Elastic anomalies induced by spin-flop in La_1.88Sr_0.12CuO₄

Temperature dependence of the velocity V_s and the attenuation of the ultrasonic waves are measured to investigate the relation between the spin type of magnetic order and lattice instability of the low-temperature tetragonal phase in La_2-xSr_xCuO₄ (x ∼ 1/8). In the field above 8 T along the [0 1 0]_o direction of the orthorhombic notation, a significant increase of V_s in the c₄₄ mode is observed below ∼15 K where spin-flop occurs. This gigantic increase of V_s suggests that the structural transformation from the orthorhombic to the low-temperature tetragonal phase is induced by the spin-flop.