Hard-magnetic material

C. A. M. van den Broek, Proceedings of the IrdEuropean Conference on Hard Magnetic Materials, Bond Materialen Kennis, Amsterdam, 1973, p. 53. 

G. S. Krijtenburg, Proceedings of the 1 stEuropean Conference on Hard Magnetic Materials, Vienna (unpublished), 1966. 

Table 10. Properties of Permanent (Hard) Magnet Materials ...

Fig. 9. Progress in energy product for hard magnetic materials. To convert to cal, divide by 4.184.

Fig. 10. Demagnetization curves of hard magnetic materials A, Nd2Fe B B, Sm(Co, Cu,Fe,Zr)2 C, SmCo D, bonded SmCo E, Alnico 5 F, Mn—Al—C G, Alnico 8 H, Cr—Co—Fe I, ferrite , bonded ferrite. To convert T to G, multiply by 10". ...

A good design for a hard magnetic material is to have small, elongated particles. 

Important is the use of light rare earth elonents for production of hard magnetic materials. Most prominent are alloys of samarium with cobalt in the atomic ratio 1 5 or 2 17. It may also be assumed that in further development of these materials on a larger scale that praseodymium, neodymium, lanthanum and also individual heavy rare ecu h elements will be used to achieve particular effects. Interesting is the development of magnetic bubble memories based on gadolinium-galliiimrgarnets. 

Figure 6.55 Comparison of hysteresis loops for soft and hard magnetic materials. From K. M. Ralls, T. H. Courtney, and J. Wulff, Introduction to Materials Science and Engineering. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission John Wiley Sons, Inc.

Coehoom, R., 1990, in Proceedings of the NATO-ASI "Supermagnets, Hard Magnetic Materials , eds... 

For quite a few years we have been concerned with the use of molecular systems in memory devices. Whatever the final objective might be, a fundamental requirement for the system is to have an hysteresis effect with regard to a given perturbation. When it is so, a transition between two electronic states takes place for a certain value of the perturbation, /Vf, when the perturbation increases, and for another value of the perturbation, Pcl, when the perturbation decreases, with Pc[ < Pcf. Between those two critical values, the state of the system depends on its history or on the information which has been stored. It is of course well known that a hard magnetic material might be used for storing information. Our work provides evidence of the possibility that molecular chemistry might provide compounds of that kind. 

Hard magnetic materials these materials cannot be magnetized nor demagnetized easily (fig. 11.5.5b). Examples of such materials are Alnico alloys containing iron, alloys of rare earths and Fe-Cr-Co alloys. 

A hard magnetic material has a much greater hysteresis than a soft magnetic material. The differences are much greater than shown in this figure. 

Some of the best hard magnetic materials are those with a hexagonal structure. In these there are only two possible domains, differing by 180°. Table 18.5 lists the maximum BH product for several alloys. Cheap permanent magnets can be made by aligning fine iron powder in a magnetic field while it is being bonded by rubber or a polymer. 

There are four different classes of hard magnetic materials ... 

Much higher temperatures are achievable for SmCo5 and other highly anisotropic materials. However, typical hard-magnetic materials have temperature-dependent anisotropies that are maximized at or above room temperature [16, 77]. Little work has been done to optimize anisotropies at low temperatures, although it is known that some compounds with Tc < 300 K have huge anisotropies of 100 to 1000 MJ/m3 [83, 208],... 

In the section 2 of this chapter, an introduction is given to the main concepts required for the understanding of coercivity in hard magnetic materials. The various types of hard nanostructures and the procedures used for their preparation are described in section 3. The specific properties of hard nanostructure magnetism are described in section 4. In section 5, the properties of industrial materials are presented and some applications are briefly summarised. 

In usual hard magnetic materials, thermal activation effects are the source of a coercive field decrease by typically 10% at room temperature. Importantly, they provide an experimental access to the critical volume for reversal, which may be identified with the activation volume, vact. 

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