No abstract

Exchange bias (EB) is a shift of the hysteresis loop from its normal position, symmetric around H = 0, to H E = 0. It occurs when thin ferromagnetic (F) films are deposited on a variety of antiferromagnetic (AF) materials. EB is also associated with several additional remarkable features: i) the bulk magnetizations of the F is orthogonal to the AF easy axis; ii) H E is of similar magnitude for compensated and uncompensated AF interface layers; iii) the sign of H E can assume both positive and negative values; and, iv) the magnetizationwhere Hc is the coercive field. Here we propose a model that describes the EB phenomenon for a compensated interface. Based on the experimental evidence, and extensive computer simulations, we suggest that close to the Néel temperature a canted spin configuration in the AF interface freezes into a metastable state. As a consequence, the EB energy is reversibly stored in a spring-like magnet, or incomplete domain wall (IDW), in the F slab. The results we extract from our model, both analytically and through simulations, are qualitatively and quantitatively compatible with the available experimental information.

The lowest-energy structures of small Pd clusters ͑2 ഛ N ഛ 13͒ are computed by means of available phenomenological many-body potentials and by ab initio methods. The lowest-energy configuration is found by means of a genetic algorithm search. Satisfactory agreement between the results of the several methods implemented is achieved. Of special interest is the fact that all phenomenological potentials yield the same symmetry group for the lowest-energy cluster geometries, which moreover are identical with ab initio results. This constitutes an indication that the most common many-body empirical potentials can be trusted to yield reliable results.

When a ferromagnetic metal (F) is in contact with an antiferromagnet (AF), often a shift of the hysteresis loop away from its normal, symmetric position around H=0, to HE≠0 does occur. This phenomenon is known as exchange bias (EB). We put forward an analytic model, for compensated AF interfaces, based on the AF interface freezing into a metastable canted spin configuration. The EB energy is reversibly stored in a spring-like magnet, or incomplete domain wall, in the F slab. Our theory yields the right values of HE and its F thickness dependence HE∝tF−1. It also predicts the F layer by layer magnetization profile.

No abstract