Magnetostriction of single-crystal La2CuO4

Longitudinal magnetostriction (Δl/l) experiments have been used to probe the magnetic phase diagram of single-crystal La2CuO4 at 4.2, 77, 145, and 191 K. The geometry used is (l∥H∥b̂), where b̂ is a unit vector along the orthorhombic b axis, perpendicular to the CuO2 planes. The observed magnetic transition is associated with an induced alignment, along the field direction, of the small out-of-plane canting of the Cu2+ spins. At all temperatures, the transition is marked by a small increase in l, with Δl/l about 2 to 3×10-8. A large hysteresis was observed at 4.2 K, with the transition field, Ht, in the up trace being 60.1 kOe, and in the down trace 45.8 kOe. This hysteresis strongly decreases with increasing temperature. At 191 K the jump in l is still quite sharp indicating that the transition is still first order. Our values of Ht are in good agreement with those obtained on similar crystals using different techniques