X-ray magnetic circular dichroism (XMCD) measured at T=6$\hskip0.3em${}K and $\mu${}0H=5$\hskip0.3em${}T on the $\alpha${}-phase Fe-phthalocyanine (FePc) textured thin films shows that the Fe2+ ions present an unusually large, highly unquenched mL=0.53\ifmmode\pm\else\textpm\fi{}0.04$\hskip0.3em${}$\mu${}B orbital component, with planar anisotropy. The spin mS=0.64\ifmmode\pm\else\textpm\fi{}0.05$\hskip0.3em${}$\mu${}B and the intra-atomic magnetic dipolar mT components were also obtained. The mL/mS=0.83 ratio is the largest measured in 3d complexes and compounds. The origin of this unusually high orbital moment is the incompletely filled eg level lying close to the Fermi energy. This explains the unusually large and positive hyperfine field detected by M\"ossbauer spectroscopy in FePc. The FePc film strong planar anisotropy inferred from XMCD experiments is fully confirmed by magnetization measurements.

Ultrathin cobalt phthalocyanine transistors of 4 ML have been fabricated for chemical sensing. Compared to 50 ML devices, the ultrathin transistors show faster response times, higher base line stabilities, and sensitivity enhancements of 1.5–20 for the five analytes tested. The enhanced response for the ultrathin transistors provides insight into the device physics. The absorption of analytes changes the surface doping level and trap energies. The changes in surface trap energies perturb the charge transport properties of the ultrathin devices, thereby, making these devices more sensitive.

A unidirectional coercivity enhancement, exhibiting the same behavior as a positive exchange bias, has been discovered in a temperature range below the blocking temperature in Co/CoO bilayers. Below this temperature range, the usual shift of the center of the $\mathrm{M–H}$ loops to the negative or antiparallel to the cooling field direction is found. This behavior is observed in both magnetic hysteresis loops and transport properties. The positive exchange bias can be explained by reversible changes in the interfacial pinning by the antiferromagnet causing an asymmetric magnetization reversal and a unidirectional coercivity enhancement along the cooling field direction.

It is shown that polarized neutron reflectometry can determine in a model-free way not only the mean magnetization of a ferromagnetic thin film at any point of a hysteresis cycle, but also the mean-square dispersion of the magnetization vectors of its lateral domains. This technique is applied to elucidate the mechanism of magnetization reversal of an exchange-biased Co/CoO bilayer. The reversal process above the blocking temperature $T_b$ is governed by uniaxial domain switching, while below $T_b$ the reversal of magnetization for the trained sample takes place with substantial domain rotation.

The magnetization reversal in exchange coupled polycrystalline Co/CoO bilayers has been investigated as a function of CoO thickness using anisotropic magnetoresistance as a probe. The anisotropic magnetoresistance (AMR) was measured during the magnetization reversal and it was used to determine the orientation of the magnetization. For thin CoO layers large training effects were present; ergo the first hysteresis loop after field cooling was not the same as the second. The magnitude of the observed training was found to decrease with increasing CoO thickness. In the samples where substantial training was observed, the first magnetization reversal was dominated by nucleation of reversed domains. For the reversal from the antiparallel state back to the parallel direction, the AMR is consistent with a rotation process. In thicker CoO films where the training was less, the asymmetry was drastically reduced. A simple model that couples the antiferromagnetic grains to the ferromagnetic layer simulates qualitatively the observed magnetoresistance.

The temperature dependence of the magnetization reversal process, reversible and irreversible exchange bias anisotropy, uniaxial anisotropy, and rotational hysteresis of polycrystalline exchange-biased $\mathrm{Co}∕\mathrm{Co}\mathrm{O}$ bilayers have been investigated. A dichotomy in the experimental results is found for thin and thick CoO layers with the boundary near $7\mathrm{nm}$. The uniaxial anisotropy in thin (thick) CoO films is small (large), whereas the rotatable anisotropy is large (small). At low temperatures, the asymmetry in the magnetization reversal is due to instabilities at the antiferromagnet interface. Near the blocking temperature, a different asymmetry is due to a broad distribution of large grains. Near the latter temperature range, the smaller grains dissipate energy as evidenced by an increased rotational anisotropy and training of the hysteresis loop. All features can be understood qualitatively with a distribution of independent antiferromagnetic grains coupled to the ferromagnetic film.