弛豫多铁性材料研究进展

doi:10.15541/jim20160644

摘要/Abstract

摘要：

多铁性材料同时具有多种铁性(铁电性、铁磁性或铁弹性)的有序, 可实现电磁信号的相互控制, 成为近年来研究热点。在具有成分无序的复杂体系中, 长程铁性有序有可能被打破, 材料将表现出弛豫特性。我们将至少存在一种铁性弛豫特性的多铁性材料称之为弛豫多铁性材料。这类多铁性材料的极化强度(或磁化强度)在外加电场(或外加磁场)作用下响应更加灵敏, 其磁电耦合机制与长程有序的多铁性材料不同。本文结合国内外最新研究成果, 首先介绍了和弛豫铁性有序相关的物理概念, 重点阐述了多铁性材料在铁电和铁磁双弛豫态下的磁电耦合机制; 然后, 详细介绍了钙钛矿结构(包括PbB₁B₂O₃基和BiFeO₃基材料)和非钙钛矿结构(包括层状Bi结构和非正常铁电体)弛豫多铁性材料的研究进展; 最后, 对该领域亟待解决的问题进行了展望。

关键词: 弛豫性, 多铁性材料, 磁电耦合, 纳米存储器件

Abstract:

The multiferroic material, which shows the coexistences of multi ferroic orders (ferroelectricity, ferromagnetism or ferroelasticity), can realize the mutual control of the electric and magnetic signals, and becomes one of the hottest research topics. The long-range ferroelectric or ferromagnetic order may be broken in compositionally disordered systems. In this situation, it is posssible that materials display relaxor behavior. Multiferroic materials possessiong at least one ferroic relaxor character can be named as relaxor multiferroics. The polarization (or magnetization) is very sensitive to the applied electric field (or magnetic field). Besides, the magnetoelectric coupling effect of relaxor multiferroics is different from that of multiferroics with long ferroic orders. In this paper, the most recent and important theoretical and experimental advances in this new research field are reviewed. Firstly, basic physical concepts of the relaxor ferroic orders and the different mechanism of the magnetoelectric coupling effect on materials are introduced with the coexistence of relaxor ferroelectric ordering and relaxor magnetic ordering. Then, the recent researches on two sorts of the relaxor multiferroics, including perovskite (PbB₁B₂O₃based and BiFeO₃ based) and non-perovskite (Bi-layered based and improperly ferroelectric based) structural materials, are reviewed. Finally, the further development of relaxor multiferroics is prospected.

Key words: relaxor behavior, multiferroics, magnetoelectric coupling effect, nano memory device

中图分类号:

TQ174

魏永星, 靳长清, 曾一明. 弛豫多铁性材料研究进展[J]. 无机材料学报, 2017, 32(10): 1009-1017.

WEI Yong-Xing, JIN Chang-Qing, ZENG Yi-Ming. Progress of Relaxor Multiferroic Materials[J]. Journal of Inorganic Materials, 2017, 32(10): 1009-1017.

图/表 10

图1 典型弛豫铁电体Pb(Nb2/3Mg1/3)O3不同频率下介电常数与温度关系[13]

Fig. 1 Temperature dependence of dielectric constant for classical relaxor ferroelectrics Pb(Nb2/3Mg1/3)O3 at various frequencies[13]The classical relaxor ferroelectrics display the broad, frequency-dependent dielectric anomalies. The value of the maximum dielectric constant εm could reach above 10,000. The relation between the Tm and frequency could be described by V-F function

图2 顺磁态、长程磁有序态(铁磁、亚铁磁和反铁磁)及自旋玻璃态示意图

Fig. 2 Schematic representation of paramagnetic state, long- ranged magnetic state (ferromagnetic, ferrimagnetic, antiferromagnetic) and spin glass state

表1 PbB1B2O3基弛豫多铁材料磁电特性

Table 1 Polar and magnetic orderings of the PbB1B2O3 based multiferroic materials

Compositions	Polar ordering	Magnetic ordering
PbFe_2/3W_1/3O₃ crystals^[31]	Ferroelectric relaxor T_m= 210 K @0.1 MHz T_f = 164 K	Anti-ferromagnetic T_N = 350 K Magnetic glass state T_g= 10 K
PbFe_0.5Nb_0.5O₃ceramics^{[23, 29]}	Ferroelectric T_m=373 K	Anti-ferromagnetic T_N = 153 K Magnetic glass state T_g= 10.6 K
PbFe_0.5Ta_0.5O₃ceramics^{[27, 30]}	Ferroelectric T_m = 259 K	Anti-ferromagnetic T_N = 153 K Magnetic glass state T_g< 10 K
0.8PbFe_1/2Nb_1/2O₃-0.2PbMg_1/2W_1/2O₃ceramics^[32]	Ferroelectric relaxor T_m = 280 K @0.1 MHz T_f= 245 K	Magnetic glass state T_g= 25K
Pb(Fe_0.66W_0.33)_0.8 Ti_0.2O₃ thin films^[33]	Ferroelectric relaxor T_m = 350 K @10 kHz T_f = 238 K	Ferrimagnetic
Pb(Fe_0.66W_0.33)_0.2 (Zr_0.53Ti_0.47)_0.8O₃thin film^[36]	Ferroelectric relaxor T_m < 600 K @1 MHz	Ferrimagnetic
Pb(Zr_0.53Ti_0.47)_0.60(Fe_0.5Ta₀.₅)_0.4O₃ thin films^[37]	Ferroelectric relaxor T_m = 390 K @1 MHz T_f= 305 K	Ferrimagnetic

