Multiferroicity in B-site ordered double perovskite Y2MnCrO6

Double perovskite manganite Y2MnCrO6 ceramic Novel multiferroic properties are displayed with respect is synthesized and its multiferroic properties are investigated. to other multiferroics, such as high ferroelectric phase transi- tion temperature, and the coexistence of ferrimagnetism and ferroelectricity. Moreover, the ferroelectric polarization of Y2MnCrO6 below the magnetic phase temperature can be effectively tuned by an external magnetic field, showing a re- markable magnetoelectric effect. These results open an effective avenue to explore magnetic multiferroics with spontaneous magnetization and ferroelectricity, as well as a high ferroelectric transition temperature.     

Ferrimagnetism and metal–insulator transition in an organic polymer chain

The ferrimagnetism and quantum phase transition of a bipartite lozenge periodic Anderson-like organic polymer, in which the localized f electrons hybridize with the odd site conduction orbitals, are investigated by means of Green＇s function theory. The ground state turns out to be gapless ferrimagnetism. At a finite temperature, the ferrimagnetic-to- paramagnetic phase transition takes place. The Kondo screenings and Ruderman-Kittel-Kasuya-Yosida （RKKY） inter- action can reduce and increase the transition temperature, respectively. Two Kondo screenings compete with each other, giving rise to the localized f electron spin screened antiferromagnetically. Accordingly, in a magnetic field, all spins are aligned along the chain easily, which is associated with metal-insulator transition. Furthermore, in a temperature-field plane, we reveal the gapless and spin polarized phases, which are characterized by susceptibility and specific heat, and whose behaviours are determined by the competition between the up-spin and down-spin hole excitations.     

阻挫诱导的亚铁磁性Heisenberg系统中的量子相变

利用密度矩阵重整化群(DMRG)方法研究磁性阻挫对一种S=1/2准一维反铁磁自旋链但却具有亚铁磁性的Heisenberg系统基态的影响.计算了单个晶胞的基态能、自旋关联函数以及自旋能隙.研究表明这种Heisenberg自旋系统的基态随着阻挫α的增强将从磁有序相变化到自旋无序相,并且伴随着自旋能隙的出现,量子相变点为α≈0.412.同时线形链上格点间自旋长程关联值的计算结果表明在磁有序区间体系的磁有序性质随着α的增强而减弱,阻挫在0≤α< 关键词： 准一维反铁磁自旋链 亚铁磁性 密度矩阵重整化群 自旋能隙     

Magnetic Properties of Ferromagnetic Double Layers with Ferrimagnetic Interlayer Coupling at Zero Temperature

Spin-wave theory is used to study magnetic properties of ferromagnetic double layers with a ferrimagnetic interlayer coupling at zero temperature. The spin-wave spectra and four sublattices magnetizations and internal energy are calculated by employing retarded Green function technique. The sublattice magnetizations at ground state are smaller than their classical values, owing to the zero-point quantum fluctuations of the spins.     

非双交换作用巨磁电阻材料Fe1+xCr2-xS4的磁性

Fe1+xCr2-xS4(x=0,0.1)是不存在双交换作用和Jahn-Teller畸变的巨磁电阻材料,Missbauer谱指认,对于FeCr2S4,Fe离子以Fe2+形式占据在四面体间隙形成Fe亚晶格,Cr离子以Cr3+的形式占据八面体间隙形成Cr亚晶格;对于Fe1.1Cr1.9S4,过量的的Fe离子替代Cr离子以Fe3+形式存在.电子自旋共振的结果表明在居里温度Tc以上,两个样品都只有单一吸收峰,而在T1以下(T1对应于Tc以下电阻率最小值的温度),ESR谱中原始的顺磁峰同时劈裂为一支高场峰和一支低场峰.该体系的微观磁性显示,对于FeCr2S4,Fe、Cr亚晶格的自旋同时进入铁磁态,而这两个亚晶格的磁矩彼此反平行排列;对于Fe1.1Cr1.9S4,过量的Fe离子的自旋反平行于Cr离子,这不但削弱了Cr亚晶格的内场,同时也使两个亚晶格之间的耦合减弱.由此,Fe1+xCr2-xS4反常的输运行为可以被很好地理解.