Temperature Dependent Magnetic Properties of Samarium Substituted Nanocrystalline Nickel Ferrite for Biomedical Applications
Sanjeet Kumar Paswan1#, Subhadeep Datta2, Murli Kumar Manglam2, Shampa Guha2, Manoranjan Kar2, Lawrence Kumar1
1 - Department of Nanoscience and Technology, Central University of Jharkhand Ranchi, Brambe -835205 India
2 - Department of Physics, Indian Institute of Technology Patna, Bihta-801106 India
Abstract: Spinel ferrite nanoparticles having general formula MFe2O4 (M=divalent metal ion, e.g. Co, Cu, Ni, etc.) have attracted wide attention in recent years for understanding fundamental nanomagnetism and their technological applications in diverse fields. Among the family of spinel ferrite nanoparticles, nickel ferrite (NiFe2O4) is a soft magnetic material which crystallizes to mixed spinel structure. It is a centrosymmetric ferrimagnetic material whose magnetic ordering temperature is far above than room temperature ~ 858 K. It exhibits low coercivity, moderate saturation magnetization, high resistivity, excellent chemical, thermal and structural stability at room temperature. The magnetic behaviour in this material is primarily governed by the spin coupling of the unpaired 3d electrons of nickel and iron cations present at the tetrahedral (A) and octahedral (B) sites. The magnetic properties of nickel ferrites nanoparticle can be tuned strongly by varying its size. However, it is difficult to tune the size of the particle in a controlled way as the size is affected by the rate of the nucleation and its subsequent growth. One could control the size of the particle by restricting its rate of nucleation and subsequent growth with introducing a large strain at the lattice site by incorporating suitable substituent element. Substituting very small amount of rare earth cations into the spinel lattice is expected to distort the crystal structure by lowering the symmetry. It may induce a high strain at the lattice site due to the large difference in their ionic radius. As an effect, it would restrict the growth of the particle which results in tunable properties. In addition to this, one can expect an appearance of spin coupling of 3d-4f electrons which will modify the overall magnetic properties.In the present work; we report the experimental study on the temperature dependence of magnetic properties of uniaxial Sm3+ substituted NiFe2O4 nanoparticles. The Sm3+ substituted nickel ferrite sample with empirical formula NiFe2-xSmxO4 (x=0.0 and 0.06) have been synthesized using the standard citrate precursor method. Single-phase Sm3+ substituted nanocrystalline nickel ferrite samples have been observed by analyzing the XRD pattern by employing the Rietveld refinement technique despite being a large difference in ionic radius of Sm3+ and Fe3+cations. The pure nickel ferrites are observed in the bulk phase. The size of the particle of Sm3+ substituted samples is in the range of 24-34 nm as estimated from SEM micrograph. The dc magnetic hysteresis loop measurements have been carried out within the temperature range 60-400K using a vibrating sample magnetometer (VSM) over a field range of ± 3T. The investigated sample exhibit narrow hysteresis loop and low coercivity at each temperature indicating that it belongs to the family of soft ferrite. The magnetocrystalline anisotropy constant (K1) and saturation magnetization (Ms) have been determined from the hysteresis loops using the law of approach to saturation (LAS) model. The fitting to LAS yields the anisotropy constant of the order of ~ 105 erg/cm3. The presence of spontaneous magnetization at every fixed temperature has been investigated by the Arrott plot method which shows a strong convex curvature with finite spontaneous magnetization revealing the ferromagnetic character of samples. The difference in Ms value has been observed obtained by LAS model and Arrott plot method which may be ascribed to strain factor.The saturation magnetization decreases (Ms) with increasing temperature and it has been analyzed using modified Bloch’s equation (MBE). The fitting of MBE to Ms vs T plot of substituted samples yields the parameters Ms(O) ~ 46.31, B~10-6 and Tc~812K where Ms(O) is the saturation magnetization as T tends to zero, B is the Bloch constant and Tc is the Curie transition temperature. The coercive field increases monotonically with decreasing temperature which has been fitted well to Kneller’s law. The fitting yields the parameter Hc(O)~ 395 and TB~ 315 K where Hc(O) is the coercive field as T approaches to zero and TB is the mean blocking temperature.Zero field- cooling (ZFC) and field-cooling (FC) curves have been measured at an applied magnetic field of 100 Oe from 60 to 400K using VSM. Field cooling (FC) curve shows the trend of gradual increase with decreasing temperature indicates the lower strength of interparticle interaction. The mean blocking temperature estimated from the plot of derivative of the difference between FC and ZFC magnetization with respect to temperature lies around 320 K which is close to the value obtained by Kneller’s law.The ZFC and FC curve does not coincide even at 400 K indicating the existence of large ferrite particles and broad particle size distribution which is well supported by SEM micrograph. By comparing the ZFC-FC data and hysteresis curve it reveals that the value of coercivity and remanence values of the sample at room temperature is very low indicating the superparamagnetic tendency and it is expected to approach superparamagnetic limit above room temperature. The Squareness ratio of the substituted sample is within the range of 0.1-0.3 which confirms the assembly of single-domain particles with uniaxial anisotropy. Due to low coercivity and remanence, the present sample can be easily guided by external magnetic fields. The above properties are desirable for biomedical application such as magnetic separation technique, molecular detection, therapeutic agent in hyperthermia, a targeted drug delivery carrier as well as contrast agents in magnetic resonance imaging.
Keywords: Coercivity; Magnetic anisotropy; Superparamagnetic; Saturation magnetization; Blocking temperature;
References: 1. Bhowmik et al. J. Magn. Magn.Mater. 460 (2108) 177-187.
2. Chatterjee et al. J. Appl. Phys. 116 (2014) 153904-8
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