Experimental Measurement Of The Isolated Magnetic Susceptibility

The isolated susceptibility.I may be defined as a (nonthermodynamic) average over the canonical ensemble, but while it has often been discussed in the literature, it has not been clearly measured. Here, we demonstrate an unambiguous measurement of chi(I) at avoided nuclear-electronic level crossings in a dilute spin ice system, containing well-separated holmium ions. We show that chi(I) quantifies the superposition of quasiclassical spin states at these points and is a direct measure of state concurrence and populations.