Spin canting and surface spin disorder in Ni substituted Co-Cd ferrite nanoparticles synthesized by fuel deficient combustion method.

Abstract The nanocrystalline Cd 0.5-X Ni X Co 0.5 Fe 2 O 4 (x = 0.0 to 0.5) ferrites were synthesized by auto combustion technique using hexamine as fuel. The substitution of non magnetic Cd2+ ions in the tetrahedral site causes canting on the octahedral site. The saturation magnetization increases with Ni substitution up to X = 0.3 and then decreases with further increase in Ni substitution at room temperature. This behaviour is consistent with Yafet–Kittel magnetic ordering. A three sub-lattices model (A, B 1 and B 2) has been used to describe the magnetic behaviour of the ferrites. Low temperature unsaturated magnetization behaviour indicates the core shell structure of the nanoparticles i:e ordered core spins and randomly oriented surface spins. Reduced remanent magnetization values (Mr/Ms) suggest that the samples have uniaxial anisotropy at room temperature. The variation of magnetizations of the samples with temperature was studied by ZFC–FC technique at three different applied fields of 250 Oe, 500 Oe and 1000 Oe. The nature of the curves showed a change with increase in Ni concentration. The blocking temperature and anisotropy increased with Ni concentration. The average crystallite size was found to be in the range of 6–13 nm. The lattice constant decreased with Ni concentration. The Dielectric property has been explained on the basis of Maxwell-Wagner's two layer model while A.C. susceptibility studies indicate single domain-superparamagnetic domain structure. The Curie temperature shifts to higher temperature with increase in Ni concentration. Highlights • Fuel deficient hexamine to metal nitrates ratio. • Spin canting with increase in Cd concentration. • Change in the shapes of the MT curves with Ni substitution. • Uniaxial anisotropy at room temperature. • Core-shell spin model of magnetization. [ABSTRACT FROM AUTHOR]