323 research outputs found
Large magnetoresistance in the antiferromagnetic semi-metal NdSb
There has been considerable interest in topological semi-metals that exhibit
extreme magnetoresistance (XMR). These have included materials lacking
inversion symmetry such as TaAs, as well Dirac semi-metals such as Cd3As2.
However, it was reported recently that LaSb and LaBi also exhibit XMR, even
though the rock-salt structure of these materials has inversion symmetry, and
the band-structure calculations do not show a Dirac dispersion in the bulk.
Here, we present magnetoresistance and specific heat measurements on NdSb,
which is isostructural with LaSb. NdSb has an antiferromagnetic groundstate,
and in analogy with the lanthanum monopnictides, is expected to be a
topologically non-trivial semi-metal. We show that NdSb has an XMR of 10^4 %,
even within the AFM state, illustrating that XMR can occur independently of the
absence of time reversal symmetry breaking in zero magnetic field. The
persistence of XMR in a magnetic system offers promise of new functionality
when combining topological matter with electronic correlations. We also find
that in an applied magnetic field below the Neel temperature there is a first
order transition, consistent with evidence from previous neutron scattering
work.Comment: 5 pages, 6 figure
Viscosity measurements on Ionic liquids : a cautionary tale
The vibrating-wire viscometer has proven to be an exceedingly effective
means of determining the viscosity of liquids over a wide range of temperature and
pressure. The instrument has a long history but a variety of technological and theoretical
developments over a number of years have improved its precision and most
recently have enabled absolute measurements of high accuracy. However, the nature
of the electrical measurements required for the technique has inhibited its widespread
use for electrically conducting liquids so that there have been only a limited number
of measurements. In the particular context of ionic liquids, which have themselves
attracted considerable attention, this is unfortunate because it has meant that one primary
measurement technique has seldom been employed for studies of their viscosity.
In the last 2 years systematic efforts have been made to explore the applicability of
the vibrating-wire technique by examining a number of liquids of increasing electrical
conductivity. These extensions have been successful. However, in the process we have
had cause to review previous studies of the viscosity and density of the same liquids
at moderate temperatures and pressures and significant evidence has been accumulated
to cause concern about the application of a range of viscometric techniques to
these particular fluids. Because the situation is reminiscent of that encountered for
a new set of environmentally friendly refrigerants at the end of the last decade, in
this paper the experimental methods employed with these liquids have been reviewed
which leads to recommendations for the handling of these materials that may have consequences beyond viscometric measurements. In the process new viscosity and
density data for 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide
[C6mim][NTf2], 1-ethyl-3-methylimidazolium ethyl sulfate [C2mim][EtSO4], and
1-ethyl-3-methylpyridinium ethyl sulfate [C2mpy][EtSO4] have been obtained
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