6 Experimental Results 6.8 High resolution magnetic patterning of exchange coupled multilayers

The antiferromagnetic interlayer exchange coupling between two ferromagnetic layers separated by a thin nonmagnetic spacer was discovered in 1986 by Grünberg et al. [1]. Since then this phenomenon has been intensively studied (for a recent review see [2]) because of its potential for the creation of antiferromagnetically coupled media for high-density magnetic recording [3, 4] and artificial antiferromagnets that are used as hard magnetic electrodes for magnetic memory elements [5, 6] and magnetoresistive sensors [7]. Recently it was shown [8], that the type of the interlayer exchange coupling between two iron layers separated by a chromium spacer can be easily modified by ion irradiation. This modification is a result of the atomic intermixing at the Fe/Cr interface caused by the dissipation of energy of ions due to their collisions within the crystalline lattice. The intermixing at the Fe/Cr interface leads to the appearance of microscopic “magnetic bridges ” that connect the two iron films and provide strong direct local ferromagnetic coupling between them. With increase of the irradiation fluence the quantity of magnetic bridges increases and the type of interlayer coupling changes to the ferromagnetic one. Since the direct coupling through a bridge is about hundred times stronger than that via the spacer the density of bridges and, consequently, the ion fluences necessary to chang