31 research outputs found
Magneto-structural coupling and harmonic lattice dynamics in CaFeAs probed by M\"ossbauer spectroscopy
In this paper we present detailed M\"ossbauer spectroscopy study of
structural and magnetic properties of the undoped parent compound
CaFeAs single crystal. By fitting the temperature dependence of the
hyperfine magnetic field we show that the magneto-structural phase transition
is clearly first-order in nature and we also deduced the compressibility of our
sample to be . Within the Landau's theory of phase
transition, we further argue that the observed phase transition may stem from
the strong magneto-structural coupling effect. Temperature dependence of the
Lamb-M\"ossbauer factor show that the paramagnetic phase and the
antiferromagnetic phase exhibit similar lattice dynamics in high frequency
modes with very close Debye temperatures, 270\,K.Comment: 6 pages,5 figures Accepted by J. Phys.: Condens. Matte
A M\"ossbauer study of the magneto-structural coupling effect in SrFeAs and SrFeAsF
In the present paper, we report a comparison study of SrFeAs and
SrFeAsF using M\"ossbauer spectroscopy. The temperature dependence of the
magnetic hyperfine field is fitted with a modified Bean-Rodbell model. The
results give much smaller magnetic moment and magneto-structural coupling
effect for SrFeAsF, which may be understood as due to different inter-layer
properties of the two compounds.Comment: 4 pages, 2 figures,conference ICAME2011, to be appear in Hyperfine
Interaction
BaFe12O19 single-particle-chain nanofibers : preparation, characterization, formation principle, and magnetization reversal mechanism
BaFe12O19 single-particle-chain
nanofibers have been successfully prepared by
an electrospinning method and calcination
process, and their morphology, chemistry,
and crystal structure have been characterized
at the nanoscale. It is found that individual
BaFe12O19 nanofibers consist of single nanoparticles which are found to stack along the
nanofiber axis. The chemical analysis shows that the atomic ratio of Ba/Fe is 1:12, suggesting a
BaFe12O19 composition. The crystal structure of the BaFe12O19 single-particle-chain nanofibers
is proved to be M-type hexagonal. The single crystallites on each BaFe12O19 single-particlechain
nanofibers have random orientations. A formation mechanism is proposed based on
thermogravimetry/differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and transmission
electron microscopy (TEM) at six temperatures, 250, 400, 500, 600, 650, and 800 �C.
The magnetic measurement of the BaFe12O19 single-particle-chain nanofibers reveals that the
coercivity reaches a maximum of 5943 Oe and the saturated magnetization is 71.5 emu/g at
room temperature. Theoretical analysis at the micromagnetism level is adapted to describe the
magnetic behavior of the BaFe12O19 single-particle-chain nanofibers