Abstract
We report a neutron diffraction study of the multiferroic mechanism in (ND4)2FeCl5·D2O, a molecular compound that exhibits magnetically induced ferroelectricity. This material exhibits two successive magnetic transitions on cooling: a long-range order transition to an incommensurate (IC) collinear sinusoidal spin state at TN=7.3 K, followed by a second transition to an IC cycloidal spin state at TFE=6.8 K, the latter of which is accompanied by spontaneous ferroelectric polarization. The cycloid structure is strongly distorted by spin-lattice coupling, as evidenced by the observations of both odd and even higher-order harmonics associated with the cycloid wave vector, and a weak commensurate phase that coexists with the IC phase. The second-order harmonic appears at TFE, thereby providing unambiguous evidence that the onset of the electric polarization is accompanied by a lattice modulation due to spin-lattice interaction. The neutron results, in conjunction with the negative thermal expansion and large magnetostriction observed in Ref. [19], indicate that spin-lattice coupling plays a critical role in the ferroelectric mechanism of (ND4)2FeCl5·D2O.
Original language | English |
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Article number | 214405 |
Journal | Physical Review B |
Volume | 94 |
Issue number | 21 |
DOIs | |
State | Published - Dec 7 2016 |
Funding
The research work at ORNL's High Flux Isotope Reactor and Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. J.Q.Y., B.C.S., and R.S.F. were supported by the Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.