Magnetic and Electrical Properties of System Cualxfe_2-Xo₄ Ferrite

The most important ferrimagnetic materials are certain double oxides of iron and another metal, called ferrites. These materials are extensively used in many applications such telecommunication, audio and video, power transformers and many other applications involving electrical signals normally not exceeding a few megacycles for seconds, magnetic fluids, microwave absorbers and medical diagnostics [1]. Diamagnetic substitution in single and mixed ferrites have received a lot of attention over the past years. The preference of non magnetic ions in spinels is found to alter their magnetic and electrical properties, and studies have revealed useful information on the nature of the exchange interaction, direction of magnetization, cation distribution, spin canting etc. [2].

The most important ferrimagnetic materials are certain double oxides of iron and another metal, called ferrites. These materials are extensively used in many applications such telecommunication, audio and video, power transformers and many other applications involving electrical signals normally not exceeding a few megacycles for seconds, magnetic fluids, microwave absorbers and medical diagnostics [1]. Diamagnetic substitution in single and mixed ferrites have received a lot of attention over the past years. The preference of non magnetic ions in spinels is found to alter their magnetic and electrical properties, and studies have revealed useful information on the nature of the exchange interaction, direction of magnetization, cation distribution, spin canting etc. [2].

Figure 1 & 2

Figure 1: X-ray diffraction patterns of CuAlxFe_2-xO₄.

Figure 2: Temperature dependence of electrical conductivity of CuAlxFe_2-xO₄.

Astronomers know of three sources of redshift/blueshift: Doppler shifts; gravitational redshifts (due to light exiting a gravitational field); and cosmological expansion (where space itself stretches). This article concerns itself only with Doppler shifts.

Note that the third source here is ‘cosmological expansion’ which is the fantasy with no conformation beyond the early Doppler. Once the transfer in figure 2 B is understood, the redshift is much more likely to come from the rotation of the sky relative to us as observers. The picture in figure 1 is also redshift that denies motion away. The idea of motion away becomes ‘circular’ reasoning and may have never existed.

The second source here is the always ignored gravitational redshift which overrides the idea of a constant speed c. The exit from a gravitational field results in a slowing of the speed, thus red shift.

The first source here is Doppler shifts. As shown Doppler gives various impressions of the motion of the source that must be resolved. A Doppler redshift can arrive from various relative motions of stars. So, we can choose to accept that ‘the sky of all-stars’ is in circular motion around earth. (or any other central body one chooses). That circular motion adds some redshift to the light sent by all stars.

XRD patterns of all the compositions presented on Figure 1 revealed are crystallizing in a FCC structure (space group Fd3m). The resistivity of the sample decreases with increasing temperature. Linearity shown on Ahrrenius plot on Figure 2 indicates that the transport occurs with constant activation energy. The electrical resistivity increases with the content of aluminum, due to its conductive property. The results showed that the maximum saturation magnetization was obtained in CFO while compared to the other samples in the series. The increase in aluminum content results in a significant decrease in saturation magnetization and remanence while the coercivity increases.

The authors are grateful to the Brazilian agencies, CNPq and FAPEMIG.

1. MI Rosales, AM Plata, ME Nicho, A Brito, MA Ponce, et al. (1995) Effect of sintering conditions on microstructure and magnetic properties of Mn-Zn ferrites, Journal of Materials Science 30: 4446-4450.
2. BS Trivedi, NN Jani, HH Joshi, RG Kulkarni (1995) Cation distribution of the system CuAlxFe₂–xO₄ by X-rays and Mossbauer studies. Journal of Materials Science 35: 5523-5526.