Sangeetha N S, Pakhira Santanu, Ding Qing-Ping, Krause Lennard, Lee Hyung-Cheol, Smetana Volodymyr, Mudring Anja-Verena, Iversen Bo Brummerstedt, Furukawa Yuji, Johnston David C
Ames Laboratory, Iowa State University, Ames, IA 50011.
Department of Physics and Astronomy, Iowa State University, Ames, IA 50011.
Proc Natl Acad Sci U S A. 2021 Nov 2;118(44). doi: 10.1073/pnas.2108724118.
SrMnP and CaMnP are insulators that adopt the trigonal CaAlSi-type structure containing corrugated Mn honeycomb layers. Magnetic susceptibility and heat capacity versus temperature data reveal a weak first-order antiferromagnetic (AFM) transition at the Néel temperature [Formula: see text] K for SrMnP and a strong first-order AFM transition at [Formula: see text] K for CaMnP Both compounds exhibit isotropic and nearly -independent [Formula: see text], suggesting magnetic structures in which nearest-neighbor moments are aligned at [Formula: see text] to each other. The P NMR measurements confirm the strong first-order transition in CaMnP but show critical slowing down above [Formula: see text] for SrMnP, thus also evidencing second-order character. The P NMR measurements indicate that the AFM structure of CaMnP is commensurate with the lattice whereas that of SrMnP is incommensurate. These first-order AFM transitions are unique among the class of (Ca, Sr, Ba)Mn (P, As, Sb, Bi) compounds that otherwise exhibit second-order AFM transitions. This result challenges our understanding of the circumstances under which first-order AFM transitions occur.
SrMnP和CaMnP是绝缘体，它们采用含有波纹状Mn蜂窝层的三角CaAlSi型结构。磁化率和热容量随温度变化的数据表明，SrMnP在奈尔温度[公式：见正文]K处有一个微弱的一级反铁磁（AFM）转变，而CaMnP在[公式：见正文]K处有一个强烈的一级AFM转变。两种化合物都表现出各向同性且几乎与[公式：见正文]无关，这表明其磁结构中最近邻磁矩相互对齐的角度为[公式：见正文]。P NMR测量证实了CaMnP中的强烈一级转变，但显示出SrMnP在[公式：见正文]以上存在临界慢化，因此也证明了其二级特性。P NMR测量表明，CaMnP的AFM结构与晶格是相称的，而SrMnP的则是不相称的。这些一级AFM转变在（Ca，Sr，Ba）Mn（P，As，Sb，Bi）化合物类别中是独特的，否则这些化合物会表现出二级AFM转变。这一结果挑战了我们对一级AFM转变发生情况的理解。
