The coexistence and coupling of magnetic and ferroelectric orderings in single phase multiferroics has evinced enormous scientific interest as it involves breaking of time reversal and space inversion symmetries in the same material. The mutual controllability of the two diverse orderings in multiferroics has potential for developing new generation multifunctional sensor, actuator and data storage devices. We present here evidence for a new exotic facet of multiferroicity, whereby one can raise the strength of antiferromagnetic (AFM) superexchange interaction and hence tune the Néel temperature (TN) from ~120K in bulk to ~350K in 18nm size particles by tuning the ferroelectric distortion in the tetragonal phase of multiferroic (1-x)BiFeO3 -xPbTiO3 solid solutions . This observation is unique to multiferroics only as the TN in non-multiferroic AFM oxides decreases with particle size. Our results provide a scientific basis for designing room temperature single phase multiferroics, useful for making multifunctional device operating at room temperature.
First principles study of the multiferroics BiFeO$_{3}$, Bi$_{2}$FeCrO$_{6}$, and BiCrO$_{3}$: Structure, polarization, and magnetic ordering temperature
Possible coexistence of Cycloidal Phases, Magnetic Field Reversal of Polarization and Memory Effect in Multiferroic \emph{R}$_{0.5}$Dy$_{0.5}$MnO$_3$ (\emph{R}=Eu and Gd)
我们报告的\emph{ab}和\emph{bc}摆线有序的Mn自旋在不同的温度和它们可能在低温共存的多晶混合稀土化合物，\emph{R} $_{0.5}$ Dy $_{0.5}$ MnO $_3$（\emph{R} = Eu和Gd），这表现出非凡的磁电性能的发生。虽然Gd $_{0.5}$ Dy $_{0.5}$ MnO $_3$的极化与TbMnO $_3$相当，但化合物Eu $_{0.5}$ Dy $_{0.5}$ MnO $_3$显示出高的极化值。然而，这两种材料都表现出巨大的磁可调谐性，并表现出大的磁电容，其符号在两个摆线有序温度之间变化。有趣的是，在磁场斜升或斜降时，电极化可以反转，这对于任何\emph{R} MnO $_3$系统都没有观察到。最引人注目的是，这些化合物甚至在顺电和顺磁区（T $_C$ $\leq$ T $\leq$ 80 K）显示非易失性铁电存储效应。我们将这些显著的性质归因于\emph{ab}和\emph{bc}摆线有序相的共存。
