The pseudo‐brookite spin‐glass system studied by means of muon spin relaxation

Zero-field muon spin relaxation (µSR) experiments have been performed on the spin glass Fe1.75Ti1.25O5. Above the spin-glass temperature of 44 K a distinct exponential µSR rate (¿) is observed, while below Tg a square-root exponential decay occurs, indicating fast spin fluctuations. Near 8 K, a maximum in ¿ is indicative of transverse spin ordering. The low ¿ values and the sharp ¿ peak at Tg are very promising for the study of spin freezing models like the Vogel–Fulcher law or the power law

Magnetic anisotropy in the cubic Laves REFe2 intermetallic compounds

In the past, the Callen–Callen (1965 Phys. Rev. 139 A455–71; 1966 J. Phys. Chem. Solids 27 1271–85) model has been highly successful in explaining the origin and temperature dependence of the magneto-crystalline anisotropy in many magnetic compounds. Yet, despite their high ordering temperatures of ~650 K, the Callen–Callen model has proved insufficient for the REFe2 compounds. In this paper, we show that it is possible to replicate the values of the phenomenological parameters K1, K2, and K3 given by Atzmony and Dariel (1976 Phys. Rev. B 13 4006–14), by extending the Callen–Callen model to second order in HCF. In particular, explanations are provided for (i) the unexpected changes in sign of K1 and K2 in HoFe2 and DyFe2, respectively, and (ii) the origin and behaviour of the K3 term. In addition, it is demonstrated that higher order terms are required, and that K4 exceeds K3 at low temperatures. Revised estimates of K1, K2, K3, K4, and K5 are given. Finally, an alternative 'multipolar' approach to the problem of magnetic anisotropy is also provided. It is shown that the latter confers significant advantages over the older phenomenological method. In particular, all the multipolar coefficients (\tilde {K}_N , N = 4, 6, 8, 10, 12) decrease monotonically with increasing temperature, with \tilde {K}_N decreasing faster than \tilde {K}_{N-2} etc. These observations are in accord with expectations based on the original Callen–Callen model