We report precision measurements of the nuclear magnetic moment of textsuperscript{43}Catextsuperscript{+}, made by microwave spectroscopy of the 4s $^2$S$_{1/2}$ $left|F=4, M=0rightrangle rightarrow left|F=3, M=1rightrangle$ ground level hyperfine clock transition at a magnetic field of $approx$ 146 G, using a single laser-cooled ion in a Paul trap. We measure a clock transition frequency of $f = 3199941076.920 pm 0.046$ Hz, from which we determine $mu_I / mu_{rm{N}} = -1.315350(9)(1)$, where the uncertainty (9) arises from uncertainty in the hyperfine $A$ constant, and the (1) arises from the uncertainty in our measurement. This measurement is not corrected for diamagnetic shielding due to the bound electrons. We make a second measurement which is less precise but agrees with the first. We use our $mu_I$ value, in combination with previous NMR results, to extract the change in shielding constant of calcium ions due to solvation in D$_2$O: $Delta sigma = -0.00022(1)$.
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