We report $^{ 75}$As NMR studies on single crystals of rare-earth doped iron pnictides superconductor Ca$_{ 1-x}$Pr$_{ x}$Fe$_{ 2}$As$_{ 2}$ ($x$=0.075 and 0.15). The $^{ 75}$As spectra show a chemical pressure effect with doping and a first order structure transition to the collapsed tetragonal phase upon cooling. A sharp drop of the Knight shift is seen below the structural transition, whereas $1/T_1$ is strongly enhanced at low-temperatures. These evidences indicate quenching of Fe local magnetism and short-range ordering of Pr$^{ 3+}$ moment in the collapsed tetragonal phase. The quenched Fe moment through structure collapse suggests a strong interplay of structure and magnetism, which is important for understanding the nature of the collapsed tetragonal phase.
Categories: cond-mat.supr-con