Magnetisation

When a complex magnetisation mode is desired, isotropic materials are preferred. Lateral magnetisation, always in multipole, is only appHed to isotropic materials. 

Fig. 10. Aligning—magnetising modes where represents aligning direction and (---------) the neutral sones. (a) Segment, radially aligned, diametrically...

Fig. 7. Thermomagnetic recording, (a) A focused laser beam generates a thermal profile in the magnetic layer, (b) The coercive force in the layer is reduced and its magnetisation can be reversed by a small magnetic field, here 30 kA/m. At room temperature, the coercive force is high and the written domains are...

Fig. 12. Temperature dependences of the magnetisation one curve typical for ferrimagnetic films, eg, RE-TM or garnets, the other one typical for ferromagnetic Co/Pt multilayers (39). compensation temperature = Curie temperature.

Figure 2 shows the two hysteresis loops for a medium and a head material. The coercivity, the saturation magnetisation, Af or iaduction, B, remanent magnetisation, M or iaduction, B, and the permeabiHty, p, differ for the two materials. 

If a very high field is appHed the magnetisation can reach its saturated state ia which all the magnetic dipoles are aligned ia the direction of the field. If the magnetic field is switched off, the remanent magnetisation M is left. If the M (or B) is then reduced to sero, a special field strength, the coercivity, is required. 

The hysteresis loop, ia general, suppHes information about the magnetic properties such as Af, Af, preferred direction of the magnetisation or... 

The slope of the hysteresis loop in is also an important parameter. From this slope, the parameter S can be derived (17). In Figure 3 a part of the hysteresis loop (M as a function of the appHed field H) is given. The point at which M is constant as the function of the appHed field is defined as saturation magnetisation (M.). From the slope at can be written tan0 = = 1/ 1 — S ) ot dM/dH = — S ). Thus the S is defined in... 

This results ia irregular magnetisation patterns in the written transition and therefore to noise in the output signal. 

Fig. 9. The relation of an LMR and PMR transition (a) initial state of magneti2ation (b) the magnetisation and corresponding demagnetisation fields of a ...

Go Binary and Ternary Alloyed Thin Films. Most of the thin-film media for longitudinal and perpendicular recording consist of Co—X—Y binary or ternary alloys. In most cases Co—Cr is used for perpendicular recording while for the high density longitudinal media Co—Cr—X is used X = Pt, Ta, Ni). For the latter it is essential to deposit this alloy on a Cr underlayer in order to obtain the necessary in-plane orientation. A second element combined with Co has important consequences for the Curie temperature (T ) of the alloy, at which the spontaneous magnetisation disappears. The for... 

For the measurement of magnetisation in hysteresis-loop measurements, a search coil consisting of several-turn windings around a specimen is coimected to a fluxmeter whose output can be recoded on thejy-axis of an x,y plotter. The x-axis records the field strength of the primary coil around the specimen. The whole procedure can be done conveniendy in a hysteresigraph, whereby the induction is recorded automatically as the field is varied continuously. 

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