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Magnetic thin films have been obtained by rf sputtering on ${\text{Si}}_{3}{\text{N}}_{4}$ substrates from a ${\text{Fe}}_{78}{\text{B}}_{13}{\text{Si}}_{9}$ target. The samples, with thickness $t$ of 80 and 305 nm, are partially amorphous; crystalline fraction increases on increasing $t$. Magnetic force microscopy and magneto-optical images, performed at the remanence on both samples, indicate that for $t=80\text{ }\text{nm}$ the average magnetization lies in the film plane, while for the largest thickness, it is oriented perpendicular to it. Static hysteresis loops have been measured at room temperature by means of a vectorial vibrating sample magnetometer with an auto-rotating head. In this way, two linearly independent components of the magnetization vector can be simultaneously acquired as a function of magnetic field either in the in-plane or out-of-plane configuration, at different angles with respect to a reference direction. In this work, the role of sample shape and magnetic anisotropy has been investigated by paying particular attention to the anhysteretic magnetization process and by considering the two-dimensional behavior of the magnetization vector. The negligible role of the in-plane shape anisotropy has been demonstrated in the specimen displaying out-of-plane anisotropy, whereas the effect of the local demagnetizing fields has been put in evidence in the sample with in-plane anisotropy.

Magnetic properties of two-dimensional ~2D! systems of magnetic nanoobjects ~2D regular lattices of magnetic nanoparticles or magnetic nanostripes! are considered. Analytical calculations of the hysteresis curve of a system with interaction between nanoobjects are provided. It is shown that during a magnetization reversal the system undergoes a number of metastable states. The kinetic problem of the magnetization reversal was solved for three models. The following results have been obtained: ~1! for a 1D system (T50) with a long-range interaction with the energy proportional to r 2 p , a staircaselike shape of the magnetization curve has a self-similar character ~complete ‘‘devil’s staircase’’ !. The nature of the steps is determined by the interplay of the interparticle interaction and the coercivity of a single nanoparticle; ~2! The influence of thermal fluctuations on the kinetic process was examined in the framework of the nearest-neighbor interaction model. The thermal fluctuations lead to additional splitting of the steps on the magnetization curve. The influence of the coercivity dispersion in the system is also discussed. A simple method to experimentally distinguish the influence of interaction from the coercivity dispersion on the magnetization curve is proposed.

Co/wedged Mn/Co sandwiches were grown on GaAs(001) at room temperature. With the magneto-optical Kerr effect technique, magnetic hysteresis loops at different Mn thicknesses $(0l~dl~4\mathrm{nm})$ were measured and the negative remanence phenomenon was clearly observed when the magnetic interlayer coupling between the two Co layers was antiferromagnetic. The mechanism can be understood with the help of a well-defined model calculation, and the result indicates that such anomalous hysteresis loops are not frequently encountered because of the critical conditions required to realize them.

A model is presented for coercivity in polycrystalline exchange-bias bilayers. It includes two contributions for their enhanced coercivity, inhomogeneous reversal, and irreversible transitions in the antiferromagnetic grains. The model can be characterized in terms of a small number of dimensionless parameters, and its behavior has been determined through simulations of magnetic reversal for a range of values of these parameters. In these simulations, the first contribution to the coercivity arises from energy losses in the ferromagnet due to irreversible transitions over small, local energy barriers in the ferromagnetic film due to the inhomogeneous coupling to the antiferromagnet. This inhomogeneous reversal contributes to the coercivity at all temperatures. The second contribution to the coercivity arises from energy losses in the antiferromagnet due to irreversible transitions of the antiferromagnetic order in the grains. In the present model, the antiferromagnetic order only becomes unstable at nonzero temperature, so that this contribution to the coercivity only occurs at nonzero temperatures. In addition to the coercivity, the computed hysteresis loops are found to be asymmetric, and the loop shift is shown to differ from the grain-averaged unidirectional anisotropy.

We analyze the coercivity, remanence, and initial magnetization of a single-domain, single-component amorphous material. We assume a uniform ferromagnetic exchange and concentrate on the effect of single-ion anisotropy. We find a threshold anisotropy below which the coercivity is zero. At large anisotropy, the coercivity is proportional to the anisotropy energy. Exchange pulling increases the remanence of amorphous materials. We suggest that exchange pulling between crystallites may also be operative in small-grain metallic polycrystals.

Magnetization measurements are presented of $\mathrm{Au}\mathrm{Fe}$ alloys containing 0.002, 0.005, and 0.01 at.% Fe over the temperature range 1.5-120 \ifmmode^\circ\else\textdegree\fi{}K and in magnetic fields up to 60 kG. From low-field susceptibility measurements we find a spin $S$ of 1.29 \ifmmode\pm\else\textpm\fi{} 0.03 and a Kondo temperature ${T}_{K}$ of (0.10 \ifmmode\pm\else\textpm\fi{} 0.01) \ifmmode^\circ\else\textdegree\fi{}K for the $\mathrm{Au}\mathrm{Fe}$ system. It is shown that recent perturbation calculations of the magnetization for $T\ensuremath{\gg}{T}_{K}$ can be expressed as a Brillouin function with spin $S$ and a modified $g$ factor dependent on temperature, applied field, and ${T}_{K}$. Magnetization curves computed from the values of ${T}_{K}$ and $S$ determined from low-field susceptibility measurements are found to be in good agreement with the measured magnetization over a wide range of fields and temperatures.