表2 BiFeO3基弛豫多铁材料磁电特性

Table 2 Polar and magnetic orderings of the BiFeO3 based multiferroic materials

Compositions	Polar ordering	Magnetic ordering
Bi(Fe_0.5Mn_0.5)O₃thin films^[45]	Ferroelectric relaxor T_m = 440 K @1 MHz T_f = 314 K	Magnetic glass state T_f2=122 K
0.65BiFeO₃- 0.35BaTiO₃ceramics^[47]	Ferroelectric relaxor T_m= 687 K @1 MHz	Ferrimagnetic
0.67BiFeO₃- 0.33BaTiO₃ single crystal^[50]	Ferroelectric relaxor T_m = 650 K @0.1 MHz	Magnetic glass state
0.5Bi(Fe_0.5La_0.5)O₃- 0.5PbTiO₃ ceramics^[54]	Ferroelectric relaxor T_m = 520 K @0.1 MHz	Ferrimagnetic
0.6BiFeO₃- 0.4Bi_1/2K_1/2TiO₃ceramics^[55-56]	Ferroelectric relaxor T_m= 703 K @0.1 MHz	Ferrimagnetic T_N< 500 K
0.4BiFe_0.9Co_0.1O₃- 0.6Bi_1/2K_1/2TiO₃ceramics^[59]	Ferroelectric relaxor T_m= 693 K @0.1 MHz T_f < 573 K	Ferrimagnetic T_N= 670 K

图3 PbFe2/3W1/3O3中Fe3+自旋排列示意图, 在反铁磁子晶格中存在挫败的Fe3+的自旋[31]

Fig. 3 Schematic representation of Fe3+ spins arrangement for PbFe2/3W1/3O3, The frustrated Fe3+ spins appear in AFM sublattices[31]

图4 Pb(Fe0.66 W0.33)0.2(Zr0.53Ti0.47)0.8O3在磁场作用下的(a)极化强度-电场曲线及(b)介电常数实部虚部与频率的关系[35]

Fig. 4 (a) The P-E loops and (b) the real and imaginary part of dielectric constant as a function of frequencies with various magnetic fields for Pb(Fe0.66 W0.33)0.2(Zr0.53Ti0.47)0.8O3[35]Increase of the magnetic field H leads to decrease in Pr. Pr is nearly zero when H reaches 0.5 T. This effect disappears after magnetic field being removed. Correspondingly, the anomaly peak of the imaginary part for dielectric constant shifts to the low frequency side with H increasing, which reveals the increase of the relaxation time

图5 基于弛豫多铁性材料的多态存储器

Fig. 5 Relaxor multiferroics for multi-states memory device

图6 0.67BiFeO3-0.33BaTiO3单晶(a)(112)衍射面在600 K时的漫反射强度等高线和(b)在不同温度下的M-H曲线[50]

Fig. 6 (a) Contour plots of the diffuse intensities at 600 K around the (112) reflection and (b) M-H loops at various temperatures for the single crystal of 0.67BiFeO3-0.33BaTiO3[50] The crystal shows the strong nuclear diffuse scattering, with a correlation length of 8 nm. It demonstrates the existence of the PNR. The M-H loops display the character of super-paramagnetism. The super-paramagnetism could be related to the short magnetic state. The fitting of Langevin function reveals the size of the short magnetic state is in the range of 8-9 nm

图7 磁场作用下的同步压力电显微镜实验[60]

Fig. 7 In situ PFM under magnetic field experiments[60]The polarization switches obviously in the regions marked by blue and red rectangles

图8 Bi5Ti3FeO15 (a)晶体结构(b)STEM图谱和(c)原子占位信息示意图[68-69]

Fig. 8 (a) Crystal structure, (b) STEM pattern and (c) schematic illustration of atom position information of Bi5Ti3FeO15[68-69]The crystal structure is obtained from ref [68]. Between the two [Bi2O2]2- layers, there are four Ti(Fe)O6 octahedra. The STEM measurement demonstrates Ti/Fe atoms shift from ideal position along [110]

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