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Possible ground states and parallel magnetic-field-driven phase transitions of collinear antiferromagnets (可能的基态和平行磁场驱动的共线反铁磁物质的相变)
发布时间:2016-11-11

Possible ground states and parallel magnetic-field-driven phase transitions of collinear antiferromagnets (可能的基态和平行磁场驱动的共线反铁磁物质的相变)

Hai-Feng Li
npj Computational Materials
 2, Article number: 16032 (2016)
doi:10.1038/npjcompumats.2016.32
Published online:14 October 2016
Abstract| Full Text | PDF OPEN

摘要:理解所有可能的基态性质,尤其是磁场驱动相变的反铁磁体基态性质,是揭示一些如超导、多铁性或磁致电阻等有趣现象背后本质的重要一环。本研究所作的相容平均场计算,赋予反铁磁(AFM)交换作用(J)、易轴各向异性(γ)、单轴单离子各向异性(D)以及一个平行于AFM易轴磁场的Zeeman耦合几个变量,始终保持了AFM态、自旋-翻牌(SFO)和自旋-反转转变三者统一。计算结果发现,数学上允许的一些奇特自旋态和奇特脉动取决于相对耦合强度(J, γ, D)。本研究建立了三维(J, γ, D)和二维(γ, D)相图,可清楚地显示平衡相条件,同时本文还讨论了各种磁性态的起源及其在不同耦合中的转换。除传统的一级SFO过渡类型外,本研究明确了二级SFO过渡类型的存在。这些研究为共线反铁磁体磁态(带有两个互相贯通的亚点阵结构)提供了一个完整的理论模型,也为估算磁交换参数(J, γ, D)提供了一个实用的替代方法,有可能为揭示块材、薄膜和相关电子体系的纳米结构的非平凡磁相关性能,提供理论指导。

Abstract: Understanding the nature of all possible ground states and especially magnetic-field-driven phase transitions of antiferromagnets represents a major step towards unravelling the real nature of interesting phenomena such as superconductivity, multiferroicity or magnetoresistance in condensed-matter science. Here a consistent mean-field calculation endowed with antiferromagnetic (AFM) exchange interaction (J), easy axis anisotropy (γ), uniaxial single-ion anisotropy (D) and Zeeman coupling to a magnetic field parallel to the AFM easy axis consistently unifies the AFM state, spin-flop (SFO) and spin-flip transitions. We reveal some mathematically allowed exotic spin states and fluctuations depending on the relative coupling strength of (J, γ and D). We build the three-dimensional (J, γ and D) and two-dimensional (γ and D) phase diagrams clearly displaying the equilibrium phase conditions and discuss the origins of various magnetic states as well as their transitions in different couplings. Besides the traditional first-order type one, we unambiguously confirm an existence of a second-order type SFO transition. This study provides an integrated theoretical model for the magnetic states of collinear antiferromagnets with two interpenetrating sublattices and offers a practical approach as an alternative to the estimation of magnetic exchange parameters (J, γ andD), and the results may shed light on nontrivial magnetism-related properties of bulks, thin films and nanostructures of correlated electron systems.

Editorial Summary Quantum matter: Mapping magnetic materials (量子物质:为磁性材料绘图)

来自中国的研究人员证实了可更好地理解磁性材料奇异性能的数学方法。澳门大学的李海峰(Hai-Feng Li)开发了一种计算方法,它能预测所谓关联物质从一某种状态转变成另一种状态的途径。之所以称为关联物质,是因为它们内部的电子都彼此相互作用,并能造成物质的非凡性能,如超导、多铁性和大磁电阻效应。对这些材料施加磁场可以使其从诸多状态(或相)中的一种转变成另一种。Li的这一理论框架将合作性和竞争性电子相互作用结合起来,用以预测物质的相转变。基于这一理论,可为所有平衡相画出一张地形图,加深对各种磁性态起源的了解。

A mathematical method for better understanding the exotic properties of magnetic materials is demonstrated by researchers in China. Hai-Feng Li from the University of Macao has developed calculations that predict the way so-called correlated matter can change from one state to another. Correlated materials are so called because the electrons within them all interact with each other to give the substance extraordinary properties. These include superconductivity, multiferroicity and large magneto-resistance effects. Applying a magnetic field to such materials can make it switch from one of these states, or phases, to another. Li’s theoretical framework combines both cooperative and competitive electron interactions to predict these phase changes. With this, a map of all equilibrium phases can be derived, and this provides insight into the origins of the various magnetic states.

 
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