Magnetization layer-thickness dependence

Layer-thickness dependence of magnetic properties at room temperature... 

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. 

Several results about the magnetization can be found from figs. 9a and 10. To understand the layer-thickness dependence of magnetization, both the antiferromagnetic coupling of Dy and Fe moments and the modulated distribution of composition have to be taken into account, (i) Sample 5 ADy/6.25 AFc is in a state close to the compensation point the Dy moment dominates for X <6.5 A and the Fe moment dominates for X > 6.5 A. (ii) As X increases from 2.5 to 6.5 A, the magnetization magnitude of Dy/Fe,... 

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).

Figure 9b (Shen 1994) shows the Dy layer-thickness dependence of hysteresis loops of T A Dy/5 A Fe as the Dy layer thickness varies from 6.5 A to 5 A note especially (i) although the thickness interval is only 0.5 A, the coercivity and magnetization are very strongly dependent on thickness as the Dy layer thickness Y approaches 5 A where sample 5 A Dy/5 A Fe is in a state close to the compensation point, (ii) Compared with the loops in fig. 9a, the loops in fig. 9b illustrate much better squareness because these samples were coated with a 500 A SiO layer to protect fi om oxidation.

Fig. 14. Three-dimensional diagram of layer-thickness dependence of magnetization for YkDylXACo at 8kOe and 300 K (after Shan and Sellmyer 1990b).

Figure 19b (Shen 1994) shows the Dy layer-thickness dependence of hysteresis loops of Y Axb/5 AFe with fixed Fe layer thickness of 5 A. We note the similarities between fig. 19b and 9b. Because the net magnetization increases with increasing Tb layer thickness, the Tb moments, which are induced by the Fe moments at room temperature, are dominant compared with the Fe moments.

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. 

Fig. 40. Comparison of the calculated magnetization with the experimental data for (a) 6ADy/YACo (Y = 3.5, 5, 6, 8, 10, and 11), and (b) the Co layer-thickness dependence of the Co atomic fraction modulation (after Shan et al. 1990).

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. 

To reach the remanent magnetization values quoted here, the soft layer spontaneous magnetization must be higher than typically 1.6 T. Such values imply that the soft layer be a Fe based alloy. The important adjustable parameter to be considered is the layer thickness, dsoft. Based on the relation established by Skomski and Coey [80], the dsoft dependence of hn = is... 

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