Saturation remanence

A second type of behavior existing in the PLZT s is the linear (Pockels) effect which is generally found in high coercive field, tetragonal materials (composition 3), This effect is so named because of the linear relationship between An and electric field. The truly linear, nonhysteretic character of this effect has been found to be intrinsic to the material and not due to domain reorientation processes which occur in the quadratic and memory materials. The linear materials possess permanent remanent polarization however, in this case the material is switched to its saturation remanence, and it remains in that state. Optical information is extracted from the ceramic by the action of an electric field which causes linear changes in the birefringence, but in no case is there polarization reversal in the material. 

The experimental setup for observing this effect, as seen in Figure 8, is identical to that for the quadratic response, except that the PLZT plate is prepoled to saturation remanence before using. Applications include modulators and spectral filters however, no devices have yet emerged utilizing this effect. 

To further confirm the nature of magnetic interactions, the isothermal remanence magnetization (IRM) curve Mr(H) and DC demagnetization (DCD) curve A1d(H), both normalized to the saturation remanence, have been plotted at 20K. From these curves, a Henkel plot has been obtained (Fig. 2l.l0a). In a perfectly noninteracting system of single-domain particles, the slope of the Henkel plot should be —2 and the experimental points would lie on the upper limit of this plot [37], The types of interactions are characterized by means of 8M plots (Fig. 21. lOb) obtained using the following relation ... 

Fig. 24. Temperature dependence of the saturated remanent magnetization in Eu . i Sro oS (from Maletta and Felsch 1979b).

Fig. 26. Saturated remanent magnetization as a function of time (logarithmic) for (La , gGd j)Al, at various temperatures (from von Lohneysen and Tholence 1979).

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. 

When the substrate is parallel to the applied field, the remanence-to-saturation-mag-netization ratio is 0.60. The hysteresis loop is squarer than that obtained with the particles dispersed in solution. 

When the substrate is perpendicular to the applied field, the hysteresis loop is smoother. The remanence-to-saturation-magnetization ratio, MrlM, decreases to 0.4. 

This clearly shows that, for a given saturation magnetization, the remanence magnetization, Mr, markedly varies with the orientation of the applied field. This change is at-... 

Hysteresis curves for a magnetically hard and a magnetically soft ferromagnetic material. S = saturation magnetization, R = remanent magnetization, K = coercive force... 

Fig. II. (a) Temperature dependence of the magnetization for 200-nm thick Ga, MnrAs with x =0.053. The magnetic field is applied perpendicular to the sample surface (hard axis). The inset shows the temperature dependence of the remanent magnetization (0 T) and the magnetization at 1 T in a field parallel to the film surface, (b) Temperature dependence of the saturation magnetization determined from the data shown in (a) by using ArTott plots (closed circles). Open circles show inverse magnetic susceptibility and the Curie-Weiss fit is depicted by the solid straight line (Ohno and Matsukura 2001).

The saturation magnetization Ms is a specific constant for the material and for magnetic iron oxides is principally determined by the Fe2 + ion content. The ratio of remanent magnetization to saturation magnetization (Mr/Ms) for the tape depends mainly on the orientation of the pigment needles with respect to the longitudinal direction of the tape, and should approach the theoretical maximum value of unity as closely as possible. 

Pmax+ — Prrei—) change of polarization when the sample is switched from the negative state of the relaxed remanent polarization into the positive saturation -switching case... 

The third loop establishes the sample into the positive remanent polarization state without sampling data. The fourth loop now starts in the positive relaxed remanent polarization state (Prrei+), turns into the negative saturation (Pmax-), then crosses the polarization axis at zero volts excitation signal in the negative remanent polarization state (Pr ). Afterwards the sample is driven into the positive saturation (Pmax+) and ends up in the positive remanent polarization state (Pr+) when the voltage is zero again. Subsequently, the hysteresis loop is balanced respectively to the values P(+Vmax) and P(-Vmax). From the data of the second loop the parameters Vc-, Pr, Prrei- are determined and from the data of the fourth loop the parameters Vc+, Pr+, Prrei+ The closed hysteresis loop (continuous loop) can be calculated from the second half of the second loop and the second half of the fourth loop. 

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