Magnetic transition in highly frustrated ${\mathrm{SrCr}}_8$${\mathrm{Ga}}_4$${\mathrm{O}}_{19}$: The archetypal kagome´ system

Both dc and ac magnetic susceptibility have been carefully measured and analyzed in order to determine the features of the low-temperature magnetic state of the highly frustrated ${\mathrm{SrCr}}_8$ ${\mathrm{Ga}}_4$ ${\mathrm{O}}_{19}$ compound. The scaling analysis of the nonlinear part of the dc magnetic susceptibility gives clues that indicate that the nature of the magnetic state below ${\mathit{T}}_{\mathit{f}}$ does not correspond to a conventional spin glass. This idea is further confirmed by the study of the dynamic scaling that also differs from what is expected for a conventional spin glass. A progressive change towards a more conventional magnetic ordering below ${\mathit{T}}_{\mathit{f}}$ is observed by substituting Ga atoms by Fe atoms in the compound ${\mathrm{SrCr}}_8$ ${\mathrm{Ga}}_{4\mathrm{-}2\mathit{x}}$ ${\mathrm{Fe}}_{\mathit{x}}$ ${\mathrm{O}}_{19}$. For x=1.5, both the scaling analysis of the nonlinear part of the dc magnetic susceptibility and the dynamic scaling seem to indicate that a true spin-glass phase transition does exist at ${\mathit{T}}_{\mathit{f}}$. This change in the magnetic behavior is attributed to the fact that the presence of a magnetic atom in the 4${\mathit{f}}_{\mathrm{VI}}$ sites as a first neighbor of the Cr atoms, located in the 12k sites, will impose a ‘‘local preferential direction’’ for the magnetic moments removing somehow the strong intrinsic magnetic frustration of the kagomé lattice.