Copper nano-crystalline CuFe 2 O 4 powder was prepared by a coprecipitation method from iron chloride and copper chloride in the presence of octanoic acid (C 8 H 16 O 2) as the surfactant. The samples prepared were characterised by XRD, TEM, SEM, FT-IR and VSM. SEM and TEM indicated that the particles were quasi spherical with particle sizes in the range of 23 ± 7 nm. The magnetic properties of the sample were measured using a vibration sample magnetometer (VSM), which showed that the sample showed typical ferromagnetic behaviour at room temperature, while the finite coercivity present was 245.5 Oe at 300 K.
Nano-crystalline ferrites are materials of considerable interest because of their unique dielectric, magnetic and optical properties, which makes them attractive both from a scientific and a technological point of view (Abdullah Dar et al., 1998). These magnetic materials are the basis of a very active field of research due to the new phenomena that take place at the nano-scale level as a result of the interaction of quantum, finite, surface and inter facial effects. Spinel ferrite nano-particles with a high surface area have many technical applications in various fields such as high density information storage, ferrofluids, catalysts, drug selection, hyperthermia, magnetic separation and magnetic resonance imaging (Cannas et al., 2010) . The key questions in these systems are how these nano-structures modify their magnetic and electronic properties and how one can take advantage of those new features to improve applications. Consequently, the understanding and control of the effects of nano-structures on the properties of particles have become increasingly relevant topics for technological applications (Batlle et al., 2011).
The study of the magnetic behaviour of ferrites has attracted considerable attention in recent decades, particularly since deviations in mass behaviour have been widely reported for particle sizes below a range of approximately 100 nm. This is due to the finite-size effects and the increasing fraction of atoms located on the surface with less atomic coordination than in the nucleus as the particle size decreases, resulting in a significant decrease in the magnetisation of the particles ( Batlle et al., 2011). Surface spin disturbance due to surface symmetry breaking leads to a smaller saturation magnetisation, high field differential susceptibility, extremely high closing fields and hysteresis loops displaced after field cooling of the sample together With vitreous behaviour. This has been explained in terms of the existence of a surface layer of disordered turns that freeze in a state similar to that of spinning glass due to magnetic frustration, producing both an exchange field acting on the ordered nucleus and an increase of The anisotropy of the particles. The most obvious and highly studied finite-size effect is super para-magnetism. The basic principle is that the magnetic anisotropic energy that holds a magnetised particle in a particular direction is generally proportional to the volume of the particle. Therefore, below a critical size at room temperature, the thermal fluctuations are sufficient to rotate the magnetisation of the particles, thus demagnetising a set of said particles. Although it is a well studied effect, it is understood only at a phenomenological level.
Recently, considerable attention has been paid to ferrites of different morphology and their size and shape-dependent properties, as well as their corresponding applications. Both physical and chemical methods have been developed for the synthesis of ferrite nano structures of different morphologies. Chemical methods have advantages over the physical, such as low cost, reaction takes place at low temperature, and the possibility of large-scale production. It is widely appreciated that the cationic distribution in spinel ferrites on which many physical and chemical properties depend is a complex function of the processing parameters and depends on the material preparation method (Sepelak et al., 2007). Selecting an appropriate method is the key factor in obtaining high quality ferrites. Various processing methods have been developed to obtain nano-crystalline ferrites such as hydro-thermal synthesis, chemical coprecipitation, polymer precursor techniques, sol-gel, shock wave, spray drying, sleep-chemical process and mechanical alloy (Sivakumar et al. , Kotnala et al., 2010). It is well known that different routes produce different micro-structures and crystal sizes. Therefore, based on ease and reproducibility, the chemical coprecipitation method is widely used, but leads to the precipitation of nano-crystals with a relatively large size distribution (Zhang et al., 1998). In the present study, a reverse micro-emulsion technique for the synthesis of nano-crystals has been selected. Reverse micelles, which are essentially aqueous nano-dimensional droplets that exist in micro-emulsions with certain compositions, are known to present an excellent means for the synthesis of nano-particles. The particles produced by this method are generally very thin, mono-disperse, morphologically controlled and highly crystalline compared to the other processes (Li and Park 1999, Yener and Giesche 2001). The current interest in synthesising nano-structured nickel-zinc ferrite particles is due to their low coercivity, high resistivity and high saturation magnetisation similar to that of magnetite (Thakur et al., 2007). In this work, we have reported on the synthesis of the nano-sized crystalline mixed ferrite system, namely Ni0.7Zn0.3Fe2O4, by chemical coprecipitation and reverse micro-emulsion method. The analysis of structure and morphology was performed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The magnetic properties of the synthesised samples were measured using a sample vibration magnetometer at different temperatures and discussed in detail.