Atomic-Scale Magnetic Properties of Truly 3d-Diluted ZnO

In search for dilute magnetic semiconductors, the magnetic properties at the atomic-scale of Fe atoms incorporated in ZnO, in a concentration range of more than five orders of magnitude from $1 × 10^{−5}$ to 2.2 at% have been probed using emission 57 Fe Mössbauer spectroscopy on implanted $^{57}Mn$ and $^{57}Co$ produced at ISOLDE/CERN. In the ultra-dilute regime ($10 ^{−5}$ at%), the system shows isolated paramagnetic $Fe^{3+}$ ions with a spin–lattice type of relaxation. At higher concentrations (between 0.02 and 0.2 at%) a transition to spin–spin type of relaxation between neighboring $Fe^{3+}$ is observed, without any signature of magnetic ordering up to 2.2 at%. Despite the many reports of dilute magnetism in 3 d -doped ZnO, this atomic level study shows no evidence of any long-range magnetic ordering between isolated Fe atoms incorporated in the ZnO lattice.