Internal magnetic field effect on magnetoelectricity in orthorhombic crystals

Abstract

We have investigated the role of the 4f moment on the magnetoelectric (ME) effect of orthorhombic RMnO 3 (R ¼ rare earth ions). In order to clarify the role of the 4f moment, we prepared three samples: ðEu; YÞMnO 3 without the 4f moment, TbMnO 3 with the anisotropic 4f moment, and ðGd; YÞMnO 3 with the isotropic 4f moment. The ferroelectric behaviors of these samples are different from each other in a zero magnetic field. ðEu; YÞMnO 3 and ðGd; YÞMnO 3 show the ferroelectric polarization along the a axis in the ground state, while TbMnO 3 shows it along the c axis. Such difference may arise from the influence of the anisotropic Tb 3þ 4f moment. The direction of the ferroelectric polarization of RMnO 3 is determined by the internal magnetic field arising from the 4f moment. r 2006 Published by Elsevier B.V.A strong correlation between dielectric and magnetic properties, so-called magnetoelectric (ME) effect, has attracted a revived interest. The series of orthorhombic RMnO 3 (R ¼ rare earth ions) containing TbMnO 3 famous as the ''magnetic-field-induced electric polarization flop'' [1] is a parent material of the colossal magnetoresistance (CMR) manganite. Recently, the noncollinear transverse spiral antiferromagnetic (AF) order of Mn 3d spins is observed between the A-type (EuMnO 3 ) and the E-type (HoMnO 3 ) AF order [2][3][4]. Such unconventional magnetic order is caused by the competition between the ferromagnetic nearest neighbor (NN) interaction and the AF next NN interaction due to the relatively large orthorhombic distortion. Such noncollinear transverse spiral magnetic structure causes the ferroelectric polarization of RMnO 3 [3-6].In previous work, we have investigated the ME effect in (Eu 0:595 Y 0:405 ÞMnO 3 (ðEu; YÞMnO 3 ) without 4f moment [7]. Even if the average ionic radius of R site in ðEu; YÞMnO 3 is the same as that of TbMnO 3 , the direction of the ferroelectric polarization of the ground state of ðEu; YÞMnO 3 is different from that of TbMnO 3 in a zero magnetic field: ðEu; YÞMnO 3 shows the ferroelectric polarization along the a axis (P a ), while TbMnO 3 shows P c . It is considered that this difference is attributed to the magnetic property of each R ion.In this paper, we have revealed the role of the rare-earth 4f moment on the ME effect of orthorhombic RMnO 3 . In order to investigate the role of the 4f moment, we prepared three samples: ðEu; YÞMnO 3 without the 4f moment, TbMnO 3 with the anisotropic 4f moment, and (Gd 0:69 Y 0:31 ÞMnO 3 (ðGd; YÞMnO 3 ) with the isotropic 4f moment. The average ionic radius of R site in these samples is fixed to be same as that of TbMnO 3 .The compositional ratio of the Eu 3þ to Y 3þ ions and that of Gd 3þ to Y 3þ were obtained by a calculation based on the Shannon's ionic radius table [8]. The single crystal sample was grown by the floating zone method. We performed X-ray diffraction and rocking curve measurements on the resulting crystal at room temperature, and confirmed that the samples have the orthorhombic Pbnm structure without any impurity phases ...

Double-exchange theory of ferroelectric polarization in orthorhombic manganites with twofold periodic magnetic texture

“…For example, such a behavior is typical for the Eu 1−x Y x MnO 3 compounds, composed from nonmagnetic rare-earth elements. 2,39 The results of this section suggest that this behavior is more generic and can be anticipated in other regimes, including twofold periodic magnetic systems. The origin of this phenomenon is related to the specific symmetry of the crystal (in our case, the orthorhombic P bnm symmetry) and how it is lowered by the magnetic order.…”

The physics of magnetoelectric composites

“…Examples of single phase multiferroic materials are: Cr 2 O 3 which exhibits magnetoelectric behavior applying a rather high external magnetic field (H410 T) [6]; materials such as RMnO 3 (R ¼ Eu, Gd, Tb) [7], BiMnO 3 [8], BiFeO 3 [9]; and also other structure types such as GdFe 3 (BO 3 ) 4 [10]. All these materials exhibit magnetoelectric behavior, however, at low temperatures and sometimes even at high external field.…”

Fabrication and Magnetic Properties of SrTiO3/ SmCoFe2O4composite Nanoparticles

“…Ferrite based materials are the most widely used as magnetic materials with excellent chemical stability and their production is relatively cheap. There are two types of (ME) materials, the single phase compounds [20][21][22][23][24][25] and the ME composites which are materials with good magnetic properties can be combined with materials with piezoelectric properties leading to (ME) composites even at room temperature [26]. The main focus of this work is to study the magnetic properties of (y) STO / (1-y) SCFO nanocomposite prepared by citrate precursor method.…”