4 research outputs found
The double life of electrons in magnetic iron pnictides, as revealed by NMR
We present a phenomenological, two-fluid approach to understanding the
magnetic excitations in Fe pnictides, in which a paramagnetic fluid with
gapless, incoherent particle-hole excitations coexists with an
antiferromagnetic fluid with gapped, coherent spin wave excitations. We show
that this two-fluid phenomenology provides an excellent quantitative
description of NMR data for magnetic "122" pnictides, and argue that it finds a
natural justification in LSDA and spin density wave calculations. We further
use this phenomenology to estimate the maximum renormalisation of the ordered
moment that can follow from low-energy spin fluctuations in Fe pnictides. We
find that this is too small to account for the discrepancy between ab intio
calculations and neutron scattering measurements.Comment: Accepted for publication in Europhys. Lett. 6 pages, 4 figure
Putative spin-nematic phase in BaCdVO(PO)
We report neutron scattering and AC magnetic susceptibility measurements of
the 2D spin-1/2 frustrated magnet BaCdVO(PO). At temperatures well
below , we show that only 34 % of the spin moment orders
in an up-up-down-down strip structure. Dominant magnetic diffuse scattering and
comparison to published sr measurements indicates that the remaining 66 %
is fluctuating. This demonstrates the presence of strong frustration,
associated with competing ferromagnetic and antiferromagnetic interactions, and
points to a subtle ordering mechanism driven by magnon interactions. On
applying magnetic field, we find that at K the magnetic order vanishes
at 3.8 T, whereas magnetic saturation is reached only above 4.5 T. We argue
that the putative high-field phase is a realization of the long-sought
bond-spin-nematic state