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arXiv · 2105.02394

First-order transitions at the Neel temperatures of trigonal SrMn2P2 and CaMn2P2 single crystals containing corrugated-honeycomb Mn sublattices

N. S. Sangeetha·Santanu Pakhira·Q. -P. Ding·H. -C. Lee·V. Smetana·A. -V. Mudring·Y. Furukawa·D. C. Johnston
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Abstract

Single crystals of SrMn2P2 and CaMn2P2 were grown using Sn flux and characterized by single-crystal x-ray diffraction, electrical resistivity rho, heat capacity Cp, and magnetic susceptibility chi = M/H measurements versus temperature T and magnetization M versus applied magnetic field H isotherm measurements. The x-ray diffraction results show that both compounds adopt the trigonal CaAl2Si2-type structure. The rho(T) measurements demonstrate insulating ground states for both compounds. The chi(T) and Cp(T) data reveal a weak first-order antiferromagnetic (AFM) transition at the Neel temperature TN = 53(1) K for SrMn2P2 and a strong first-order AFM transition at TN = 69.8(3) K for CaMn2P2. Both compounds show an isotropic and nearly T-independent chi(T < TN). {31}P NMR measurements confirm the strong first-order transition in CaMn2P2 but show critical slowing down near TN for SrMn2P2 thus evidencing second-order character. The NMR measurements also indicate that the AFM structure of CaMn2P2 is commensurate with the lattice whereas that of SrMn2P2 is incommensurate. These first-order AFM transitions are unique among the class of trigonal (Ca, Sr, Ba)Mn2(P, As, Sb, Bi)2 compounds which otherwise exhibit second-order AFM transitions. This result presents a challenge to understand the systematics of magnetic ordering in this class of materials in which magnetically-frustrated antiferromagnetism is quasi-two-dimensional.

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N. S. Sangeetha, Santanu Pakhira, Q. -P. Ding, H. -C. Lee, V. Smetana, A. -V. Mudring, Y. Furukawa, D. C. Johnston. 2021-05-06. First-order transitions at the Neel temperatures of trigonal SrMn2P2 and CaMn2P2 single crystals containing corrugated-honeycomb Mn sublattices. https://doi.org/10.1073/pnas.2108724118

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