Magnetic phase diagram of the spin-Peierls compoundCuGeO3doped with Al and Sn

Abstract

The magnetic phase diagram of the doped inorganic spin-Peierls compound ${\mathrm{CuGe}}_{1\ensuremath{-}x}{Y}_{x}{\mathrm{O}}_{3}$ ($Y=\mathrm{Sn}$ or Al) is studied in magnetic fields up to $B\ensuremath{\sim}50 \mathrm{T}$ at temperatures 0.32--20 K. The comparative analysis of the magnetization data and the resonant magnetoabsorption spectra for the frequency range 20--120 GHz shows that the spin-Peierls phase is not destroyed up to ${x}_{\mathrm{Sn}}=0.01$ and ${x}_{\mathrm{Al}}=0.02.$ The strong effects of doping on the magnetic phase transition between the spin-Peierls (D) and the incommensurate (M) phases are observed. The temperature dependence of the transition field ${B}_{\mathrm{DM}}(T)$ demonstrates a nonmonotonous behavior with a maximum at $T\ensuremath{\sim}9 \mathrm{K}.$ Doping by Sn and Al reduces the amplitude of the ${B}_{\mathrm{DM}}(T)$ maximum by a factor of 2 with respect to the undoped crystal. The magnetic hysteresis width $\ensuremath{\Delta}B(T)$ at $T<1 \mathrm{K}$ increases substantially in both the Al- and Sn-doped crystals. The magnitude \ensuremath{\chi} of the magnetic transition along the phase boundary ${B}_{\mathrm{DM}}(T)$ follows a critical behavior similar to that of the superlattice peak: $\ensuremath{\chi}={\ensuremath{\chi}}_{0}[1\ensuremath{-}{(T/T}^{*}){]}^{\ensuremath{\beta}},$ where ${T}^{*}\ensuremath{\approx}12 \mathrm{K}$ is the temperature of the triple point and $\ensuremath{\beta}=0.75\ifmmode\pm\else\textpm\fi{}0.04.$ A model of the magnetic hysteresis in the spin-Peierls compounds based on a universal scaling of the magnetic phase diagram and g-factor renormalization in the transition region $B\ensuremath{\sim}{B}_{\mathrm{DM}}$ is suggested. The influence of disorder on the properties of the ${\mathrm{CuGeO}}_{3}$ crystals is discussed.