High-Field Magnetoelectric and Spin-Phonon Coupling in Multiferroic (NH4)2[FeCl5·(H2O)]

Hughey, Kendall D.; Lee, Minseong; Nam, Jisoo; Clune, Amanda J.; O’Neal, Kenneth R.; Tian, Wei; Fishman, Randy S.; Ozerov, Mykhaylo; Lee, JunHee; Zapf, Vivien S.; Musfeldt, Janice L.

doi:10.1021/acs.inorgchem.1c03311

Title: High-Field Magnetoelectric and Spin-Phonon Coupling in Multiferroic (NH₄)₂[FeCl₅·(H₂O)]

Journal Article · Wed Feb 16 00:00:00 EST 2022 · Inorganic Chemistry

DOI:https://doi.org/10.1021/acs.inorgchem.1c03311· OSTI ID:1847496

^[1]; Lee, Minseong ^[2]; Nam, Jisoo ^[3];

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Univ. of Tennessee, Knoxville, TN (United States)
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Ulsan National Inst. of Science and Technology (Korea)
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Florida State Univ., Tallahassee, FL (United States)

We combine high field polarization, magneto-infrared spectroscopy, and lattice dynamics calculations with prior magnetization to explore the properties of (NH₄)₂[FeCl₅·(H₂O)]-a type II molecular multiferroic in which the mixing between charge, structure, and magnetism is controlled by intermolecular hydrogen and halogen bonds. Electric polarization is sensitive to the series of field-induced spin reorientations, increasing linearly with the field and reaching a maximum before collapsing to zero across the quasi-collinear to collinear-sinusoidal reorientation due to the restoration of inversion symmetry. Magnetoelectric coupling is on the order of 1.2 ps/m for the P∥c, H∥c configuration between 5 and 25 T at 1.5 K. In this range, the coupling takes place via an orbital hybridization mechanism. Other forms of mixing are active in (NH₄)₂[FeCl₅·(H₂O)] as well. Magneto-infrared spectroscopy reveals that all of the vibrational modes below 600 cm^–1 are sensitive to the field-induced transition to the fully saturated magnetic state at 30 T. We analyze these local lattice distortions and use frequency shifts to extract spin-phonon coupling constants for the Fe–O stretch, Fe–OH₂ rock, and NH₄⁺ libration. Inspection also reveals subtle symmetry breaking of the ammonium counterions across the ferroelectric transition. Here, the coexistence of such varied mixing processes in a platform with intermolecular hydrogen- and halogen-bonding opens the door to greater understanding of multiferroics and magnetoelectrics governed by through-space interactions.

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Research Organization:: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES)

Grant/Contract Number:: AC05-00OR22725

OSTI ID:: 1847496

Journal Information:: Inorganic Chemistry, Vol. 61, Issue 8; ISSN 0020-1669

Publisher:: American Chemical Society (ACS)Copyright Statement

Country of Publication:: United States

Language:: English

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Magnetic properties
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Title: High-Field Magnetoelectric and Spin-Phonon Coupling in Multiferroic (NH4)2[FeCl5·(H2O)]

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Title: High-Field Magnetoelectric and Spin-Phonon Coupling in Multiferroic (NH₄)₂[FeCl₅·(H₂O)]