Magnetostriction of single-crystal La2CuO4.

Abstract

Longitudinal magnetostriction ($\frac{\ensuremath{\Delta}l}{l}$) experiments have been used to probe the magnetic phase diagram of single-crystal ${\mathrm{La}}_{2}$Cu${\mathrm{O}}_{4}$ at 4.2, 77, 145, and 191 K. The geometry used is ($l\ensuremath{\parallel}\mathrm{H}\ensuremath{\parallel}\stackrel{^}{\mathrm{b}}$), where $\stackrel{\mathrm{^}}{\mathrm{b}}$ is a unit vector along the orthorhombic $b$ axis, perpendicular to the Cu${\mathrm{O}}_{2}$ planes. The observed magnetic transition is associated with an induced alignment, along the field direction, of the small out-of-plane canting of the ${\mathrm{Cu}}^{2+}$ spins. At all temperatures, the transition is marked by a small increase in $l$, with $\frac{\ensuremath{\Delta}l}{l}$ about 2 to 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$. A large hysteresis was observed at 4.2 K, with the transition field, ${H}_{t}$, 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 ${H}_{t}$ are in good agreement with those obtained on similar crystals using different techniques.