3.3.1 Introduction

It has been recently underlined that tilted magnetic media can have considerable advantages in magnetic recording applications [74,75,76]. These media are usually realized as thin films constituted by grains with easy axis at an angle of approximately 45$^\circ$ with respect to the film plane (see for example Fig. 3.14). This leads to coercive fields smaller by a factor two compared to perpendicular media^3.4, and thus allows the use of high anisotropy magnetic materials, which in turn provide a better thermal stability or a higher areal density. Higher data rates can be also realized owing to the high torque that acts on the magnetization and the high signal-to-noise ratio (SNR) related to the fact that grains with slightly different easy axes have almost the same switching field^3.5. As mentioned before, in these media it is possible to realize switching for external fields below the Stoner-Wohlfarth (SW) limit [75], and, in the appropriate range of external field amplitude, it has been shown that the switching time decreases with decreasing amplitude of the external field pulse [76]. In the following we intend to analyze the switching process in weakly coupled granular tilted media. As first approximation we will analyze the case of noninteracting grains. Since the grains are usually almost uniformly magnetized, this case can be treated by using the uniform mode theory. In this respect, we consider a family of noninteracting grains with dispersion in the easy axis and initial magnetization directions. This analysis provides an estimate of the range of external field amplitude and directions required to realize switching. The parameter values predicted by the theory are then used in a 3D micromagnetic simulation of the switching process in which the interactions of the grains are taken into account.

Figure 3.14: Granular structure of perpendicular and tilted media.