Dependence of magnetic properties and microstructure of mechanically alloyed Ni0.5Zn0.5Fe2O4 on soaking time (original) (raw)
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The separate influences of sintering temperature and soaking time on mechanically alloyed ferrites' crystallity degree and properties are reported. To understand the two influences in the case of a ferrite with the composition Ni 0.5 Zn 0.5 Fe 2 O 4 , toroids of this composition were separated into three groups for investigation of three respective and different sintering parameters. The first parameter was the sintering temperature of 500 1C to 1400 1C with a 100 1C increment. The second parameter was the sintering temperature from 800 1C to 1000 1C with a 25 1C increment which were believed the temperature range of magnetic phase transition. All toroidal samples were sintered for 10 hours in an ambient air atmosphere. The soaking time was the third parameter employed with prolonged soaking from 1 to 96 hours and a fixed sintering temperature of 800 1C. The X-ray diffraction (XRD) results of the three parameters show that the first appearance of a single phase occurred at as low as 600 1C and the intensity peaks increased as the sintering temperature and soaking time increased, yielding for the entire sintering sequence three distinct families of magnetic hysteresis loops. The density results against temperatures show almost a linear increase until 1200 1C and remain relatively unchanged for 1300 1C and 1400 1C. The increase of XRD intensity with the sintering temperature indicates higher crystallinity and possible higher values of magnetization. From the differential scanning calorimetry (DSC) result, maximum exothermic peak appear at 960 1C and the nanometer starting powders could be speculated to give high reactivity due to a high surface area. The Curie temperatures were all found to be the same i.e. 232 1C.
Journal of Superconductivity and Novel Magnetism
In this paper the effect of sintering temperature on Ni0.5Zn0.5Fe2O4 is examined closely. The evolution of toward magnetically ordered materials was to be tracked with the parallel evolving microstructure subjected to sintering temperatures in an ascending order. The starting powder of Ni0.5Zn0.5Fe2O4 was prepared via mechanical alloying and later molded into toroidal samples. After each sintering, we observed the resulting changes in the materials. The XRD data showed a single phase being formed as early as 600 °C and the peak intensity was increasing with the sintering temperature indicating an increase in the degree of crystallinity. The BH hysteresis loops showed the evolution from paramagnetism to moderate ferromagnetism to strong ferromagnetism with microstructural changes. For lower sintering temperatures, the samples showed paramagnetic behavior dominating the samples. As sintering temperature increased, paramagnetic states decreased and, at 900 °C, a moderately ferromagnetic state appeared. Sintering at 1000 °C produced a strongly ferromagnetic state giving a well-formed sigmoid-shape hysteresis loop.
Influence of the shape of the grain on the magnetization curve and the ferromagnetic hysteresis loop
Journal of Magnetism and Magnetic Materials, 1986
We have obtained theoretical expressions for the magnetization curve and hysteresis loop of polycrystalline ferrimagnets which include the effect of the shape of the grains in the sample. We obtained the expressions in terms of the ratio fl = a/c, where a and c are the semiaxes of an ellipsoid of revolution. We find a strong dependence of the area: enclosed by the hysteresis loop on the shape of the grain, i.e., on the value of ft. The slope of the initial reversible part of the magnetization curve and the magnetization curve itself also depend strongly on the value of ft.
Journal of Materials Science: Materials in Electronics, 2014
High energy ball milling and subsequent annealing were applied to synthesize nanocrystalline Ni 0.64 Zn 0.36 Fe 2 O 4 ferrite from a powder mixture of pure metal Zn, Fe 2 O 3 and NiO in an oxygen atmosphere. The structural and phase evolution of powder particles after different milling times were studied by X-ray diffractometry. The XRD results showed that a Ni-Zn ferrite was formed with some residual Fe 2 O 3 by annealing a 30-hmilled sample at as low as 400°C for 2 h. The average crystallite size of the 30 h-milled powder was estimated to be about 15 nm which grew to 21 nm after annealing at 500°C for 2 h. TEM image showed an agglomerated state of particles for 30 h-milled powders. FT-IR analysis indicated two absorption bands in the Ni-Zn ferrite structure related to octahedral and tetrahedral sites, respectively, in the range of 400-600 cm -1 . Thermogravimetric analysis showed a mass loss about 2 % for as-received powder mixture below 400°C; after that, it was almost stable. The Ni-Zn ferrite formation mechanism was detected to be in three stages: oxidation of zinc, diffusion of ZnO in Fe 2 O 3 and the formation of ZnFe 2 O 4 , and diffusion of NiO in ZnFe 2 O 4 and the formation of Ni-Zn ferrite. Vibrating sample magnetometery results revealed that a saturation magnetization of the 30 h-milled sample was about 5 emu/ g which increased to 16 emu/g after annealing at 400°C due to a reduction in density of lattice imperfections and strain.
