Unconventional multiferroicity induced by structural distortion and magnetostriction effect in the layered spin-1/2 ferrimagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Bi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Cu</mml:mi><mml:mn>5</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">B</mml:mi><mml:mn>4</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>14</mml:mn></mml:msub></mml:mrow></mml:math>
Arkadeb Pal, T. W. Yen, T. W. Kuo, Chin‐Wei Wang, Shin-Ming Huang, M. C. Chou, Yen‐Chung Lai, Yu‐Chun Chuang, Premakumar Yanda, A. Sundaresan, Hemant Singh Kunwar, Vasant Sathe, Ajay Tiwari, D. Chandrasekhar Kakarla, H. D. Yang
Abstract
Complex systems with strongly entangled microscopic degrees of freedom often host a plethora of exotic properties. Herein, we report the unconventional and interesting multiferroic behavior of a layered noncentrosymmetric ferrimagnetic spin-1/2 system, ${\mathrm{Bi}}_{2}{\mathrm{Cu}}_{5}{\mathrm{B}}_{4}{\mathrm{O}}_{14}$. Neutron powder-diffraction study deciphers a robust ferrimagnetic ($\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}\ensuremath{\downarrow}\ensuremath{\downarrow}$) ordering below a temperature ${T}_{C}=25\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which remains unaltered even under a high magnetic field of $H=10\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. Interestingly, two successive ferroelectric transitions are observed, one of which is triggered by the magnetostriction effect and emerges concomitantly with the ferrimagnetic ordering at ${T}_{C}={T}_{E2}=25\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. This is accompanied by a pronounced dielectric peak and a prominent magnetodielectric coupling at ${T}_{C}$. By contrast, other ferroelectric transition commences in the paramagnetic state at ${T}_{E1}=32\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is solely caused by a prominent structural distortion. This strong structural distortion is revealed by the synchrotron x-ray-diffraction study, which is further supported by a concurrent, sharp, anomalous phonon softening observed in the Raman spectra.