  The one-body tunnel picture of single-molecule magnets (SMMs) is not always
sufficient to explain the measured tunnel transitions. An improvement to the
picture is proposed by including also two-body tunnel transitions such as
spin-spin cross-relaxation (SSCR) which are mediated by dipolar and weak
superexchange interactions between molecules. A Mn4 SMM is used as a model
system. At certain external fields, SSCRs lead to additional quantum resonances
which show up in hysteresis loop measurements as well defined steps.
