Insights into the evolution from ferromagnetism to antiferromagnetism: A doping-dependent study of ${\mathrm{NaCrSi}}_x{\mathrm{Ge}}_{2-x}{\mathrm{O}}_6(0\le x\le 2)$

Journal Article · 01 February 2019 · Physical Review B

DOI: https://doi.org/10.1103/PhysRevB.99.064427 · OSTI ID:1495957

Tian, Wei  ^[1]; Yan, Jiaqiang  ^[2]; Kolesnikov, Alexander I.  ^[1]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Division
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science & Technology Division

NaCrGe₂O₆ and NaCrSi₂O₆ are isostructural compounds exhibiting different magnetic ground states. NaCrGe2O6 adopts a ferromagnetic ground state with Tc=6K, whereas NaCrSi₂O₆ orders antiferromagnetically below T_N=3.4K. Although it has been proposed that the intriguing magnetic behavior in Cr-based pyroxenes involves competition between antiferromagnetic direct exchange and ferromagnetic superexchange interactions, a delicate balance that is sensitive to Cr-Cr distance and local distortion, no spectroscopy study has been done to determine the microscopic interactions in these compounds. To delve deeper into the evolution from ferromagnetism to antiferromagnetism, we performed a doping-dependent study to investigate how the substitution of Ge by Si affects the magnetic properties of NaCrSi_xGe_2-xO₆ (x=0, 0.5, 1, 1.5, 2). Neutron diffraction and magnetization measurements show that replacing larger Ge with smaller Si simultaneously suppresses the ferromagnetic order. The lattice constants and the unit-cell volume contract, i.e., chemical pressure effect, and the Cr-Cr distance within the chain gradually decreases with increasing Si doping. High-resolution inelastic neutron-scattering studies of the spin waves of NaCrGe₂O₆ and NaCrSi₂O₆ indicate that replacing Ge with Si has profound effect on the intrachain coupling, whereas it has negligible effect on the interchain couplings. We compare our results, which indicate NaCrGe₂O₆ is magnetic quasi-one-dimensional (1D) and NaCrSi₂O₆ is three-dimensional (3D), with LiCr(Si,Ge)₂O₆, where LiCrSi₂O₆ is proposed to be magnetic quasi-1D and LiCrGe₂O₆ is 3D, and discuss the different behaviors in magnetic dimensionality crossover in the context of how substituting Ge with Si fine-tunes the relative ratio between the intrachain and interchain couplings that defines the magnetic dimensionality in these materials.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1495957
• Alternate ID(s): OSTI ID: 1495235
• Journal Information: Physical Review B, Vol. 99, Issue 6; ISSN 2469-9950
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English