Elastic and Inelastic neutron scattering results in heavily Cu doped NaFe$_{1-x}$Cu$_x$As with x approaching 0.5

Compared to Co and Ni doping, doping Cu in NaFe$_{1-x}$Cu$_x$As causes the system to become insulating at high dopings. We found in heavily Cu doped NaFe1-xCuxAs, low energy spin excitations are strongly enhanced similar to Cu doped Fe(Se,Te). We have further found for x approaching 0.5, Fe and Cu tend to order and results in a novel magnetic state, explaining the enhanced low energy spin excitations in heavily Cu doped NaFe$_{1-x}$Cu$_x$As.