The spin-reversal in dilute Li2β(Li1βxβFexβ)N with x<1 % is
dominated by resonant quantum tunneling of spatially well-separated states. We
report on the effect of finite couplings between those states that give rise to
cooperative, simultaneous quantum tunneling of two spins. This phenomenon,
known as spin-spin cross relaxation, effectively elucidates the fine-structure
observed in isothermal magnetization loops, a previously unresolved aspect.
Temperature and field-dependent magnetization measurements were conducted over
a range from T = 2 K to 300 K in applied fields of up to ΞΌ0βH = 7 T.
Magnetic dipole fields are computed numerically. Our findings affirm the
absence of stoichiometric defects in Li2β(Li1βxβFexβ)N and underscore
its exemplary suitability as a model system for investigating spin-reversal
processes at the microscopic level. This is attributed to its comparatively
simple crystal structure, the availability of large single crystals, elevated
characteristic energies, and well-defined energy levelsComment: 7 pages, 4 figure