Structural and magnetic properties of nanostructured iron oxide
Physica E-low-dimensional Systems & Nanostructures - PHYSICA E, 2011
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Materials Chemistry and Physics, 2009
Structural, surface morphological and magnetic properties of polycrystalline Ni 0.50 Zn 0.50−x−y Mg x Cr y Fe 2 O 4 (for x = 0.0, 0.1, 0.2 and y = 0.0, 0.1, 0.1) were thoroughly investigated. The lattice parameters of the samples investigated are found to decrease with increasing Mg and Cr contents. The bulk density and the average grain diameter are found to decrease with increasing Mg and Cr substitution in Ni 0.50 Zn 0.50−x−y Mg x Cr y Fe 2 O 4 for any particular sintering temperature. However, they are found to increase with increasing sintering temperatures for any individual composition. In the present investigation, the maximum bulk density and the largest average grain diameter are found for Ni 0.50 Zn 0.50 Fe 2 O 4 sintered at 1350 • C. The observed variation of lattice parameters and bulk densities of the samples investigated are explained with the help of ionic radii and atomic masses of the substituted cations. The real part of initial permeability, i , and the saturation magnetization, M s , are found to decrease with increasing Mg and Cr contents in Ni 0.50 Zn 0.50−x−y Mg x Cr y Fe 2 O 4 , whereas the Neel temperature, T N , increases. The highest i , the value of which is 432, is obtained for Ni 0.50 Zn 0.50 Fe 2 O 4 (x = 0, y = 0) composition sintered at 1350 • C with corresponding resonance frequency, f r of 2 MHz. On the other hand, the highest f r (45 MHz) is obtained for Ni 0.50 Zn 0.2 Mg 0.2 Cr 0.1 Fe 2 O 4 sintered at 1250 • C with corresponding i = 88. The relative quality factor, Q, decreases with increasing Mg and Cr contents. The highest Q values for Ni 0.50 Zn 0.50 Fe 2 O 4 and Ni 0.50 Zn 0.3 Mg 0.1 Cr 0.1 Fe 2 O 4 are observed for the samples sintered at 1250 • C. On the other hand, the highest Q value for Ni 0.50 Zn 0.2 Mg 0.2 Cr 0.1 Fe 2 O 4 is obtained for the sample sintered at 1350 • C. The observed i values and M s are related to the chemical composition, morphological nature of the grain boundaries and average grain diameters. It is also observed that increase of i is accompanied by the decrease of f r , which confirms the Snoek relation for polycrystalline ferrites.
Mn-Zn ferrite powders (Mn 0.5 Zn 0.5 Fe 2 O 4 ) were prepared by the nitrate-citrate auto-combustion method and subsequently annealed in air or argon. The effects of heat treatment temperature on crystalline phases formation, microstructure and magnetic properties of Mn-Zn ferrite were investigated by X-ray diffraction, thermogravimetric and differential thermal analysis, scanning electron microscopy and vibrating sample magnetometer. Ferrites decomposed to Fe 2 O 3 and Mn 2 O 3 after annealing above 550 1C in air, and had poor magnetic properties. However, Fe 2 O 3 and Mn 2 O 3 were dissolved after ferrites annealing above 1100 1C. Moreover, the 1200 1C annealed sample showed pure ferrite phase, larger saturation magnetization (M s =48.15 emu g À 1 ) and lower coercivity (H c = 51 Oe) compared with the auto-combusted ferrite powder (M s =44.32 emu g À 1 , H c = 70 Oe). The 600 1C air annealed sample had the largest saturation magnetization (M s = 56.37 emu g À 1 ) and the lowest coercivity (H c = 32 Oe) due to the presence of pure ferrite spinel phase, its microstructure and crystalline size.
Powder Metallurgy, 2013
In this study, nanocrystalline Ni 0?64 Zn 0?36 Fe 2 O 4 powders were prepared using a planetary ball mill. The evolution of the microstructure and magnetic properties during the milling were studied by Xray diffraction technique, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometre. It is revealed from the results of the phase analysis that nanocrystalline Ni 0?64 Zn 0?36 Fe 2 O 4 ferrite with average crystallite size of 6?18 nm and non-uniform lattice strain of 0?33% has been formed after 60 h of milling time. A progressive increase of saturation magnetisation and a dramatic decrease in coercivity were also observed with increasing milling time.