Magnetic Behavior of the 2-Leg and 3-Leg Spin Ladder Cuprates Srn-1Cun+1O2n

We have performed muon spin relaxation measurements of the spin-ladder cuprates Srn-1Cun+1O2n ( n=3,5). The 3-leg ladder system ( n=5) shows static magnetic order at T∼52 K, which is between the ordering temperatures of the one-dimensional chain system Sr2CuO3 ( TN∼5 K) and of the two-dimensional layer system Ca0.86Sr0.14CuO2 ( TN∼540 K). The 2-leg ladder system ( n=3) does not show any magnetic order down to 20 mK, in agreement with the theoretical prediction of a nonmagnetic ground state with a spin gap for even-leg-number ladder systems.