Electron spin dynamics in grain-aligned LaCoPO: An itinerant ferromagnet

Abstract

$^{139}\text{L}\text{a}$ NMR study was performed in grain-aligned $(\stackrel{P\vec}{c}\ensuremath{\parallel}\stackrel{P\vec}{{H}_{0}})$ sample of LaCoPO and polycrystalline LaFePO. Knight shift is isotropic and temperature independent in LaFePO. It is strongly temperature dependent and anisotropic in LaCoPO. The spin-lattice relaxation rate in LaCoPO clearly reveals the existence of three-dimensional spin fluctuations both in the paramagnetic and ferromagnetic state over and above the dominant two-dimensional spin fluctuations in the paramagnetic state, observed earlier from $^{31}\text{P}$ NMR measurements in the same oriented sample [M. Majumder, K. Ghoshray, A. Ghoshray, B. Bandyopadhyay, B. Pahari, and S. Banerjee, Phys. Rev. B 80, 212402 (2009)]. The spin fluctuation parameters in LaCoPO determined from $^{139}\text{L}\text{a}$ NMR relaxation and magnetization data, using the self-consistent renormalization theory, are in close agreement and follow the universal Rhodes-Wohlfarth curve.