The magnetic transition in ε-Fe2O3 nanoparticles: Magnetic properties and hyperfine interactions from Mössbauer spectroscopy

Abstract

The nanoparticles of ε-Fe2O3 enriched with 57Fe isotope in amorphous silica matrix were prepared by sol-gel technique starting from a single molecular precursor for both Fe2O3 and silica. From the X-ray powder diffraction pattern ε-Fe2O3 was identified as the major phase and α-Fe2O3 and β-Fe2O3 were observed as minor iron oxide phases. Using the log-normal distribution for fitting the experimental data from the TEM micrographs, the characteristic size of particles d0 ∼ 25 nm was derived. The rather high coercivity of ∼2.1 T at room temperature was confirmed for our nanoparticle system. From the dependences of magnetization on temperature a two-step magnetic transition spread between 100 K and 153 K was indicated. From the 57Fe Mössbauer spectra measured in the temperature range of 4.2–300 K, the hyperfine parameters for one tetrahedral and three octahedral sites of ε-Fe2O3 structure were identified. The in-field spectra in the external magnetic fields up to 6 T were taken both above and below the indicated two-step magnetic transition. Their dependence on temperature and external magnetic field suggests that the first step in the temperature range of 153 K–130 K is related to the spin reorientation of the local magnetic moments in the magnetic sublattices and the second step in temperatures 130 K–100 K may be associated with the intermediate spin–high spin state transition of Fe3+ cation in the tetrahedral sublattice expressed in the change of the hyperfine magnetic field.

Spin Seebeck effect in ɛ-Fe2O3 thin films with high coercive field

“…0.4 • for all thin films, see 1. The c-lattice parameters of ε-Fe 2 O 3 samples, 9.462(1)Å (70 nm) and 9.456(1)Å (40 nm), calculated using cos θ/ tan θ extrapolation to correct a possible off-centre position of the film during XRD measurement, are in good agreement with literature values for ε-Fe 2 O 3[11,24]. The stoichiometry of Al-substituted layer was determined as x = 0.30(2) by XRF.…”

“…The material is * corresponding author: knizek@fzu.cz ferrimagnetic at room temperature, with relatively low remanence ∼8 emu/cm 3 and saturation magnetization ∼17 emu/cm 3 , and giant coercive field ∼20 kOe ascribed to its high magnetocrystalline anisotropy [7,8], which can enhanced up to 31 kOe by Rh doping [9]. It undergoes a transition to the paramagnetic state at T C ∼490 K, and a two step magnetic transition in the temperature range 100 − 150 K accompanied by a decrease in coercive field [8,10,11]. The magnetization can be enhanced by a substitution of non-magnetic cation, e.g.…”

Nanometer-size hard magnetic ferrite exhibiting high optical-transparency and nonlinear optical-magnetoelectric effect

“…In addition, development of an optically transparent magnet is highly desirable for new applications, such as transparent electromagnetic wave-absorbing windows or magnetic color pigments for printers. In light of the above requirements, epsilon iron oxide ε-Fe 2 O 3 is an attractive material because it exhibits a large H c value at room temperature71819202122232425. In the present work, we develop a synthetic method for the preparation of single-nanosize ε-Fe 2 O 3 spherical particles.…”

ChemInform Abstract: Multimetal‐Substituted Epsilon‐Iron Oxide ε‐Ga0.31Ti0.05Co0.05 Fe1.59O3 for Next‐Generation Magnetic Recording Tape in the Big‐Data Era.

“…[6][7][8] Magnetic recording tapes are now used for data archiving in insurance companies,b anks,b roadcasters,a nd web services. [10][11][12][13][14][15][16][17][18][19][20][21][22] In such ah igh H c ferrite magnet, the particle size can be downsized because the superparamagnetic limitation size (d s )i sv ery small (i.e., d s is 7.5 nm). Recently,b arium ferrite has also started to be used.…”