Figure 1. BiMn at room temperature 3Cr 4O12A-site ordered perovskite crystal structure (space group Im-3), and (b) synchrotron radiation X-ray diffraction patterns.
Figure 2.BiMn 3Cr 4O12(A) the susceptibility and its Curie-Fes law fit; (b) the specific heat and dielectric constant; (c) the pyroelectric and electric polarization; (d) the magnetization curve ; (e) pyroelectric low temperature; (f) low temperature electric polarization.
Figure 3.BiMn
3Cr
4O
12The hysteresis loop at different temperatures shows a large electrical polarization.
Figure 4. Magnetic Field Pair BiMn
3Cr
4O
12The regulation of electrodeposition shows a strong magneto-electric coupling effect.
Figure 5.BiMn
3Cr
4O
12Magnetoelectric phase diagram at different temperatures PM = paramagnetic, PE = paraelectric, FE = ferroelectric, MF = ferroelectric.
Magnetoelectric multiferroic material refers to a kind of multi-functional material that has both magnetic ordering and electrode ordering. By utilizing two kinds of ordered coexistence and mutual coupling, it is possible to realize magnetic field regulation and electric polarization or electric magnetic field change. As a promising material for spintronic materials, extensive research is expected to be used for next-generation information memory, tunable microwave signal processor, and ultra-sensitive magnetoelectric sensors, etc. Depending on the origin of the polarization, Ferroelectric materials are classified into the first type of multiferroids and the second type of multiferroids.In the first type of multiferroic materials, the ferroelectric polarization has different origins from the magnetic order, so that although the polarization of such materials may be Will be relatively large, but the magneto-electric coupling is small.The second kind of multi-iron material's electric polarization is caused by the special spin structure breaking space inversion symmetry, so these materials have strong magnetoelectric coupling, Is that the electric polarization is often weak, and the practical application requires that the material has both large electric polarization and strong magneto-electric coupling effect, but this compatibility is hard to exist in the conventional single-phase multi-iron materials. Looking for single-phase multiferroic materials with the excellent performance of both the urgent and challenging scientific problems.
Recently, the Chinese Academy of Sciences Institute of Physics / Beijing Condensed Matter Physics Laboratory (Preparatory) Extreme Condition Physics Laboratory EX6 researcher Longyou Wen research team, using unique high temperature and pressure technology for the first time prepared with A-bit ordered perovskite Structure of the BiMn 3Cr 4O12System, and it is rare to find that the single-phase material has both large electric polarization and strong magneto-electric coupling effect.
Previous studies have shown that in the A-site ordered perovskite of chemical formula AA'3B4O12, the transition metal ions can be accommodated simultaneously because of A 'and B sites. Therefore, the structure and magnetoelectric properties of the material can be controlled by selecting suitable ion combinations , Thus inducing magnetoelectricity of multiferroic.Under the guidance of this train of thought, the researchers designed a new A-site ordered perovskite material BiMn 3Cr 4O12, And the compound was obtained under the conditions of high pressure and high temperature of 8GPa and 1100C.The magnetic susceptibility, magnetization, specific heat, dielectric constant, electric polarization, hysteresis loop, high resolution electron microscope, synchrotron X-ray diffraction And absorption spectra, neutron diffraction and a series of comprehensive structural characterization and physical properties testing, combined with first-principles theory calculations, the researchers conducted a detailed study of the system.As the temperature decreases, BiMn 3Cr 4O12A ferroelectric phase transition has been experienced at 135 K. Since the phase change temperature attachment material has not yet been spin-ordered, the phase transition of the ferroelectric has nothing to do with the magnetic order, further X-ray refinement of cryogenic synchrotron radiation results and theoretical calculations show that, Bi 3+The lone pair electron effect of the ions is responsible for the phase transition of the ferroelectric material, a significant hysteresis loop is observed below the phase transition temperature of the ferroelectric material and leads to the occurrence of large electric polarization (more than the classical class II ferroalloys The material is two orders of magnitude.) When the temperature is reduced to 125K, BiMn 3Cr 4O12Undergoing an antiferromagnetic phase transition, neutron diffraction proved that the antiferromagnetic transition originates from the B site Cr 3+Ionic G-type long-range anti-ferromagnetic order, and A 'bit of Mn 3+Ion has not yet formed magnetic order below 125K, long-range magnetic order coexist with ferroelectric polarization, but the anti-ferromagnetic order can not induce electric polarization, so the material into the first class with large electric polarization iron Phase.When the temperature continues to decrease to 48K, the Mn3 + ions at A 'also achieve G-type long-range antiferromagnetic ordering, and the Mn3 + ions at A' 3+The spin-ordered structure of the ions together leads to the formation of a group of polarized magnetic dots, which can break the symmetry of space inversion, so the antiferromagnetic phase transition at 48K induces another ferroelectric phase transition with strong magnetoelectric coupling Effect occurs, this time at the same time the material presents a second type of multi-iron phase.Thus, the low temperature BiMn 3Cr 4O12Contains both the first type of multi-iron phase and the second type of multi-iron phase, so that the large electric polarization and strong magneto-electric coupling effect are simultaneously achieved in this single-phase multi-iron material, breaking through the two previous effects Uncomparable bottlenecks in single-phase materials are driving the potential use of multiferroic materials.
Relevant research results published in Advanced Materials, and was selected as Inside Cover. Research work has been extensive cooperation between domestic and foreign counterparts, the theoretical calculations and Dongsai University professor Dong Shuai cooperation, powder neutron diffraction and the United States Oak Ridge National Laboratory doctor H. Cao and S. Calder. Synchrotron radiation X-ray diffraction was completed in collaboration with Professor Y. Shimakawa's group at Kyoto University. Electron microscopy was done in collaboration with Professor M. Azuma's group at Tokyo Institute of Technology. SUN Yang, a researcher at the Institute of Physics, Chinese Academy of Sciences, Associate researcher Chai Yisheng held a useful discussion on the work.
Research has won the support of the Ministry of Science and Technology, the National Natural Science Foundation of China, the Chinese Academy of Sciences and so on.
