Mössbauer spectroscopy of spin dynamics in Mn_xFe_1-xSe_0.85 superconductors: Evidence for an incommensurate-spin-density-wave state

H. H. Hamdeh¹, M. M. El-Tabey¹, R. Asmatulu², J. C. Ho¹, T. W. Huang³, K. W. Yeh³ and M. K. Wu³

¹  Department of Physics, Wichita State University - Wichita, KS 67260, USA
²  Mechanical Engineering, Wichita State University - Wichita, KS 67260, USA
³  Institute of Physics, Academic Sinica - Taipei, Taiwan

Corresponding author: hussein.hamdeh@wichita.edu

Received: 23 October 2009
Accepted: 18 March 2010

Abstract

In the tetragonal crystalline structure of Mn_xFe_1-xSe_0.85, the magnetic state contains low- and high-spin Fe²⁺, with high-spin numbers equal to that of the combined Mn substitute and Se deficiency atoms. The state is pinned by “spin-hopping” around substitution centers via high-spin low-spin conversions. During the structural distortion from tetragonal to orthorhombic, from 90 K to 70 K, the rate of spin conversions increases and the iterant character of the magnetic state is enhanced. In the orthorhombic structure, the spin dynamics evolve into an incommensurate spin-density wave (ISDW). Excitations of the ISDW decrease with temperature and level out across the superconducting phase. The ISDW appears to have more than one oscillation mode and contributions from high-order harmonics.