Magnetocrystalline anisotropy of ε-Fe2O3

Abstract

The epsilon Fe2O3 phase of iron oxide has been studied to understand the spin structure and the magnetocrystalline anisotropy in the bulk and in thin films of ε-Fe2O3 and Co-doped ε-Fe2O3. The preferential magnetization direction in the nanoparticles of ε-Fe2O3 is along the a-axis [M. Gich et al., Chem. Mater. 18, 3889 (2006)]. Compared to the bulk band gap of 1.9 eV, the thin-film band gap is reduced to 1.3 eV in the Co-free films and to 0.7 eV in the film with partial Co substitution. The easy magnetization direction of the bulk and Co-free ε-Fe2O3 is along the c-axis, but it switches to the a-axis on Co substitution. All three systems exhibit in-plane anisotropies associated with the orthorhombic crystal structure of the oxide.

Controlling the magnetocrystalline anisotropy of ε-Fe2O3

“…Our DFT optimized lattice parameters obtained for ε-Fe 2 O 3 are as a = 5.125, b = 8.854 and c = 9.563 Å, 33,34 which is in agreement with the experimental lattice parameters of Sect. I.…”

“…Our calculated electronic structure yields an energy band-gap of 1.9 eV. 33,34 Figure 2 shows the unit-cell structures of the Co-substituted ε-Fe 2 O 3 . For the Co-substitution, we kept the volume of the unit cell constant and only the ionic positions were relaxed.…”

Heterostructures of ε-Fe2O3 and α-Fe2O3: insights from density functional theory

“…Here we are interested in iron oxides that have demonstrated potential as photocatalysts, but suffer from high recombination. Bulk 3-Fe 2 O 3 is an indirect band-gap semiconducting material with a gap of 1.9 eV, 10,11 whereas bulk a-Fe 2 O 3 is a direct band-gap semiconducting material with 2.2 eV of band-gap. 12,13 Bulk 3-Fe 2 O 3 is magnetically hard with a room temperature coercivity of 20 kOe, [14][15][16] while bulk a-Fe 2 O 3 is magnetically very so with a room temperature coercivity of a few 100 Oe.…”

Magnetic properties and resistive switching in mixture films and nanolaminates consisting of iron and silicon oxides grown by atomic layer deposition

“…In accord with the literature, the orthorhombic ε-Fe2O3 has emerged as possibly the most interesting phase of iron oxide, mainly due to its ferromagnetic performance with remarkable coercive field at low and room temperatures, as well as magnetoelectric properties. [38][39][40][41][42][43][44][45][46] As already noted, the ε-Fe2O3 has been recognized as a metastable phase of iron oxide, which can be achieved only in nanocrystalline material upon polymorphous transformation between maghemite (-Fe2O3) and hematite (-Fe2O3) phases. 33,47-49 Magnetic ε-Fe2O3 nanoparticles have earlier been prepared often by wet chemical synthesis.…”

“…33,47-49 Magnetic ε-Fe2O3 nanoparticles have earlier been prepared often by wet chemical synthesis. 38,44,45,50,51 In the present study, the magnetic behavior of the triple Fe2O3-SiO2-Fe2O3 layer, in which the content of -Fe2O3 was significant (Fig. 2), resembles that observed by Li et al 34 In the latter work, iron oxide nanocrystals were stabilized within spaces confined inside mesoporous silica after annealing in order to crystallize the -Fe2O3 phase, and the coercivities were in the range of 2000-2500 Oe, as measured below room temperature, i.e.…”