ferromagnetic, spin (cluster) glass, and paramagnetic behavior Peelamedu et al 2003 [2]. The NiFe2O4 ferrite is an inverse spinel and the ZnFe2O4 is a normal ...
MAGNETIC CHARACTERIZATION OF A NOVEL FERRITE NANOPARTICLES Z. Vakil, Anuj Jain, K.M. Gupta*, Santosh Srivastava Department of Applied Mechanics, Motilal Nehru National Institute of Technology Allahabad-211004, India Abstract Nickel doped Zinc ferrite nanoparticles with composition of NixZn1-xFe2O4 where (x=0, 0.25, 0.5, 0.75) were prepared by the chemical sol-gel process. The structure and magnetic properties were investigated by X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Vibrating sample magnetometer (VSM) respectively. The lattice parameter and crystallite size were found to decline gradually with increasing Ni content. The microstructure studies were observed by SEM analysis. The magnetic properties were characterized by the VSM, that shows the Ni0.5Zn0.5Fe2O4 has maximum saturation magnetization (61.07emu/g) and Ni0.25Zn0.25Fe2O4 with minimum Coercivity (13.02 Oe). Keywords: Nanoparticles, Ferrites, Magnetic properties, Sol-Gel Introduction Polycrystalline ferrites such as nickel zinc ferrite have a variety of applications in microwave control components such as circulators, isolators, and phase shifters Adam et al 1990[1]. Most modern soft ferrites have a spinel structure. Such structure possesses tetrahedral A-sites and octahedral B-sites in AB2O4 crystal structure. It shows vivid magnetic properties depending on their composition and cation distribution. Various cations can be placed in A-site and Bsite to tune its magnetic properties. Depending on A-site and B-site cations; it can exhibit ferromagnetic, antiferromagnetic, spin (cluster) glass, and paramagnetic behavior Peelamedu et al 2003 [2]. The NiFe2O4 ferrite is an inverse spinel and the ZnFe2O4 is a normal ferrite [3]. Ni-Zn ferrite is a mixed spinel in which tetrahedral sites are occupied by Zn2+ and Fe3+ ions, and the octahedral sites are occupied by Ni2+ and Fe3+ in the lattice [4]. The unit cell of the spinel Ni-Zn ferrite consists of the formula of the type of [ZnFe1-x]A[Ni1-xFe1+x]BO4, where A represents tetrahedral site and B represents octahedral site [5]. Other investigations [6-11] mostly consider the Ni0.5Zn0.5Fe2O4 and other compositions of Ni and Zn. In this paper we have considered the Zn1-xNixFe2O4 (where x=0.25.0.50, 0.75) and their magnetic properties to be used for making the microwave isolators. Experimentation Synthesis
Ni–Zn ferrite powders with compositions of Ni1-xZnxFe2O4 (where x = 0.25, 0.50 and 0.75) have been synthesized by sol–gel method. The process is given as in follows Fig.1.The raw materials used are analytical grade Fe(NO3)3·9H2O, Zn(NO3)2·6H2O, Ni(NO3)2·6H2O, and citric acid (C6H8O7·H2O).
Characterizations The crystalline structures of various magnetic materials have been investigated by a Wide Angle X-Ray Diffraction (WAXD), using a powder X-Ray diffractometer (PW3170 X-ray model) with Cu-K1 source at 40kv, 30mA. All the samples are recorded in the 2θ regions of 10˚- 65˚ at a scan rate of 0.02° per second. Vibrating sample magnetometer (VSM) The magnetization measurements for the prepared ferrite samples have been carried-out using a vibrating sample magnetometer (VSM) at room temperature with an applied magnetic field of 17.5 kOe. Results and Discussions The XRD patterns of all the samples Ni1-xZnxFe2O4 (where x = 0.25, 0.50 and 0.75) after the temperature treatment are shown in Fig 2 (a-c). The XRD patterns exhibit typical reflections from (220), (311), (222), (400), (422), (511), (440) planes which indicate the presence of cubic spinel structure.
