Multiferroic properties of exotic double perovskite A2BB' O6

Abstract

Multiferroic material in which there co-exist at least two of the ferro-phases,namely ferroelectricity,(anti-) ferromagnetism,and ferroelasticity,has attracted considerable attention in recent years due to its intriguing physics and potential applications for advanced multifunctional devices.However,multiferroic materials are rare due to the contradictory requirements between electrical polarization and magnetism.So far,only several compounds have been reported to show above-room temperature multiferroics.Thus,it is essential to search for new materials.The two most significant strategies to obtain multiferroics are 1) to incorporate magnetic transition-metal ions into polar structures to obtain polar magnets,and 2) to introduce special magnetic structure to drive ferroelectricity (the so-called type-Ⅱ multiferroics).Exotic double perovskite-related oxide A2BB'O6 with small A-site cations is one of the most extensively studied multiferroic families in recent years. The small A-site cations give small perovskite tolerance factor (t),and mostly high-pressure synthesis is required to stabilize the exotic perovskite structure.The crystal structure of exotic A2BB' O6 oxides can crystallize into either the centrosymmetric alumina corundum (AL),ilmenite (IL),or distorted GdFeO3-type perovskite structure,or the polar LiNbO3(LN),Ni3TeO6(NTO),or ordered ilmenite (OIL) structure.The polar LN,NTO,and OIL structures can accommodate magnetic transition-metal ions at both the A and B/B'sites in octahedral coordination,giving enhanced magnetic interactions and thus robust magneto-electric effect and high spontaneous polarization as well (usually above 50 C/cm-2,more than twice that in the renown BaTiO3),examples include the LN-type Mn2FeNbO6,and Mn2FeTaO6,OIL-type Mn2FeMoO6,and NTO-type Mn2FeMoO6,Mn2FeWO6,and Mn2MnWO6.These polar magnets show potential multiferroic responses even above room temperature (e.g.,ferromagnetic ordering temperature up to 340 K in NTO-type Mn2FeMoO6) and magnetoelectric coupling effect as in Mn2MnWO6.Magnetoelectric coupling can also arise in centrosymmetric IL structure in the absence of helical spin structure,such as those that are observed in Mn2FeSbO6,which exhibits colinear ferrimagnetic spin arrangement but magnetostriction induced antiferroelectricity.The corundum derivatives (AL,LN,IL,OIL,and NTO) and perovskite phases are competitive,depending on the electron configuration and synthesis pressure,and usually higher pressure favors the formation of perovskite structure.Compared with polar magnets in the corundum family,the exotic double perovskite adopts distorted GdFeO3-type structure (P21/n) with eight-coordination of the A-sites.In some double perovskite materials,the electric polarization can be induced by the special magnetic order,such as the ⇈⇊ magnetic structure induced type-Ⅱ multiferroics exemplified by A2CoMnO6(A=Lu,Y,Yb,Lu).In this review paper,we first compare the structure features of conventional and exotic double perovskite A2BB'O6 derived from the simple ABO3 analog,then summarize the recent progress of multiferroics in exotic double perovskite family,such as the polar magnets with transition-metal (Mn and Ni) cations at the A sites,type-Ⅱ multiferroic Mn2FeSbO6,and A2CoMnO6(A=Lu,Y,Yb,Lu). Finally,the problems and prospection of multiferroics in exotic double perovskite A2BB'O6 are also discussed to give a reference for the future research.