https://doi.org/10.1007/s100510050029
Study of the positive muon Knight shift in UNi2Al3: Evidence for a tetravalent U4+-state and crystalline electric field splitting
1
Institute for Particle Physics of ETHZ, 5232 Villigen
PSI, Switzerland
2
Physics Department, Graduate School of Science, Tohoku University,
Sendai 980-8578, Japan
3
Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
Received:
20
April
1999
Published online: 15 January 2000
We report on transverse field (TF) Muon Spin Rotation (μSR) measurements
on a single crystal of the hexagonal heavy fermion superconductor
UNi2Al3 between 5 K and 300 K. From the measured muon Knight
shift (KS) in the easy (a,b)-plane and along the c-axis we extracted
the local magnetic susceptibility tensor
,
which arises from the nearest U-neighbors. By comparison with the bulk
susceptibility
it is found that
and
agree
well above 150 K but deviate considerably in the basal plane below 150 K, due
to the disturbance introduced by the
. We succeed in reproducing both
and
on the basis of a crystalline electric field (CEF)-approach assuming U to be
in the tetravalent
state. The disturbance introduced by the
affects the CEF-Hamiltonian in an
expected manner, suggesting strongly that a CEF-picture implying a rather
local 5f-electron wave function is indeed valid. Reanalyzing older data on
UPd2Al3 we arrive at the same conclusion. A necessary condition for
extracting the local susceptibility was the knowledge of the
-site,
this information was derived from the analysis of the TF-relaxation rates.
At low temperatures we found about 30%
of the implanted
at the d-site and none at this site above 200 K. The
majority fraction was found to be in a tunneling state over
six m (or k)-sites
around the b-site. No long range diffusion was seen up to room temperature.
PACS: 76.60.Cq – Chemical and Knight shifts / 71.70.Ch – Crystal and ligand fields / 76.75.+i – Muon spin rotation and relaxation
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2000