Dynamic Proton Polarization in AlK and Al(NH4) Alum

Abstract

Over 50% proton polarization has been attained in three sulfate alum crystals containing dilute ${\mathrm{Cr}}^{3+}$ ions, at 1 K and ∼19.5 kG, with limited microwave power (∼¼ W). The EPR spectra are dominated by the (-½, ½) transition, with linewidths varying from 10 to 22 G. Al(N${\mathrm{H}}_4$) alum should make useful polarized proton targets because it contains 1.97 times as much hydrogen by weight as lanthanum magnesium nitrate.