ИСТИНА

Here we present an extended study of Co-doped alkaline earth hydroxyapatites revealing their high magnetic anisotropy and SMM-like properties. The results support that the Co ion confined in the apatite structure behaves like a mononuclear SMM, or single-ion magnet (SIM). This is connected to very high magnetic anisotropy of the alone paramagnetic [OCoO] group formed in the trigonal channel. The separation between Co-ions is above 6.8 Å which is large enough to suppress possible inter-ion interactions. On the decrease of the Co concentration, the slow relaxation behaviour persists, exhibiting even longer relaxation time  at the lowest temperatures as a rule. Two Co-based SIM atomic groups are distinguished, to which different magnetization relaxation behaviour is attributed: “normal” slow relaxation (NSR) emerging in a small magnetic field and very slow relaxation (VSR) occurring also in the zero magnetic field. The NSR centres are characterized by the magnetization reversal energy barrier Ueff of 50-60 cm-1 while the VSR centres have several times higher Ueff ranging from ca. 200 cm-1 for strontium apatites to 387 cm-1 for barium apatites.