Mn-Zn ferrites

Magnetic materials—control of oxygen composition and physical properties of Mn-Zn ferrites... 

Magnetic materials can be classified into two groups metal and alloy materials, and metal oxide materials represented by ferrites. We here describe the Mn-Zn ferrites, which are used, for example, as the magnetic heads in magnetic recording, focusing on the preparative processes and physical properties, which are closely related to the oxygen non-stoichiometry. 

First, we discuss the phase relation from the viewpoint of the phase rule. Because Mn- Zn ferrite is composed of four elements (Mn, Zn, Fe, O), the freedom F in the phase rule is expressed as f = 6 — p. Considering one solid phase with a spinel structure (see Section 2.5 and Ref. 3), equilibrated with the oxygen (partial) pressure Po., we get the relation F = 4. The starting compounds for the preparation of Mn-Zn ferrite are ZnO, MnO, and Fe2O3, in the molar ratio a / 3 — (a -I- j6). This mixture is heated at fixed temperature and partial oxygen pressure, and the product obtained has the composition Zn Mn Fcj Under conditions of fixed temperature, fixed oxygen... 

In order to use Mn Zn ferrites as magnetic head materials, the materials have to show the following characteristics ... 

The thus obtained high-density Mn-Zn ferrite was investigated in detail from the view of physical and mechanical properties, that is, the relationships between the composition of metals (a,) ) and <5 the magnetic properties such as temperature and frequency dependence of initial permeability, magnetic hysteresis loss and disaccommodation and the mechanical properties such as modulus of elasticity, hardness, strength, and workability. Figures 3.13(a) and (b) show the optical micrographs of the samples prepared by the processes depicted in Fig. 3.12(a) and (b), respectively. The density of the sample shown in Fig. 3.13(a) reached up to 99.8 per cent of the theoretical value, whereas the sample shown in Fig. 3.13(b) which was prepared without a densification process, has many voids. 

Previously, polycrystalline Mn-Zn ferrite had been prepared by solid state reaction in vacuo or by hot-press methods. Using these methods densification and the size of grains could be controlled, but control of the 5 value was a problem. Tanaka succeeded in preparing high performance Mn-Zn ferrites by controlling Poz-... 

T. Tanaka, Study on high-dense Mn-Zn Ferrite prepared by controlling the oxygen non-stoichiometry. Thesis, Keio University, 1981. 

A1203 matrix [38], nanoscale FeOOH particles [39], dispersed ultrafine Mn-Zn ferrite particles [40], polydispersed ferrite particles in a magnetic fluid [41], Fe-based nanoparticles in a polyethylene matrix [42], a granular Cu-Co alloy [43] and maghemite (/-Fe203) nanoparticles in ferrofluids [32], No... 

Most spinel ferrites used in device applications are not simple ternary oxides but rather contain proprietary mixtures of several different magnetic ions tailor made for specific applications. So-called (Mn, Zn) ferrites of general formula Zn+ c Fe+ i-x[Mn+ i cF ]04 and related (Ni, Zn) ferrites... 

Haba et al. [28] have computed the temperature distributions induced by pulsed irradiation of Mn-Zn ferrite with a copper vapor laser (k = 511 and 578 nm) under the processing conditions of Table 18.1. This particular source is characterized by a top hat, circular intensity distribution. 

Mn-Zn ferrites have been prepared by calcination at 900 °C of spray-dried particles (Jain, Das Avtar, 1976). The solution was prepared by mixing sulphates. The formation of the Mn-Zn ferrite involved decomposition of the FeS04 to a-FejOj, which reacted with the ZnSQ to form Zn ferrite. MnS04 decomposed last to react with the Zn ferrite leading to the desired Mn-Zn ferrite. 

Broussaud, D., Aboudaf, M., Perriat, P. Rolland, J. L. (1989). Oxidation state/green strength relationships in Mn-Zn ferrite. In Advances in Ferrites Proceedings of the Fifth International Conference on Ferrites, India, 1989,... 

Slick, P. I. (1971). A thermogravimetric study of the equilibrium relations between a Mn-Zn ferrite and an Oj-Nj atmosphere. In Ferrites Proceedings of the International Conference, July 1970, Japan. Eds. Y. Hoshino, S. lida and M. Sugimoto. University of Tokyo Press, Tokyo, pp. 81-3. 

Yan, M. F. Johnson, D. W. (1978). Impurity-induced exaggerated grain growth in Mn-Zn ferrites. Journal of the American Ceramic Society, 61,342-9. 

Fig. 4.61. Domain wall velocity as a function of applied field for a Mn-Zn ferrite single crystal at 77 K. (Adapted from Dillon Earl, 1959.)...

In polycrystalline ferrites, grain boundaries can also have an influence on eddy-current losses. In high-permeability Mn-Zn ferrites, for instance, CaO and SiOj are used as additives to decrease the Fe content and increase the grain boundary resistivity (Berger et ai, 1989), both processes limiting eddy-current losses. 

Beer, A. Schwarz, J. (1966). New results on the influence of filter stipulations on the qualities of Mn, Zn ferrites. IEEE Transactions on Magnetics, 2,470-4.. 

Hard-disc drive heads are subjected to a heavier use and therefore need a different design in order to prevent wear and extend the useful life of both the disc and the head. Hard-disc drive heads (also known as Winchester heads) make no physical contact with the hard disc. They are designed to fly very close to the disc, supported by the air flow resulting from the disc rotation. Fig. 5.18. The magnetic element in Winchester heads is usually a Mn-Zn ferrite. 

Discuss for Mg2Ti04 and Mn-Zn ferrite, which is preferred, normal or inverse spinel, on the basis of Pauling s rules. 

Example 5 GBs in magnetic ferrites affect the initial permeability, p. The permeability of Mn-Zn ferrite increases from about 0.8 x 10 up to 3.5 x 10 when the grain size is increased from 5 pm to 15 pm (Chapter 33). Although porosity has a role, it has been determined that grain size is more important. 

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