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

Abstract

The nanocrystalline Cd sub(0.5-X) Ni sub(X) Co sub(0.5) Fe sub(2) O sub(4) (x = 0.0 to 0.5) ferrites were synthesized by auto combustion technique using hexamine as fuel. The substitution of non magnetic Cd sup(2+) 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 sub(1) and B sub(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.