Fig 2 (a) XRD of Ni0.25Zn0.75Fe2O4
Magnetization (emu/gm)
Fig 2 (b) XRD of Ni0.5Zn0.5Fe2O4
8.0E+01 6.0E+01 4.0E+01 2.0E+01 0.0E+00
-2.0E+01 -4.0E+01
-6.0E+01 -8.0E+01 -2.0E+04 -1.0E+04
0.0E+00
1.0E+04
2.0E+04
Applied field(Oe) Fig 3 (c) Hystersis curve of Ni0.75Zn0.5Fe2O4
The magnetic properties viz. saturation magnetization (Ms), remanent magnetization (M r) and coercivity (H c) are given in Table1.
Fig 2 (c) XRD of Ni0.75Zn0.25Fe2O4
Magnetization(emu/gm)
Magnetic properties The hysteresis curve of NixZn1-xFe2O4 (x = 0.25, 0.50, 0.75) nanoparticles prepared by sol gel method at room temperature are shown in Fig3(a-c). 3.00E+01 2.00E+01 1.00E+01 0.00E+00 -1.00E+01 -2.00E+01
-3.00E+01 -2.0E+04 -1.0E+04Applied 0.0E+00 1.0E+04 2.0E+04 field(Oe)
Fig 3 (a) Hysteresis curve of Ni0.25Zn0.75Fe2O4
Magnetization (emu/gm)
8.00E+01 6.00E+01 4.00E+01 2.00E+01 0.00E+00 -2.00E+01 -4.00E+01 -6.00E+01 -8.00E+01 -2.0E+04 -1.0E+04 0.0E+00
1.0E+04
Applied field (Oe)
Fig 3 (b) Hystersis curve of Ni0.50Zn0.50Fe2O4
2.0E+04
Table 1.Experimental results of Ni-Zn ferrite with different compositions
Parameters Coercive field (Oe) Saturation magnetization (emu/g) Remanent magnetization (emu/g)
x = 0.25
NixZn1-xFe2O4 x = 0.50
13.02
80.16
x= 0.75 112.58
26.97
61.07
56.77
0.9
9.92
14.1
It can be seen that the coercivity and remanent increased with increase of Ni composition, but saturation magnetization initially increases and finally decreases as shown in the Fig. 4.(a-c) respectively. Initially the Zn concentration (for Ni0.25 and Ni0.50) is effective as Zn ferrite is normal spinel, the Zn2+ ions occupy A site (tetrahedral) and transfer the Fe3+ ions to B site (Octahedral). Thus the large magnetic moment at this site increases the saturation magnetization (Ms). Ms first increases with Ni concentration and then decreases. This is due to the fluctuations in A-B and B-B interactions and spin canting. The coercivity (Hc) of Zn-ferrite increases with the doping of Ni concentration. It is because of the magneto-crystalline anisotropy constant K1, which for Ni is larger than Zn.
Conclusions The main focus of the present work is to synthesize nanomagnetic particles of NixZn1-xFe2O4 based ferrites which are suitable for high frequency applications. The compounds synthesized are Ni0.25Zn0.75Fe2O4, Ni0.5Zn0.5Fe2O4, and Ni0.75Zn0.25Fe2O4. The fine particles are characterized by X-ray diffraction technique, and VSM. The XRD reveals that the formed material has spinel structure and a single phase. It is inferred micrographs that the microstructure is affected by doping of Ni. These images confirm that both the grain size and densification are affected by an increase in concentration of doping in ferrite samples. As a result, in magnetic measurement, the absence of hysteresis area, of almost immeasurable coercivity and remanence, were observed, which is a characteristic of soft ferromagnetic material. Since Ni0.25Zn0.75Fe2O4 has minimum Remanent Magnetization (0.9 emu/g) and coercivity 13.02 Oe among all the samples it seems best to describe the characteristics of magnetic-fluid. Also the Ni0.5Zn0.5Fe2O4 has the highest saturation magnetization (61.07emu/gm), and so is most suitable for high frequency applications especially for the non-reciprocal microwave devices.
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