Ferrielectricity in DyMn₂O₅: A golden touchstone for multiferroicity of RMn₂O₅ family

Abstract

The RMn 2 O 5 manganite compounds represent one class of multiferroic family with magnetic origins, which has been receiving continuous attention in the past decade. So far, our understanding of the magnetic origins for ferroelectricity in RMn 2 O 5 is associated with the nearly collinear antiferromagnetic structure of Mn ions, while the exchange striction induced ionic displacements are the consequence of the spin frustration competitions. While this scenario may be applied to almost all RMn 2 O 5 members, its limitation is either clear: the temperature-dependent behaviors of electric polarization and its responses to external stimuli are seriously materials dependent. These inconsistences raise substantial concern with the state-of-the-art physics of ferroelectricity in RMn 2 O 5 . In this mini-review, we present our recent experimental results on the roles of the 4f moments from R ions which are intimately coupled with the 3d moments from Mn ions. DyMn 2 O 5 is a golden figure for illustrating these roles. It is demonstrated that the spin structure accommodates two nearly collinear sublattices which generate respectively two ferroelectric (FE) sublattices, enabling DyMn 2 O 5 an emergent ferrielectric (FIE) system rarely identified in magnetically induced FEs. The evidence is presented from several aspects, including FIE-like phenomena and magnetoelectric responses, proposed structural model, and experimental check by nonmagnetic substitutions of the 3d and 4f moments. Additional perspectives regarding possible challenges in understanding the multiferroicity of RMn 2 O 5 as a generalized scenario are discussed.

Understanding the multiferroicity in TmMn2O5 by a magnetically induced ferrielectric model

“…P IC , against magnetic field H , is much more remarkable than that of polarization P C between T N1 and T N2 . This effect fits the scenario of P IC  ~ ( S i × S j ), noting that the noncollinear spin structure is usually more sensitive to varying H than the collinear structure3638.…”

“…It has been repeatedly confirmed that the Mn spin orders in RMn 2 O 5 systems are highly robust against external magnetic field383940. A magnetic field of several Tesla seems not to shake much the Mn spin orders.…”

“…5(c), indicating clearly the appearance of a negative polarization around T N1 , the polarization flop from negative value to positive one around T N2 , and another FE transition around T Tm , respectively. This polarization flop is the character of a typical FIE system2938.…”

“…In fact, systematic investigations on the behaviors of P ( T , H ) in polycrystalline DyMn 2 O 5 were performed recently using the highly sensitive pyroelectric current technique293839. The main polarization can be illustrated by a FIE model, in which consists of two roughly antiparallel polarization components.…”

Giant magnetocaloric effect in an exchange-frustrated GdCrTiO5 antiferromagnet

“…Besides magnetoelectric properties, RMn 2 O 5 shows the ability to be a good magnetic refrigerant at cryogenic temperature. 29,[33][34][35][36] However, the members of the family RCrTiO 5 isostructural to RMn 2 O 5 were paid very little attention. [37][38][39] In orthorhombic RCrTiO 5 , the Cr 3+ ions are interspaced between the R 3+ and Ti 4+ ions and the Cr 3+ spins are collinear along the crystallographic c axis whereas the moments of R 3+ lie on the ab plane.…”