We report on the coupling between ferroelectric and magnetic order parameters in a nanostructured BaTiO ₃ -CoFe ₂ O ₄ ferroelectromagnet. This facilitates the interconversion of energies stored in electric and magnetic fields and plays an important role in many devices, including transducers, field sensors, etc. Such nanostructures were deposited on single-crystal SrTiO ₃ (001) substrates by pulsed laser deposition from a single Ba-Ti-Co-Fe-oxide target. The films are epitaxial in-plane as well as out-of-plane with self-assembled hexagonal arrays of CoFe ₂ O ₄ nanopillars embedded in a BaTiO ₃ matrix. The CoFe ₂ O ₄ nanopillars have uniform size and average spacing of 20 to 30 nanometers. Temperature-dependent magnetic measurements illustrate the coupling between the two order parameters, which is manifested as a change in magnetization at the ferroelectric Curie temperature. Thermodynamic analyses show that the magnetoelectric coupling in such a nanostructure can be understood on the basis of the strong elastic interactions between the two phases.

The occurrence of room temperature ferromagnetism is demonstrated in pulsed laser deposited thin films of ${\mathrm{S}\mathrm{n}}_{1-x}{\mathrm{C}\mathrm{o}}_x{\mathrm{O}}_{2-\delta }$ ($x<0.3$). Interestingly, films of ${\mathrm{S}\mathrm{n}}_{0.95}{\mathrm{C}\mathrm{o}}_{0.05}{\mathrm{O}}_{2-\delta }$ grown on $R$-plane sapphire not only exhibit ferromagnetism with a Curie temperature close to 650 K, but also a giant magnetic moment of $7.5\pm 0.5{\mu }_B/\mathrm{C}\mathrm{o}$, not yet reported in any diluted magnetic semiconductor system. The films are semiconducting and optically highly transparent.

In this paper we report on a systematic investigation, in the $5\text{to}300\mathrm{K}$ temperature regime, of the electronic, magnetotransport, thermoelectric, thermal, and elastic properties of four $M_2\mathrm{Al}\mathrm{C}$ phases: ${\mathrm{Ti}}_2\mathrm{Al}\mathrm{C}$, ${\mathrm{V}}_2\mathrm{Al}\mathrm{C}$, ${\mathrm{Cr}}_2\mathrm{Al}\mathrm{C}$, and ${\mathrm{Nb}}_2\mathrm{Al}\mathrm{C}$. The electrical conductivity, Hall coefficient, and magnetoresistances are analyzed within a two-band framework assuming a temperature-independent charge carrier concentration. As with other $MAX$-phase materials, these ternaries are nearly compensated, viz. the densities and mobilities of electrons and holes are almost equal. There is little correlation between the Seebeck and Hall coefficients. With Young’s and shear moduli in the $270\mathrm{GPa}$ and $120\mathrm{GPa}$ range, respectively, the phases studied herein are reasonably stiff. With room temperature thermal conductivities in the $25\mathrm{W}∕\mathrm{m}\mathrm{K}$ range ($45\mathrm{W}∕\mathrm{m}\mathrm{K}$ for ${\mathrm{V}}_2\mathrm{Al}\mathrm{C}$) they are also good thermal conductors.

Pulsed laser deposited films of Co-doped anatase ${\mathrm{TiO}}_2$ are examined for Co substitutionality, ferromagnetism, transport, magnetotransport, and optical properties. Our results show limited solubility (up to ∼2%) of Co in the as-grown films and formation of Co clusters thereafter. For the ${\mathrm{Ti}}_{0.93}{\mathrm{Co}}_{0.07}{\mathrm{O}}_{2-\delta }$ sample, which exhibits a Curie temperature ${(T}_C)$ over 1180 K, we find the presence of 20–50 nm Co clusters as well as a small concentration of Co incorporated into the remaining matrix. After being subjected to the high-temperature anneal during the first magnetization measurement, the very same sample shows a $T_C\sim 650\mathrm{K}$ and almost full matrix incorporation of Co. This $T_C$ is close to that of as-grown ${\mathrm{Ti}}_{0.99}{\mathrm{Co}}_{0.01}{\mathrm{O}}_{2-\delta }$ sample (∼700 K). The transport, magnetotransport, and optical studies also reveal interesting effects of the matrix incorporation of Co. These results are indicative of an intrinsic ${\mathrm{Ti}}_{1-x}{\mathrm{Co}}_x{\mathrm{O}}_{2-\delta }$ diluted magnetic semiconductor with $T_C$ of about 650–700 K.