Observation of magnetic field-induced second magnetic ordering and peculiar ferroelectric polarization in L-type ferrimagnetic Fe2(MoO4)3

${\mathrm{Fe}}_{2}{({\mathrm{MoO}}_{4})}_{3}$ was synthesized and characterized as a prototype of L-type ferrimagnets (L-FiM) with an ordering temperature ${T}_{\mathrm{N}1}\ensuremath{\sim}12\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ using magnetic susceptibility $(\ensuremath{\chi})$, specific heat $({C}_{\mathrm{p}})$, and dielectric $({\ensuremath{\varepsilon}}^{\ensuremath{'}})$ anomaly. Two remarkable findings are magnetic field $(H)$ induced (i) an additional magnetic phase transition at ${T}_{\mathrm{N}2}$ below ${T}_{\mathrm{N}1}$; and (ii) the emergence of flexible ferroelectric polarization $(P)$ with the tuning parameters $H$ and $T$ below ${T}_{\mathrm{N}2}$. Thus, the H-T phase diagram for spin-induced type-II multiferroics was established. In contrast to some known multiferroics with a critical field-induced spin-flip $P$ below ${T}_{\mathrm{N}1}$, the observed multiferroic nature is exotic. The origin of the profound multiferroic nature may be hidden in the complex $T$-and $H$-dependent spin and lattice structures. Consequently, the schematic picture of $H$-induced possible change of lattice symmetry and conical spin structure has been proposed. More experimental and theoretical works providing solid evidence and interpretations have been suggested to explore these peculiar multiferroic phenomena.