Co-Ti and Ru-Ti substituted barium ferrite nanocrystalline particles BaFe12−2xCoxTixO19 with (0≤x≤1) and BaFe12−2xRuxTixO19 with (0≤x≤0.6) were prepared by ball milling method, and their magnetic properties and their temperature dependencies were studied. The zero-field-cooled (ZFC) and field-cooled (FC) processes were recorded at low magnetic fields and the ZFC curves displayed a broad peak at a temperature TM. In all samples under investigation, a clear irreversibility between the ZFC and FC curves was observed below room temperature, and this irreversibility disappeared above room temperature. These results were discussed within the framework of random particle assembly model and associated with the magnetic domain wall motion. The resistivity data showed some kind of a transition from insulator to perfect insulator around TM. At 2 K, the saturation magnetization slightly decreased and the coercivity dropped dramatically with increasing the Co-Ti concentration x. With Ru-Ti substitution, the saturation magnetization showed small variations, while the coercivity decreased monotonically, recording a reduction of about 73% at x = 0.6. These results were discussed in light of the single ion anisotropy model and the cationic distributions based on previously reported neutron diffraction data for the CoTi substituted system, and the results of our Mössbauer spectroscopy data for the RuTi substituted system.

We report results of measurements of the perpendicular [current perpendicular to the layer planes (CPP)] and parallel [current in the layer planes (CIP)] magnetoresistances (MRs) of Co/Ag multilayers having Co and Ag thicknesses $t_{\mathrm{Co}}$ and $t_{\mathrm{Ag}}$ ranging from 1.5 to 60 nm. (1) We find the variations of the CPP- and CIP-MRs with $t_{\mathrm{Ag}}$ and $t_{\mathrm{Co}}$ to be qualitatively similar to each other, suggesting that the parameters determining both may also be similar. (2) In accord with predictions that CPP-MR>CIP-MR, we find their ratio $\pi =\mathrm{C}\mathrm{P}\mathrm{P}-\mathrm{M}\mathrm{R}/\mathrm{C}\mathrm{I}\mathrm{P}-\mathrm{M}\mathrm{R}$ to range from about 3 to at least 6. (3) We analyze current perpendicular to the layer plane (CPP) specific resistances, ${\mathrm{Ar}}_t$, of Co/Ag multilayers having a wide range of Co and Ag thicknesses $t_{\mathrm{Co}}$ and $t_{\mathrm{Ag}}$ in terms of a two-current, series resistor model based upon the assumption that the spin-diffusion lengths in the Co and Ag are much longer than $t_{\mathrm{Co}}$ and $t_{\mathrm{Ag}}$, respectively. We show first that a six parameter fit gives rather good agreement with four data sets, with the three parameters that can be separately checked agreeing within experimental uncertainties with independent measurements of the same quantities. We then examine the ability of these fits to predict the behavior of additional sets of data. Here we find some agreements and some disagreements. Possible reasons for the disagreements are examined.