Noncentrosymmetric Triangular Magnet CaMnTeO₆: Strong Quantum Fluctuations and Role of s⁰ versus s² Electronic States in Competing Exchange Interactions

Abstract

Noncentrosymmetric triangular magnets offer a unique platform for realizing strong quantum fluctuations. However, designing these quantum materials remains an open challenge attributable to a knowledge gap in the tunability of competing exchange interactions at the atomic level. Here, we create a new noncentrosymmetric triangular S = 3/2 magnet CaMnTeO6 based on careful chemical and physical considerations. The model material displays competing magnetic interactions and features nonlinear optical responses with the capability of generating coherent photons. The incommensurate magnetic ground state of CaMnTeO6 with an unusually large spin rotation angle of 127°(1) indicates that the anisotropic interlayer exchange is strong and competing with the isotropic interlayer Heisenberg interaction. The moment of 1.39(1) μB, extracted from low‐temperature heat capacity and neutron diffraction measurements, is only 46% of the expected value of the static moment 3 μB. This reduction indicates the presence of strong quantum fluctuations in the half‐integer spin S = 3/2 CaMnTeO6 magnet, which is rare. By comparing the spin‐polarized band structure, chemical bonding, and physical properties of AMnTeO6 (A = Ca, Sr, Pb), we demonstrate how quantum‐chemical interpretation can illuminate insights into the fundamentals of magnetic exchange interactions, providing a powerful tool for modulating spin dynamics with atomically precise control.This article is protected by copyright. All rights reserved

ISODISTROTLaMTeO6 (M = Ga3+ and Mn3+): the critical role of electronic configuration and cation ordering in crystal structures

“…This magnetic frustration release should be attributed to the Mn 3+ ( d 4 ) Jahn–Teller distortion-induced monoclinic structural distortion, which creates three nonequivalent nearest-neighbour Mn 3+ –O–Te 6+ –O–Mn 3+ superexchange pathways. More importantly, most isostructural LaFeTeO 6 ( P 3̄1 c ) 15 and AMn(IV)TeO 6 ( P 312 or P 6̄2 m ) 1,2,17 compounds exhibit characteristic low-dimensional magnetic behavior with a subtle magnetic transition peak, in stark contrast to the sharp AFM transition peak observed for LaMnTeO 6 , probably ascribed to its higher structural symmetry-induced stronger magnetic frustration.…”

“…Recently, PbSb 2 O 6 -type oxides have attracted extensive attention due to their flexible and quasi-two-dimensional crystal structure-induced appealing functional properties, such as quantum fluctuations and second harmonic generation (SHG). 1–4 The quasi-two-dimensional trigonal structure ( P 3̄1 m ) of PbSb 2 O 6 is built by alternating honeycomb-like [Sb 2 O 6 ] 2− anionic layers and triangular Pb 2+ cationic layers. Such a layered structure can be maintained by a family of isoelectronic oxides with the general formula AM 2 O 6 , where A-cations can be Ba 2+ , Pb 2+ , Sr 2+ , Ca 2+ , Hg 2+ , Cd 2+ , Ni 2+ , Mn 2+ , and Co 2+ , and M-cations can be As 5+ and Ru 5+ .…”

“…15,16 In contrast, completely M-site-ordered compositions adopt a polar P 312- or P 6̄2 m -structure (M = Al 3+ , Ga 3+ , Ge 4+ , and Mn 4+ ) with the same lattice matrix as the archetype PbSb 2 O 6 -structure and thus give rise to promising SHG properties. 1–4,17 Such a cationic ordering-driven inversion symmetry breaking has been used as a promising strategy for designing new noncentrosymmetric oxides with other classic structure types, such as garnet- and CaTa 2 O 6 -type structures. 18,19 Moreover, Poeppelmeier et al proposed that the electronic effect of M-cations plays a decisive role in the AMTeO 6 type of structure, that is, AMTeO 6 favours a polar structure when M is a main group cation like Al 3+ , Ga 3+ , and Ge 4+ .…”

“…4 However, the Mn 4+ -based series AMnTeO 6 (A = Ba 2+ , Sr 2+ , Ca 2+ , and Pb 2+ ) is an exception and adopts a chiral P 312-structure. 1,2,17…”