  Measurements of low temperature transport and thermodynamic properties have
been used to characterize the non-Fermi liquid state of the itinerant
ferromagnet ZrZn$_2$. We observe a $T^{5/3}$ temperature dependence of the
electrical resistivity at zero field, which becomes $T^2$ like in an applied
field of 9 T. In zero field we also measured the thermal conductivity, and we
see a novel linear in $T$ dependence of the difference between the thermal and
electrical resistivities. Heat capacity measurements, also at zero field,
reveal an upturn in the electronic contribution at low temperatures when the
phonon term is subtracted. Taken together, we argue that these properties are
consistent with a marginal Fermi liquid state which is predicted by a
mean-field model of enhanced spin fluctuations on the border of ferromagnetism
in three dimensions. We compare our data to quantitative predictions and
establish this model as a compelling theoretical framework for understanding
ZrZn$_2$.

Strongly Correlated Electrons