Abstract
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 TN=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 NaCrSixGe2-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.
| Original language | English |
|---|---|
| Article number | 064427 |
| Journal | Physical Review B |
| Volume | 99 |
| Issue number | 6 |
| DOIs | |
| State | Published - Feb 20 2019 |
Funding
The neutron-scattering research at the High Flux Isotope Reactor and Spallation Neutron Source, Oak Ridge National Laboratory, was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. J.Q.Y. is supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. ORNL is managed by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The U.S. Government retains, and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for U.S. Government purposes.