Investigations of magnetic excitations in a La2CuO4 single crystal

A detailed neutron scattering study is carried out of magnetic excitations in pure La₂CuO₄ in the low energy region up to 15 meV, at temperatures in the vicinity of the transition temperatureT _N to the paramagnetic state. In particular the question of existence of propagating spin waves in this energy region is addressed. The experimental results show that the energy region studied (up to 15 meV) is characterized by aquasielastic peak of the width of order 4 meV (at 300 K). Thus the magnetic correlation function has relaxational behavior in the studied energy region, no indications for propagating spin waves are obtained. The measured quasielastic width agrees well with existing theories. Polarized neutrons and polarization analysis are also used to identify the magnetic origin of the observed scattering.