Anisotropic resistivity in single crystals of the helical magnet ${\rm EuCo_{2}P_{2}}$

The anisotropic resistivity is studied in single crystals of EuCo$_{2}$P$_{2}$, a model helical antiferromagnet with $T_{\rm N} \approx 66$~K [1]. Alignment of Eu$^{2+}$ magnetic moments $(S=7/2)$ parallel to the conducting planes leads to a monotonic decrease of the in-plane resistivity, $\rho_a (T)$, on cooling due to a decrease of the magnetic spin scattering. The inter-plane resistivity, $\rho _c (T)$, with current flowing along the helix axis ($c$-axis), reveals a resistivity increase starting above $T_{\rm N}$, echoing the onset of the entropy release determined by heat capacity measurements [1]. An additional anomaly occurs in $\rho_c(T)$ at $\sim 25$~K, which may reflect an incommensurate-to-commensurate transition in the helix wave vector on cooling, since the wave vector is known to be somewhat temperature dependent [2]. \newline [1] N.~S.~Sangeetha, E.~Cuervo-Reyes, A.~Pandey, and D.~C.~Johnston, Phys. Rev. B {\bf 94}, 014442 (2016). \newline [2] M.~Reehuis, W.~Jeitschko, M.~H.~M{\"o}ller, and P.~J.~Brown, J.~Phys.~Chem.~Solids {\bf 53}, 687 (1992).