Magnetic phase diagram of RFe$_4$Al$_8$ (R$=$Dy,Gd,Lu) single crystals

Single crystals of RFe$_4$Al$_8$ (R$=$Dy,Gd,Lu) were grown using self-flux at high temperatures $T$ and investigated by magnetization, electrical transport, and x-ray measurements. Crystals grow typically in form of long needles ($\| [001]$) with facets $\bot [110]$ and good crystallinity. Iron moments order below $T_N \approx 175\,{\rm K}$ (R$=$Dy), $150\,{\rm K}$ (R$=$Gd) and $195\,{\rm K}$ (R$=$Lu). Measurements on LuFe$_4$Al$_8$ indicate that fields $H$ up to $7\,{\rm T}$ do not noticeably shift $T_N$. There is no clear signature of Dy moment ordering at lower $T$, in zero field. However, there is evidence of a metamagnetic transition (likely first order) to a low $T$ high $H$ ($\bot[001]$) ferrimagnetic phase, attributed to Dy ordering. Gd moments order via a first order transition at about $30\,{\rm K} $ ($H=0$). The transition is shifted to lower $T$ by applying $H\|[001]$ (to zero temperature in about $1\,{\rm T}$). The resistivity along $[001]$ jumps to a higher value below the transition. The $H-T$ phase diagrams as well as the need for the microscopic determination of the magnetic structure will be discussed.