Magnetic and Mössbauer spectroscopic studies of NiZn ferrite nanoparticles synthesized by a combustion method

Abstract

The properties of nanocrystalline Ni 0.5 Zn 0.5 Fe 2 O 4 synthesized by an auto-combustion method have been investigated by magnetic measurements and Mössbauer spectroscopy. The as-synthesized single phase nanosized ferrite powder is annealed at different temperatures in the range 673-1,273 K to obtain nanoparticles of different sizes. The powders are characterized by powder X-ray diffraction, vibrating sample magnetometer, transmission electron microscopy and Mössbauer spectroscopy. The as-synthesized powder with average particle size of ∼9 nm is superparamagnetic. Magnetic transition temperature increases up to 665 K for the nanosized powder as compared to the transition temperature of 548 K for the bulk ferrite. This has been confirmed as due to the abnormal cation distribution, as evidenced from room temperature Mössbauer spectroscopic studies.

Structural, magnetic and Mössbauer spectral studies of nanocrystalline Ni0.5Zn0.5Fe2O4 ferrite powders

“…It appears from the recent literature survey in an assembly of single domain NiZn ferrite nanoparticles that even though the particles do not show superparamagnetic behavior in external magnetic field, fluctuations of magnetization along easy axis of magnetization is possible [10,11,27]. In the present study the sample G3 having the size ∼24 nm exhibit hysteresis at room temperature whereas slow relaxation of the magnetization vector about easy axis of magnetization has been reported in the Mössbauer spectrum of the sample.…”

“…The Curie temperature of sample G1 is 573 K. Interestingly, the Curie temperatures of all these samples are larger than the reported value of 563 K for bulk materials [3]. Though, an increase in T C up to 665 K is reported earlier [27], a change in the Curie temperature to 833 K, as high as 270 K for G4 has never been observed so far. It is known that in the Ni 1−x Zn x Fe 2 O 4 series, the T C value is highest for x = 0, i.e.…”

“…7 and 8. Mössbauer spectra of G1 indicate [11,[26][27][28]36,37]. The superparamagnetic doublets in the Mössbauer spectrum account 67% of the relative spectral areas corresponding to Fe 3+ ions of tetrahedral (A) and octahedral (B) sites.…”

“…Though these changes have been explained in terms of finite size scaling, it was later explained in terms of the changes in the distribution of cations in the two different sites of the ferrite lattice, because from finite size scaling effects a decrease in the Curie temperature from that of the bulk is expected [29][30][31][32]. Such enhancement in Curie temperature is also observed for nanosized NiFe 2 O 4 and Ni 0.5 Zn 0.5 Fe 2 O 4 [26,27].…”

“…Studies on various aspects of nanocrystalline ferrites, synthesized by different wet chemical methods, have been reported in the literature [9,[21][22][23][24][25][26][27][28]. For MnFe 2 O 4 , an increase in the Curie temperature as high as 97 K, when compared with that of the bulk material is reported, when the particle size is reduced to 7.5 nm [9].…”