Magnetic properties of Sr0.95Nd0.05Fe12-xScxO19 hexaferrite nanocrystals: (T, H, x) phase diagram

Abstract Recently conical magnetic order induced by Sc3+ doping has been reported in ferrimagnetic M-type hexagonal ferrite single- and polycrystals resulting in multiferroic properties of spin origin in bulk material. We were interested in Sc-induced modifications of superexchange interactions in M-hexaferrite nanocrystals since a reduction in size is usually accompanied by degradation in properties important for applications. Nd-stabilized, Sc-doped M-type strontium hexaferrite nanocrystalline powder was obtained by citric sol-gel method. Crystal- and microstructure of Sr0.95Nd0.05Fe12-xScxO19 (x = 0.60, 0.84, 1.08 1.56) were controlled by X-ray diffraction and scanning electron microscopy. Temperature variation in magnetic hysteresis loops and temperature dependences of magnetization in zero field cooling-field heating experiments were measured from 10 K to 300 K in various magnetic fields. The analysis shows a conical magnetic ordering at low temperatures, below Tcone and enabled us to construct the (Tcone, H, x) phase diagram. Though the effect is similar to that induced by selectively substituted Sc3+ in the place of ferric ions at the 4f2 and 12k Wyckoff positions in the hexagonal lattice of single and polycrystals the temperatures Tcone in nanocrystalline, single domain particles are considerably lower.