Direct observation of pinned / biased moments in magnetic superlattices

We report the pinned/biased moment in the superlattices consisting of ferro-magnetic (FM) SrRuO 3 and antiferromgnetic (AFM) SrMnO 3. This superlat-tice system shows anisotropy and oriented pinning/biasing in the field-cooled (FC) hysteresis loop. The in-plane cooling-field provides antiferromagnetic orientations while out-of-plane cooling-field provides ferromagnetic orienta-tions to the pinned/biased moments. The spacer layer thickness, strength and orientation of magnetic field, cooling field, and driving current influence the pinning strength. We propose that the magnetic structure is a repetition of AF M/P in/F M (F ree)/P in unit below a critical field to explain its magnetic and transport properties. The transport behavior is discussed using the spin-dependent conduction. 1 A biased magnetic field has been observed on cooling the FM-AFM system below the Curie temperature (T C) of the F M through the Neel temperature (T N) of the AF M in presence of a magnetic field 1–5. It is belived that the biased field is responsible for the shift of the hysteresis loop along the field axis which has been observed in a wide variety of F M − AF M systems, many of which do not exhibit a simple spin structure at the interface to the F M-AFM layers or materials. In general, a biased field is established through field-cooling in the film plane where the magnetic easy axis of soft ferromagnetic materials normally lies in plane. A shift in hysteresis loop along the magnetization axis in addition to the shift along the field axis is also observed 6. The authors have explained the shift in hysteresis loop along the magnetization axis by the pinned uncompensated spin at the interfaces. Recently Maat et al. 7 have shown that exchange bias can also be observed for the magnetization perpendicular to the film plane in Co/P t multilayers biased by CoO. They investigated the biasing in various directions and found substantially more within the sample plane, which they related to the anisotropy of the single-q spin structure of the CoO. Several theoretical models have been proposed to explain the origin of the biased field. Indeed, most of the theoretical models assume a single domain state of the ferromagnetic layer and focus on the domain structure of the AF M layer for different types of interfaces. However, despite the enormous research done in this field, this effect is poorly understood. Here, we report the direct observation of pinned/biased moments of the SrRuO 3 …