TY - JOUR
T1 - Linking NH4+ motion to magnetism in molecular multiferroic (NH4)2[FeCl5(H2 O)]
T2 - A neutron vibrational spectroscopy study
AU - Tian, W.
AU - Daemen, L. L.
AU - Cheng, Y. Q.
AU - Li, Fei
AU - Fernandez-Baca, Jaime A.
N1 - Publisher Copyright:
© 2024 American Physical Society.
PY - 2024/8/1
Y1 - 2024/8/1
N2 - We present a neutron vibrational spectroscopy study to investigate the influence of NH4+ motion on the magnetism in [(NH4)1-xKx]2[FeCl5(H2O)]. The parent compounds, (NH4)2[FeCl5(H2O)] (x=0) and K2[FeCl5(H2O)](x=1) are isostructural at room temperature, yet displaying drastically different magnetic and multiferroic behavior. K2[FeCl5(H2O)] is nonmultiferroic with type-A collinear antiferromagnetic structure below TN≈14.06K, whereas (NH4)2[FeCl5(H2O)] is a type-II multiferroic with incommensurate cycloidal spin structure below TFE≈6.8K. A recent study of the dielectric, structure, and magnetic properties in the mixed [(NH4)1-xKx]2[FeCl5(H2O)] shows that a small amount of potassium substitution to replace NH4+ transforms the spin structure from incommensurate cycloidal (x≤ 0.06) into commensurate collinear antiferromagnetic (x≥ 0.15), indicating NH4+ is essential to the emergent phenomena observed in this molecular multiferroic compound. Our vibrational spectroscopy study reveals that NH4+ libration and torsion motion exhibit substantial temperature dependence at low temperatures. The intensity of NH4+ libration and torsion modes increases slightly at 5 K in comparison with data at 25 K behaving like a magnon, indicating that they are coupled to the magnetism in (NH4)2[FeCl5(H2O)]. Comparing data of x=0, 0.06, 0.09, and 0.15 samples further illustrates that the strength of the increased signal in NH4+ libration mode is very sensitive to potassium concentration. The signal diminishes quickly with increasing potassium concentration and vanishes in the x=0.15 sample corresponding to the magnetic structure change for x≥ 0.15. The results directly link the anomalous behavior in NH4+ libration motion to the magnetism in [(NH4)1-xKx]2[FeCl5(H2O)], providing new insights into the crucial role NH4+ plays in the coupled phenomena in (NH4)2[FeCl5(H2O)]. The unique information opens a new door to go through in searching for new multifunctional materials by incorporation of NH4 via a material-by-design approach.
AB - We present a neutron vibrational spectroscopy study to investigate the influence of NH4+ motion on the magnetism in [(NH4)1-xKx]2[FeCl5(H2O)]. The parent compounds, (NH4)2[FeCl5(H2O)] (x=0) and K2[FeCl5(H2O)](x=1) are isostructural at room temperature, yet displaying drastically different magnetic and multiferroic behavior. K2[FeCl5(H2O)] is nonmultiferroic with type-A collinear antiferromagnetic structure below TN≈14.06K, whereas (NH4)2[FeCl5(H2O)] is a type-II multiferroic with incommensurate cycloidal spin structure below TFE≈6.8K. A recent study of the dielectric, structure, and magnetic properties in the mixed [(NH4)1-xKx]2[FeCl5(H2O)] shows that a small amount of potassium substitution to replace NH4+ transforms the spin structure from incommensurate cycloidal (x≤ 0.06) into commensurate collinear antiferromagnetic (x≥ 0.15), indicating NH4+ is essential to the emergent phenomena observed in this molecular multiferroic compound. Our vibrational spectroscopy study reveals that NH4+ libration and torsion motion exhibit substantial temperature dependence at low temperatures. The intensity of NH4+ libration and torsion modes increases slightly at 5 K in comparison with data at 25 K behaving like a magnon, indicating that they are coupled to the magnetism in (NH4)2[FeCl5(H2O)]. Comparing data of x=0, 0.06, 0.09, and 0.15 samples further illustrates that the strength of the increased signal in NH4+ libration mode is very sensitive to potassium concentration. The signal diminishes quickly with increasing potassium concentration and vanishes in the x=0.15 sample corresponding to the magnetic structure change for x≥ 0.15. The results directly link the anomalous behavior in NH4+ libration motion to the magnetism in [(NH4)1-xKx]2[FeCl5(H2O)], providing new insights into the crucial role NH4+ plays in the coupled phenomena in (NH4)2[FeCl5(H2O)]. The unique information opens a new door to go through in searching for new multifunctional materials by incorporation of NH4 via a material-by-design approach.
UR - http://www.scopus.com/inward/record.url?scp=85201082974&partnerID=8YFLogxK
U2 - 10.1103/PhysRevB.110.064410
DO - 10.1103/PhysRevB.110.064410
M3 - Article
AN - SCOPUS:85201082974
SN - 2469-9950
VL - 110
JO - Physical Review B
JF - Physical Review B
IS - 6
M1 - 064410
ER -