Spin flop in goethite

Abstract

A spin-flop transition is observed when a field of 20 T is applied parallel to the h axis of a specimen of natural goethite at 4.2 K. The gwthite orders in a four-sublattice antiferromagnetic structure with the sublattice magnetizations inclined at i I 3 ' to b, and an iron moment of 3.90 pg. There is a small net ferromagnetic moment of 0.004 pg along b which has the eRect of more than doubling fhe threshold field for spin flop. The anisotropy field is deduced to be 0.1 1 T. cotresponding to a uniaxial anisotropy energy K = 6 x IO4 J d. The origin of the weak moment is discussed. and it is suggested that mode superparmgnefism may arise in non-collinear antiferromagnets when two transverse spin configurations xe effectively degenerate.

Arsenic Adsorption onto Minerals: Connecting Experimental Observations with Density Functional Theory Calculations

“…The DFT+U correction [166,167] was employed with a U = 4 eV for Fe and 0 eV for all other elements. Spin states were ordered according to the experimental observed magnetic ordering of goethite [168]. These selections have worked reasonably well in a previous study on goethite and goethite-water [73].…”

Constraining the Origins of the Magnetism of Lepidocrocite (γ-FeOOH): A Mössbauer and Magnetization Study

“…The χ AFM -value determined for our lepidocrocite sample, 5.34 × 10 −7 m 3 /kg, leads to T N = 392 K. For comparison, χ AFM in goethite is 3.96 × 10 −7 m 3 /kg (Coey et al, 1995), which corresponds to a theoretical value of T N = 532 K, close to the actual Néel temperature of about 400 K (e.g., Özdemir and Dunlop, 1996). In our lepidocrocite sample, the Néel temperature (ca.…”

Magnetic dynamics of weakly and strongly interacting hematite nanoparticles

“…However, the model used to calculate the field dependence of the Mössbauer spectra and the spin-flop field was based on the assumption of uniaxial anisotropy and a collinear antiferromagnetic structure, although the magnetic structure of goethite is much more complicated. 43 Therefore the model seems to be too crude. Secondly, it has been shown that even a very small uncompensated magnetic moment in antiferromagnetic particles can result in a substantial increase of the spin-flop field, 43,44 and small antiferromagnetic particles will inevitably have an uncompensated moment.…”

“…43 Therefore the model seems to be too crude. Secondly, it has been shown that even a very small uncompensated magnetic moment in antiferromagnetic particles can result in a substantial increase of the spin-flop field, 43,44 and small antiferromagnetic particles will inevitably have an uncompensated moment. Furthermore, the anisotropy was estimated at low temperatures, but at higher temperatures, at which the model is applied, the anisotropy may be smaller.…”