Correlation of microchemistry of cell boundary phase and interface structure to the coercivity of Sm(Co 0.784 Fe 0.100 Cu 0.088 Zr 0.028 ) 7.19 sintered magnets (Correlation of microchemistry of cell boundary phase and interface structure to the coercivity of Sm(Co0.784Fe0.100Cu0.088Zr0.028)7.19 sintered magnets)