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.

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.

Magnetization reversal was studied in square arrays of square Co/CoO dots with lateral size varying between 200 and 900 nm. While reference nonpatterned Co/CoO films show the typical shift and increased width of the hysteresis loop due to exchange bias, the patterned samples reveal a pronounced size dependence. In particular, an anomaly appears in the upper branch of the magnetization cycle and becomes stronger as the dot size decreases. This anomaly, which is absent at room temperature in the patterned samples, can be understood in terms of a competition between magnetostatic interdot interaction and exchange anisotropy during the magnetic switching process.

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Exchange coupling in patterned exchange-biased NiFe/ CoO squares with different sizes has been studied. Arrays of square dots with the lateral size varying between 300 and 900 nm and a fixed interdot distance of 800 nm were prepared by sputtering followed by in situ oxidation. Exchange bias in the initial and trained loops was studied as a function of the size, temperature, and cooling field. A decrease in the exchange bias shift was observed with a decreasing size, which might be due to the magnetostatic interdots interaction. For the trained loops, a variation of exchange bias with the temperature and cooling field, similar to those observed in continuous films, was observed.