The Magnetic Spin Ladder (C_{5}H_{12}N)_{2}CuBr_{4}: High Field Magnetization and Scaling Near Quantum Criticality

Abstract

The magnetization, $M(H\le 30$ T, 0.7 K $\le T\le 300$ K), from single crystals and powder samples of (C${}_5$H${}_{12}$N)${}_2$CuBr${}_4$ has been used to identify this system as an $S=1/2$ Heisenberg two-leg ladder in the strong coupling limit, $J_{\perp }=13.3$ K and $J_{\parallel }=3.8$ K, with $H_{c1}=6.6$ T and $H_{c2}=14.6$ T. An inflection point in $M(H,T=0.7$ K) at half-saturation, $M_s/2$, is described by an effective \emph{XXZ} chain. The data exhibit universal scaling behavior in the vicinity of $H_{c1}$ and $H_{c2}$, indicating the system is near a quantum critical point.

4 pages, 4 figures