At a magnetic field determined by the zero crossing of the ω12 frequency of a paramagnetic species like a muonium-substituted radical some muons experience a total magnetic field of zero, simply because the hyperfine field exactly cancels the externally applied field. Since the muon polarization does not rotate under this condition, an integral positron asymmetry is seen even in transverse field if the resonance condition is met. Essentially, the same data acquisition set-up and high beam currents as used in other integral μSR techniques, such as ALCR, can be used to scan for the resonant field, which scales linearly with the hyperfine constant, Aμ. A theoretical treatment of the resonances in the case of isotropic Aμ is presented along with measured spectra demonstrating the technique.
