Frustrated Magnetic Cycloidal Structure and Emergent Potts Nematicity in CaMn2_2P2_2

We report neutron-diffraction results on single-crystal CaMn$_2$P$_2$ containing corrugated Mn honeycomb layers and determine its ground-state magnetic structure. The diffraction patterns consist of prominent (1/6, 1/6, $L$) reciprocal lattice unit (r.l.u.; $L$ = integer) magnetic Bragg reflections, whose temperature-dependent intensities are consistent with a first-order antiferromagnetic phase transition at the N\'eel temperature $T_{\rm N} = 70(1)$ K. Our analysis of the diffraction patterns reveals an in-plane $6\times6$ magnetic unit cell with ordered spins that in the principal-axis directions rotate by 60-degree steps between nearest neighbors on each sublattice that forms the honeycomb structure, consistent with the $P_Ac$ magnetic space group. We find that a few other magnetic subgroup symmetries ($P_A2/c$, $P_C2/m$, $P_S\bar{1}, P_C2, P_Cm, P_S1$) of the paramagnetic $P\bar{3}m11^\prime$ crystal symmetry are consistent with the observed diffraction pattern. We relate our findings to frustrated $J_1$-$J_2$-$J_3$ Heisenberg honeycomb antiferromagnets with single-ion anisotropy and the emergence of Potts nematicit

Zero-field magnetic ground state of EuMg2 Bi2

Layered trigonal EuMg2Bi2 is reported to be a topological semimetal that hosts multiple Dirac points that may be gapped or split by the onset of magnetic order. Here, we report zero-field single-crystal neutron-diffraction and bulk magnetic susceptibility measurements versus temperature χ(T) of EuMg2Bi2 that show the intraplane ordering is ferromagnetic (Eu2+,S=7/2) with the moments aligned in the ab plane while adjacent layers are aligned antiferromagnetically (i.e., A-type antiferromagnetism) below the Néel temperature

New insight into tuning magnetic phases of RMn6Sn6 kagome metals

Kagome metals with magnetic order offer the possibility of tuning topological electronic states via external control parameters such as temperature or magnetic field. ErMn$_6$Sn$_6$ (Er$166$) is a member of a group of $R166$, $R=$~rare earth, compounds hosting ferromagnetic Mn kagome nets whose magnetic moment direction and layer-to-layer magnetic correlations are strongly influenced by coupling to $R$ magnetic moments in neighboring triangular layers. Here, we use neutron diffraction and magnetization data to examine the temperature-driven transition in Er$166$ from a planar-ferrimagnetic to distorted-triple-spiral magnetic order. These data inform mean-field calculations which highlight the fragile, tunable nature of the magnetism caused by competing Mn-Mn and Mn-Er interlayer magnetic exchange couplings and Mn and Er magnetic anisotropies. This competition results in the near degeneracy of a variety of collinear, non-collinear, and non-coplanar magnetic phases which we show are readily selected and adjusted via changing temperature or magnetic field. Thermal fluctuations of the Er moment direction provide the key to this tunability.Comment: 10 pages, 7 figures, Supplementary Informatio

Frustrated magnetic cycloidal structure and emergent Potts nematicity in CaMn2 P2

We report neutron-diffraction results on single-crystal CaMn2P2 containing corrugatedMn honeycomb layers, and we determine its ground-state magnetic structure. The diffraction patterns consist of prominent (1/6,1/6,L) reciprocal-lattice unit (r.l.u.; L = integer) magnetic Bragg reflections, whose temperature-dependent intensities are consistent with a first-order antiferromagnetic phase transition at the Néel temperature TN = 70(1) K. Our analysis of the diffraction patterns reveals an in-plane 6 × 6 magnetic unit cell with ordered spins that in the principal-axis directions rotate by 60◦ steps between nearest neighbors on each sublattice that forms the honeycomb structure, consistent with the PAc magnetic space group.We find that a few other magnetic subgroup symmetries (PA2/c, PC2/m, PS¯1, PC2, PCm, PS1) of the paramagnetic P¯3m11' crystal symmetry are consistent with the observed diffraction pattern. We relate our findings to frustrated J1-J2-J3 Heisenberg honeycomb antiferromagnets with single-ion anisotropy and the emergence of Potts nematicity.This article is published as Islam, Farhan, Thaís V. Trevisan, Thomas Heitmann, Santanu Pakhira, Simon XM Riberolles, N. S. Sangeetha, David C. Johnston, Peter P. Orth, and David Vaknin. "Frustrated magnetic cycloidal structure and emergent Potts nematicity in CaMn 2 P 2." Physical Review B 107, no. 5 (2023): 054425. DOI: 10.1103/PhysRevB.107.054425. Copyright 2023 American Physical Society. Posted with permission. DOE Contract Number(s): AC02-07CH1135

Canted Antiferromagnetic phases in the layered candidate Weyl material EuMnSb2

EuMnSb2 is a candidate topological material which can be tuned towards a Weyl semimetal, but there are differing reports for its antiferromagnetic (AFM) phases. The coupling of bands dominated by pure Sb layers hosting topological fermions to Mn and Eu magnetic states provides a potential path to tune the topological properties. We present a detailed analysis of the magnetic structure on three AFM phases based on single-crystal neutron diffraction, magnetization, and heat capacity data as well as polycrystalline 151Eu Mössbauer data. The Mn magnetic sublattice orders into a C-type AFM structure below 323(1)~K with the ordered Mn magnetic moment μMn lying perpendicular to the layers. AFM ordering of the Eu sublattice occurs below 23(1)~K with the ordered Eu magnetic moment μEu canted away from the layer normal and μMn retaining its higher-temperature order. μEu is ferromagnetically aligned within each Eu layer but exhibits a complicated AFM layer stacking. Both of these higher-temperature phases are described by magnetic space group (MSG) Pn′m′a′ with the chemical and magnetic unit cells having the same dimensions. Cooling below =9(1)~K reveals a third AFM phase where μMn remains unchanged but μEu develops an additional in-plane canting. This phase has MSG P1121a′. We additionally find evidence of short-range magnetic correlations associated with the Eu between 12 K≲T≲30 K. Using the determined magnetic structures, we postulate the signs of nearest-neighbor intralayer and interlayer exchange constants and the magnetic anisotropy within a general Heisenberg-model. We then discuss implications of the various AFM states in EuMnSb2 and its topological properties.This article is published as Wilde, John M., Simon XM Riberolles, Atreyee Das, Y. Liu, T. W. Heitmann, Xiaoping Wang, Warren E. Straszheim et al. "Canted antiferromagnetic phases in the candidate layered Weyl material EuMnSb 2." Physical Review B 106, no. 2 (2022): 024420. DOI: 10.1103/PhysRevB.106.024420. Copyright 2022 American Physical Society. Posted with permission. DOE Contract Number(s): AC02-07CH11358; AC05-00OR22725