Spin relaxation measurements [#!OseroffJAP94!#,#!BrillPRL94!#,#!ItohPRB95!#]

Oseroff et al. measured the EPR signal from Cu²⁺ ions, and found a decrease of signal intensity below $T_{\rm SP}$ [155]. Brill et al. performed high-field ESR measurements and identified singlet-triplet and triplet-triplet transitions [156]. Itoh et al. performed ^63,65Cu-NMR and NQR measurements [157], and found a drop of the ⁶³Cu nuclear T₁ relaxation rate below $T_{\rm SP}$.