Magnetic penetration depth of κ-(BEDT-TTF)2Cu[N(CN)2]Br, determined from the reversible magnetization

We present results of the dc magnetization of single-crystalline κ-(BEDT-TTF${)}_2$Cu[N(CN${)}_2$]Br. From the slope of the linear M(lnH) dependence of the reversible magnetization, the magnetic penetration depth λ(T) is estimated. At low temperatures, λ(T) shows only a weak T dependence, consistent with conventional pairing. For the in-plane London penetration depth we find ${\lambda }_{\mathit{L}}$(0)=(650±20) nm. Small deviations from a pure BCS behavior indicate some tendency towards intermediate or strong-coupling and/or a somewhat reduced carrier mean free path.