Two-Dimensional Spin Dynamics in the Itinerant Ferromagnet LaCoPO Revealed by Magnetization and 31P-NMR Measurements

We have performed magnetization and ³¹P-NMR measurements on the itinerant ferromagnet LaCoPO (Curie temperature TCurie~ 44 K) with a layered structure in order to investigate spin dynamics in the paramagnetic state. The linear scaling between the Knight shift K at the P site and the bulk susceptibility χ above TCurie indicates that the P nucleus is suitable for investigating magnetic properties. The temperature and magnetic field dependences of the nuclear spin-lattice relaxation rate divided by the temperature 1/T₁T at the P site show characteristic features of itinerant ferromagnets, such as ZrZn₂ and Y(Co₁₋ₓAlₓ)₂. In addition, the relationship between 1/T₁T and χ above TCurie suggests that ferromagnetic fluctuations possess a two-dimensional (2D) characteristic. The present data show that LaCoPO is a unique ferromagnet, where the 2D fluctuations anticipated from the crystal structure are predominant down to almost TCurie.