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1.
Inorg Chem ; 56(9): 4950-4955, 2017 May 01.
Article in English | MEDLINE | ID: mdl-28414436

ABSTRACT

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 Co[N(CN)2]2. 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.

2.
Inorg Chem ; 52(24): 14148-54, 2013 Dec 16.
Article in English | MEDLINE | ID: mdl-24299233

ABSTRACT

This work brings together diamond anvil cell techniques, vibrational spectroscopies, and complementary lattice dynamics calculations to investigate pressure-induced local lattice distortions in α-Co[N(CN)2]2. 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 C-N(ax)-C 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 ß ambient pressure phases of Co[N(CN)2]2.

3.
Phys Rev Lett ; 111(4): 047202, 2013 Jul 26.
Article in English | MEDLINE | ID: mdl-23931402

ABSTRACT

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 Co[N(CN)2]2. 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.

4.
Phys Rev Lett ; 110(23): 237202, 2013 Jun 07.
Article in English | MEDLINE | ID: mdl-25167527

ABSTRACT

We report the discovery of a magnetic quantum critical transition in Mn[N(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.

5.
Phys Rev Lett ; 103(15): 157401, 2009 Oct 09.
Article in English | MEDLINE | ID: mdl-19905665

ABSTRACT

We investigated magnetoelastic coupling through the field-driven transition to the fully polarized magnetic state in quasi-two-dimensional [Cu(HF2)(pyz)2]BF4 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.

6.
Inorg Chem ; 48(16): 7650-8, 2009 Aug 17.
Article in English | MEDLINE | ID: mdl-19591482

ABSTRACT

We investigated the optical properties of (NBu(4))(3)[Ni(NCS)(5)], a pentacoordinate Ni compound, and compared the results with the more traditional hexacoordinate analogue (NEt(4))(4)[Ni(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.

7.
Phys Rev Lett ; 103(26): 267402, 2009 Dec 31.
Article in English | MEDLINE | ID: mdl-20366345

ABSTRACT

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.

8.
Phys Rev Lett ; 101(22): 227602, 2008 Nov 28.
Article in English | MEDLINE | ID: mdl-19113523

ABSTRACT

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.

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