Anisotropy layer-thickness dependence

Layer-thickness dependence of magnetic properties at room temperature. Figure 9a (Shan and Sellmyer 1990b) shows a detailed Fe layer-thickness dependence of hysteresis loops for 5 A DylX A Fe as the Fe layer thickness varies from 2.5 A to 40 A note especially that the interval is only 1.25 A asX ranges from 2.5 to 10 A. The layer-thickness dependences of magnetization and anisotropy determined from fig. 9a are summarized in fig. 10. 

Fig. 10. Fe layer-thickness dependence of magnetization and measured anisotropy for 5 A Dy/JT A Fe at 300K (after Shan and Selhnyer 1990b).

Fig. 15. Three-dimensional diagram of layer-thickness dependence of intrinsic anisotropy for T A Dyixk Co...

Fig. 18. Dy layer-thickness dependence of magnetization and anisotropy for K AOy/6 ACo at 300 K and 4.2 K (after Shan and Sellmyer 1990b).

Figure 40 shows tire Co layer-thickness dependence of the average values of the total magnetization a, Co- and Dy-subnetwork magnetization Oco and Ooy (fig. 40a) and the Co-atomic fraction modulation j4 , i.e. A in eq. (6) (fig- 40b). It is seen that the calculated a value agrees with the experimental data quite well the A value is only about 0.1 for the thinnest Co layer thickness of 3.5 A and its value increases as Co layer becomes thicker. The data shown in fig. 40 will be used to illustrate the calculation of the magnetic anisotropy. 

When the anisotropy energy within the hard layer cannot be considered as infinite as compared to the Zeeman energy, the nucleation field depends on the hard layer magnetic properties [122], However, as long as <7hard > 34ard ( hard and 4ard are the hard layer thickness and domain wall width respectively), Hn does not depend much on dhard. For 10 nm, the room temperature nucleation field jU()Hn is typically 1 T. 

Figure 11 Investigation of the impact of anisotropy on the ellipsometric signal. The ellipsometric signal dA calculated in dependence of the number density of adsorbed molecules N. A molecular length of 2.1 nm and a refractive index of riaxis = 1-56 for an E-vector along and of np rp = 1.48 for an E-vector perpendicular to the molecular axis were used. The layer thickness (l.Onm to 1.9nm), the tilt angle (70° down to 40°), n, and were all assumed to be dependent on the surface coverage.

Texture transitions are particularly pronounced when an electric field is applied to materials having a large dielectric anisotropy. A planar texture undergoes transition to a quasihomeotropic optically transparent texture via intermediate structural defects [150,151]. The threshold voltage observed experimentally for a transition from a planar to a homeotropic texture depends on the layer thickness according to f/oc (for the Frederiks transition the threshold voltage is independent of thickness). A model that accounts for the experimental data (at least partly) has been developed by Parodi [152] who assumed the formation of transition layers between the surface and the bulk of a sample. A discrepancy between the calculated and observed periods of the texture instability may be due to a nonuniform... 

The relaxation time constant T is proportional to the rotational viscosity coefficient. Furthermore, it depends on the layer thickness a and the elastic coefficient 22 ot the anisotropy of the magnetic susceptibility and the critical field strength Hf. for this geometry. Two of these quantities have to be determined in a separate experiment. 

Both in theory and experiments, surface magnetism is mostiy probed for surfaces of ultrathin ferromagnetic films (not for bulk materials). Therefore, it is not easy to separate surface effects from effects associated with reduced film thickness. Usually, the surface information is extracted from the thickness dependence of the quantity, which is analyzed. The surface anisotropy is a typical example for this approach (Section 7.6.1). Also, calculations are performed for slabs consisting of only a few atomic layers. Thus, it is important to remember that the surface magnetism quantities could be, in general, strongly dependent on the slab thickness. 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

The magnetic properties of Co/Pt MLs depend on the thicknesses of the individual layers, /p and tCo (57). For tCo <1.2 nm, the axis of easy magnetization is perpendicular to the surface, as desired for MO recording. The maximum anisotropy is found for tCo = 0.4 nm, corresponding to two atomic layers. Square hysteresis loops with 100% remanence are observed for tCo < 0.5 nm and a total ML thickness of about 20 nm. A practically used configuration is, eg, 14x (0.4 nm Co +1.2 nm Pt). The information in these media is magnetically stored in about 30 layers of magnetic Co atoms. 

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