We report 35Cl NMR, ESR, μSR and specific heat measurements on the
S=1/2 frustrated kagom\'e magnet kapellasite,
α−Cu3​Zn(OH)6​Cl2​, where a gapless spin liquid phase is
stabilized by a set of competing exchange interactions. Our measurements
confirm the ferromagnetic character of the nearest-neighbour exchange
interaction J1​ and give an energy scale for the competing interactions ∣J∣∼10 K. The study of the temperature-dependent ESR lineshift reveals a
moderate symmetric exchange anisotropy term D, with ∣D/J∣∼3%. These
findings validate a posteriori the use of the J1​−J2​−Jd​ Heisenberg
model to describe the magnetic properties of kapellasite [Bernu et al., Phys.
Rev. B 87, 155107 (2013)]. We further confirm that the main deviation from this
model is the severe random depletion of the magnetic kagom\'e lattice by 27%,
due to Cu/Zn site mixing, and specifically address the effect of this disorder
by 35Cl NMR, performed on an oriented polycrystalline sample.
Surprisingly, while being very sensitive to local structural deformations, our
NMR measurements demonstrate that the system remains homogeneous with a unique
spin susceptibility at high temperature, despite a variety of magnetic
environments. Unconventional spin dynamics is further revealed by NMR and
μSR in the low-T, correlated, spin liquid regime, where a broad
distribution of spin-lattice relaxation times is observed. We ascribe this to
the presence of local low-energy modes.Comment: 15 pages, 11 figures. To appear in Phys. Rev.