Cobalt carbide nanoparticles were processed using polyol reduction chemistry that offers high product yields in a cost effective single-step process. Particles are shown to be acicular in morphology and typically assembled as clusters with room tempe
rature coercivities greater than 4 kOe and maximum energy products greater than 20 KJ/m3. Consisting of Co3C and Co2C phases, the ratio of phase volume, particle size, and particle morphology all play important roles in determining permanent magnet properties. Further, the acicular particle shape provides an enhancement to the coercivity via dipolar anisotropy energy as well as offering potential for particle alignment in nanocomposite cores. While Curie temperatures are near 510K at temperatures approaching 700 K the carbide powders experience an irreversible dissociation to metallic cobalt and carbon thus limiting operational temperatures to near room temperature.
We have formulated a relaxation mechanism for ferrites and ferromagnetic metals whereby the coupling between the magnetic motion and lattice is based purely on continuum arguments concerning magnetostriction. This theoretical approach contrasts with
previous mechanisms based on microscopic formulations of spin-phonon interactions employing a discrete lattice. Our model explains for the first time the scaling of the intrinsic FMR linewidth with frequency, and 1/M temperature dependence and the anisotropic nature of magnetic relaxation in ordered magnetic materials, where M is the magnetization. Without introducing adjustable parameters our model is in reasonable quantitative agreement with experimental measurements of the intrinsic magnetic resonance linewidths of important class of ordered magnetic materials, insulator or metals.
Nano granular metallic iron (Fe) and titanium dioxide (TiO$_{2-delta}$) were co-deposited on (100) lanthanum aluminate (LaAlO$_3$) substrates in a low oxygen chamber pressure using a pulsed laser ablation deposition (PLD) technique. The co-deposition
of Fe and TiO$_2$ resulted in $approx$ 10 nm metallic Fe spherical grains suspended within a TiO$_{2-delta}$ matrix. The films show ferromagnetic behavior with a saturation magnetization of 3100 Gauss at room temperature. Our estimate of the saturation magnetization based on the size and distribution of the Fe spheres agreed well with the measured value. The film composite structure was characterized as p-type magnetic semiconductor at 300 K with a carrier density of the order of $ 10^{22} /{rm cm^3}$. The hole carriers were excited at the interface between the nano granular Fe and TiO$_{2-delta}$ matrix similar to holes excited in the metal/n-type semiconductor interface commonly observed in Metal-Oxide-Semiconductor (MOS) devices. From the large anomalous Hall effect directly observed in these films it follows that the holes at the interface were strongly spin polarized. Structure and magneto transport properties suggested that these PLD films have potential nano spintronics applications.
Alternating layers of granular Iron (Fe) and Titanium dioxide (TiO$_{2-delta}$) were deposited on (100) Lanthanum aluminate (LaAlO$_3$) substrates in low oxygen chamber pressure using a controlled pulsed laser ablation deposition technique. The total
thickness of the film was about 200 nm. The films show ferromagnetic behavior for temperatures ranging from 4 to $400 ^oK$. The layered film structure was characterized as p-type magnetic semiconductor at $300 ^oK$ with a carrier density of the order of $10^{20} /cm^3$. The undoped pure TiO$_{2-delta}$ film was characterized as an n-type magnetic semiconductor. The hole carriers were excited at the interface between the granular Fe and TiO$_{2-delta}$ layers similar to holes excited in the metal/n-type semiconductor interface commonly observed in Metal-Oxide-Semiconductor (MOS) devices. The holes at the interface were polarized in an applied magnetic field raising the possibility that these granular MOS structures can be utilized for practical spintronic device applications.
