealed through systematic phonon frequency shifts, suggest a combined MnN(6) octahedra distortion+counterrotation mechanism that reduces antiferromagnetic interactions and acts to accommodate the field-induced state. These findings deepen our understanding of magnetoelastic coupling near a magnetic quantum critical point and away from the static limit.
We investigated magnetoelastic coupling through the field-driven transition to the fully polarized magnetic state in quasi-two-dimensional Cu(HF2)(pyz)2BF4 by magnetoinfrared spectroscopy. This ...transition modifies out-of-plane ring distortion and bending vibrational modes of the pyrazine ligand. The extent of these distortions increases with the field, systematically tracking the low-temperature magnetization. These distortions weaken the antiferromagnetic spin exchange, a finding that provides important insight into magnetic transitions in other copper halides.
We measured the low-lying crystal field levels of Nd3+ in Nd3Ga5SiO14 via magneto-optical spectroscopy and employed the extracted energies, magnetic moments, and symmetries to analyze the magnetic ...properties and test the spin liquid candidacy of this material. The exchange interaction is surprisingly small, a discovery that places severe constraints on models used to describe the ground state of this system. Further, it demonstrates the value of local-probe photophysical techniques for rare-earth-containing materials where bulk property measurements can be skewed by low-lying electronic structure.
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•RT photoconductivity (PC) model of response and decay in SnO2 film was proposed.•Surface BG electronic states are a source for excitation by photons with hv < Eg.•BG electron LDOS ...determines the magnitude and time of PC response.•Intergrain barrier height related to oxygen ionosorption determines PC decay time.•Structural disordering results in stretched exponential behavior of PC decay.
A phenomenological model of room temperature photoconductivity in nanocrystalline SnO2 under photon excitation below the fundamental bandgap based on electronic states located at the bottom part of the band gap was proposed. Nature of these states is related to the surface oxygen vacancies and Sn-derived electronic states. Appropriate distribution of these states was considered. Numerical simulation of the photoconductivity response and decay on the basis of balance rate equation for excited electrons and immobile holes was done. Analysis revealed that response time is determined by the photoionization cross section of these states and intensity of illumination. Stationary photoresponse is saturated due to the limited number of these states. Intergrain potential barrier that originated due to the ionosorbed oxygen is the main factor limiting the reverse annihilation process and determining the photoconductivity decay time. Stretched exponential behavior of the photoconductivity decay was interpreted in terms of structural and electronic film disordering that results in asymmetric probability distribution of intergrain barrier heights and corresponding distribution of time constants.
We investigated the optical properties of (NBu4)3Ni(NCS)5, a pentacoordinate Ni compound, and compared the results with the more traditional hexacoordinate analogue (NEt4)4Ni(NCS)6. On the basis of ...our complementary electronic structure calculations, the color properties of this high spin complex can be understood in terms of excitations between strongly hybridized orbitals with significant Ni d and ligand character. Variable temperature vibrational studies show mode softening with decreasing temperature and splitting near 200 K, trends that we attribute to improved low temperature intermolecular interactions and a weak structural phase transition, respectively.
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