  We investigate the magnetic and crystal electric field (CEF) states of the
Kondo lattice system CeCuGa3 by muon spin relaxation (muSR), neutron
diffraction, and inelastic neutron scattering (INS) measurements. A
noncentrosymmetric BaNiSn3-type tetragonal crystal structure (space group I4mm)
is inferred from x-ray as well as from neutron powder diffraction. The
low-temperature magnetic susceptibility and heat capacity data show an anomaly
near 2.3 - 2.5~K associated with long range magnetic ordering, which is further
confirmed by muSR and neutron diffraction data. The neutron powder diffraction
collected at 1.7 K shows the presence of magnetic Bragg peaks indexed by an
incommensurate magnetic propagation vector k = (0.148, 0.148, 0) and the
magnetic structure is best described by a longitudinal spin density wave with
ordered moments lying in ab-plane. An analysis of the INS data based on a CEF
model reveals the presence of two magnetic excitations near 4.5 meV and 6.9
meV. The magnetic heat capacity data suggest an overall CEF splitting of 20.7
meV, however the excitation between 20 and 30 meV is very broad and weak in our
INS data, but could provide an evidence of CEF level in this energy range in
agreement with the magnetic entropy. Our analysis of INS data based on the
CEF-phonon model indicates that the two excitations at 4.5 meV and 6.9 meV have
their origin in CEF-phonon coupling (i.e. splitting of one CEF peak into two
peaks, called vibron), with an overall splitting of 28.16 meV, similar to the
case of CeCuAl3 and CeAuAl3.
