Serious discrepancies between nuclear magnetic resonance and neutron scattering measurements in the critical region of classic two-dimensional magnets and anomalous behaviors at low temperatures

A characterization of 2D critical behavior in the classic 2D antiferromagnets K2NiF4, Rb2MnF4, and K2MnF4 made originally by Birgeneau et al. [Phys. Rev. B 1, 2211 (1970)], using neutron scattering (NS), is used to review NMR data in these compounds and in some classic 2D ferromagnets. On analyzing the NMR data, very serious discrepancies were found between the NMR and NS results for the critical exponent ß, with the values of the NMR ßs being some 50% higher. Some novel results were also found, including 2D cases where ß = 0.33 (but characterized by a non-3D parameter, D~1). The discrepancies surely need to be resolved, and if the present analysis of the NMR data is further validated, these results could present a clear and nontrivial hurdle for current critical-region theories. Additionally, from the NMR data it was found that the lowtemperature behaviors of these classical 2D systems are at odds with the predictions of conventional spinwave theory analyses. Disciplines Physical Sciences and Mathematics | Physics Comments Suggested Citation: Bykovetz, N., Klein, J. and Lin, C.L. (2007). Serious discrepancies between nuclear magnetic resonance and neutron scattering measurements in the critical region of classic two-dimensional magnets and anomalous behaviors at low temperatures. Journal of Applied Physics. 109, 07E119. © 2007 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics and may be found at http://dx.doi.org/10.1063/1.3549596. This journal article is available at ScholarlyCommons: http://repository.upenn.edu/physics_papers/136 Serious discrepancies between nuclear magnetic resonance and neutron scattering measurements in the critical region of classic two-dimensional magnets and anomalous behaviors at low temperatures N. Bykovetz, J. Klein, and C. L. Lin Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396, USA (Presented 16 November 2010; received 1 October 2010; accepted 14 November 2010; published online 25 March 2011) A characterization of 2D critical behavior in the classic 2D antiferromagnets K2NiF4, Rb2MnF4, and K2MnF4 made originally by Birgeneau et al. [Phys. Rev. B 1, 2211 (1970)], using neutron scattering (NS), is used to review NMR data in these compounds and in some classic 2D ferromagnets. On analyzing the NMR data, very serious discrepancies were found between the NMR and NS results for the critical exponent b, with the values of the NMR bs being some 50% higher. Some novel results were also found, including 2D cases where b1⁄4 0:33 (but characterized by a non-3D parameter, D 1). The discrepancies surely need to be resolved, and if the present analysis of the NMR data is further validated, these results could present a clear and nontrivial hurdle for current critical-region theories. Additionally, from the NMR data it was found that the low-temperature behaviors of these classical 2D systems are at odds with the predictions of conventional spin-wave theory analyses. VC 2011 American Institute of Physics. [doi:10.1063/1.3549596]