新的磁性材料合成的最新进展导致了新的量子顺磁体的发现。这些材料中的许多,例如钙钛矿Ba $_{4}$ LnMn $_{4}$ O $_{12}$(Ln = Sc或Nb)、Ba $_{3}$ Mn $_{2}$ O $_{8}$和Sr $_{3}$ Cr $_{2}$ O $_{8}$,呈现具有强的簇内相互作用但弱的簇间相互作用的孤立的磁性簇,这延迟了有序到较低温度($T$)的开始。这种局部能量尺度和磁有序温度之间的偏移是磁阻挫的标志。在足够高的$T$下,阻挫团簇磁体的顺磁磁化率($χ$)可以符合居里-外斯定律,但所得的微观参数一般不能与其他方法得到的参数相一致。在这项工作中,我们提出了一个分析微观理论,以获得$χ$的二聚体和三聚体集群磁铁,两个最常见的文献中,利用合适的海森堡型哈密顿。我们还加入了平均场水平上的团簇间相互作用,从而得到了系统临界温度的表达式,并定义了一个新的有效阻挫参数$f_{\text{eff}}$。我们的方法是通过处理一些选定的材料的$χ$数据的例子。
英文摘要:
Recent developments in the synthesis of new magnetic materials lead to the discovery of new quantum paramagnets. Many of these materials, such as the perovskites Ba$_{4}$LnMn$_{4}$O$_{12}$ (Ln = Sc or Nb), Ba$_{3}$Mn$_{2}$O$_{8}$, and Sr$_{3}$Cr$_{2}$O$_{8}$ present isolated magnetic clusters with strong intracluster interactions but weak intercluster interactions, which delays the onset of order to lower temperatures ($T$). This offset between the local energy scale and the magnetic ordering temperature is the hallmark of magnetic frustration. At sufficient high-$T$, the paramagnetic susceptibility ($χ$) of frustrated cluster magnets can be fit to a Curie-Weiss law, but the derived microscopic parameters cannot in general be reconciled with those obtained from other methods. In this work, we present an analytical microscopic theory to obtain $χ$ of dimer and trimer cluster magnets, the two most commonly found in literature, making use of suitable Heisenberg-type Hamiltonians. We also add intercluster interactions in a mean-field level, thus obtaining an expression to the critical temperature of the system and defining a new effective frustration parameter $f_{\text{eff}}$. Our method is exemplified by treating the $χ$ data of some selected materials.
Ab initio calculated diamagnetic and paramagnetic susceptibility of carbonate minerals
Institute of Geophysics of the Czech Academy of Sciences(捷克科学院地球物理研究所);Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University(捷克理工大学核科学与物理工程学院);Faculty of Mathematics and Physics, Charles University(查理大学数学与物理学院)
Different metamagnetism between paramagnetic Ce and Yb isomorphs
为了解决重费米子系统中的变磁现象之谜,我们比较了顺磁同质结构Ce和Yb系统,CeNi $_2$ Ge $_2$和YbNi $_2$ Ge $_2$,它们都位于磁不稳定性附近。最有趣的结果是在脉冲磁场中的磁化测量发现了两个系统中的变磁性转变。这是Ce和Yb类质同象顺磁系统的变磁性的首次观测。类似于其他的变磁体,两种化合物的变磁性转变场都很好地由温度$T_χ^{\rm max}$来缩放,在该温度下磁化率显示出最大值。此外,CeNi $_2$ Ge $_2$的非线性磁化率$χ_3$的峰值出现在$T_χ^{\rm max}/2$附近,与其它重费米子超磁体一样。相反,YbNi $_2$ Ge $_2$在$T_χ^{\rm max}$处仅显示$χ_3$的符号变化,如在位于铁磁临界点附近的巡游变磁体中所观察到的。CeNi $_2$ Ge $_2$的变磁性对应于典型的近藤晶格系统,而YbNi $_2$ Ge $_2$的变磁性类似于近铁磁巡游系统。本文还讨论了YbNi $_2$ Ge $_2$变磁行为的其它可能性。
Effects of hydrostatic pressure on the magnetic susceptibility of ruthenium oxide Sr3Ru2O7: Evidence for pressure-enhanced antiferromagnetic instability
3D XY Universality and Nonlinear magnetic susceptibility in a kagome ice compound
Beihang University(北京航空航天大学);University of Augsburg(奥格斯堡大学);ShanghaiTech University(上海科技大学);RWTH Aachen University(亚琛工业大学);Colorado State University(科罗拉多州立大学);Rutherford Appleton Laboratory(卢瑟福·阿普尔顿实验室);Forshungszentrum Jülich GmbH(于利希研究中心有限公司);Institute of Physics, Chinese Academy of Sciences(中国科学院物理研究所);University of Chinese Academy of Sciences(中国科学院大学)
Magnetic properties of the geometrically frustrated S=1/2 antiferromagnets, La2LiMoO6 and Ba2YMoO6, with the B-site ordered double perovskite structure: Evidence for a Collective Spin Singlet Ground State
Magnon and Spin Transition Contribution in Heat Capacity of Ferromagnetic Cr-doped MnTe: Experimental Evidence for a Paramagnetic Spin-Caloritronic Effect
Dynamic elastic properties and magnetic susceptibility across the austenite-martensite transformation in site-disordered ferromagnetic Ni-Fe-Al alloy
除了允许精确确定铁磁-顺磁相变温度和马氏体生长开始和结束的特征温度外(奥氏体)相以奥氏体为代价(马氏体)相同时冷却(加热),这是广泛的交流磁化率的结果,熔体淬火热弹性马氏体相变的声速和内耗研究(无序)Ni 55 Fe 20 Al 25合金的实验结果为以下结论提供了明确的实验依据。不可逆的热弹性变化(热滞后)发生在奥氏体相的预马氏体制度。在加热循环中,该系统保留了在冷却循环期间在马氏体-马氏体相共存区域中发生的马氏体相的起始和随后生长(以母体奥氏体相为代价)的“记忆”。我们在本文中报告并讨论了这些新的发现。
Local Susceptibility of the Yb2Ti2O7 Rare Earth Pyrochlore Computed from a Hamiltonian with Anisotropic Exchange
稀土烧绿石磁体Yb 2 Ti 2 O 7是少数几种在最低探索温度和远低于居里-外斯温度下显然没有表现出长程序的材料之一。单晶样品上的顺磁中子散射揭示了各向异性相关性的存在,最近的工作导致了这种材料的详细微观哈密顿量的建议,涉及显着的各向异性交换。在这篇文章中,我们从所提出的模型中计算了Yb 2 Ti 2 O 7的局部亚晶格磁化率,并与Cao及其同事的测量结果[Physical Review Letters,{103},056402(2009)]进行了比较,发现非常吻合。与此相反,只有各向同性交换和长距离静磁偶极子的模型引起的局部磁致伸缩性,这是不一致的数据。