J. B. Sousa

The onset of a Griffiths-like phase has been observed in ${\mathrm{Tb}}_{5}{\mathrm{Si}}_{2}{\mathrm{Ge}}_{2}$ (${T}_{C}=110\text{ }\text{ }\mathrm{K}$) by means of magnetic susceptibility and small-angle neutron scattering experiments. We show the growth of a ferromagnetic cluster system characterized by an inverse susceptibility exponent lower than unity at ${T}_{C}<T<{T}_{G}\ensuremath{\approx}200\text{ }\text{ }\mathrm{K}$. We suggest that the Griffiths-like state is originated by local disorder within the crystallographic structure, stabilized and enhanced by competing intralayer and interlayer magnetic interactions. Both factors thus promote segregation of nanometric regions with ferromagnetic interactions.

Dipolar superferromagnetism with reentrant low-temperature superspin glass behavior is observed on a randomly distributed ferromagnetic nanoparticle systems in discontinuous metal-insulator multilayers $[{\mathrm{Co}}_{80}{\mathrm{Fe}}_{20}(t)/{\mathrm{Al}}_{2}{\mathrm{O}}_{3}(3\mathrm{}\mathrm{n}\mathrm{m}){]}_{10}$ with nominal thickness $1.1<~t<~1.3\mathrm{nm}$ by use of ac susceptometry and dc magnetometry. At $t=1.0\mathrm{nm},$ superspin glass-like freezing is evidenced by the criticality of dynamic and nonlinear susceptibilities.

In this paper, we report on the preparation of thin films resulting from additions of Si to TiN matrix, by r.f. reactive magnetron sputtering. Results of X-ray diffraction (XRD) in both θ–2θ and α–2θ scans showed that a mixture of two phases is present, where the first is most likely fcc TiN. The higher lattice parameter of this phase, about 0.429 nm (0.424 nm for bulk TiN), could be explained by taking into account that a correction of the residual stress effect on peak positions might slightly decrease the value of the lattice parameter (around 1%). Regarding phase 2, and although the exact nature of its composition is more difficult to evaluate, we believe that it is also a cubic lattice consisting of TiSiN, where the Si could be occupying Ti positions within the TiN lattice. This would explain the low value of the lattice parameter, which by assuming a cubic structure would be 0.418 nm. Concerning texture evolution, phase 1 revealed some variations in preferential growth, which changed from 〈111〉 for low Si additions to 〈220〉 at intermediate Si additions and finally to a weak 〈200〉 texture for large Si additions. A small amorphous region of silicon nitride for large Si additions was also observed. Fourier analysis of XRD patterns showed a decrease in the size of grains for small Si additions when compared to that of TiN. For higher Si contents, only small changes were observed, although a decrease in grain size seems to be the main tendency. The grains are within the range of 4–6 nm. High-resolution transmission electron microscopy (HRTEM) on Ti0.63Si0.37N1.12 confirmed this nanocrystalline nature of the grains, revealing grains with sizes of about 2–3 nm.