4.4 Summary

From the $\mu$SR measurements of the spin-ladder material Sr_n-1Cu_n+1O_2n, we observed static magnetic order for the 3-leg ladder system at T$\sim$52 K, while, in the 2-leg ladder system, no magnetic order was present down to 20 mK. Our results support the theoretical expectations of the magnetic ground states of the ladder systems, namely, a non-magnetic ground state for the 2-leg ladder system, and a magnetic ordered state for the 3-leg ladder system.