Magnetite (Fe₃O₄): a new variant of relaxor multiferroic?

Abstract

The electric polarization, dielectric permittivity, magnetoelectric effect, heat capacity, magnetization and ac susceptibility of magnetite films and polycrystals were investigated. The electric polarization of magnetite films with saturation values between 4 and 8 μC cm(-2) was found to vanish between 32 and 38 K, but in polycrystals no phase transition was detected in this range by heat capacity. Both types of samples showed magnetoelectric effects at low temperatures below a frequency-dependent crossover. This is interpreted as arising from multiferroic relaxor behavior.

Pyroelectric detection of spontaneous polarization in magnetite thin films

“…(d) shows that the dielectric relaxation is thermally activated with E a = 26.8 meV, which is close to the reported values for bulk and film Fe 3 O 4 [16][17][18]52,53. Linear extrapolation yields a prefactor value of τ 0 = 1.64 ns, corresponding to a rather low attempt frequency of less than 100 MHz.…”

“…A strong dielectric dispersion is visible, with a drop of the dielectric constant at temperatures below 50 K, consistent with previous reports. [16][17][18]52,53 The phase response shown in Fig. 3(c) was measured at a chopping rate of 35 Hz.…”

“…32 It is clear that in such materials there is a relationship between the pattern of charge ordering and polarization. However, there is still a discrepancy in the Fe 3 O 4 experimental results, since spontaneous polarization has only been observed well below the Verwey transition point, [9][10][11][12][13][14][15][16][17][18] while x-ray and neutron diffraction studies suggest that the charge-ordered state responsible for the ferroelectricity appears at the Verwey transition and is unchanged upon further cooling. 24,26,28,29 One possible reason for this discrepancy is the high leakage current of Fe 3 O 4 crystals just below the charge-ordering temperature of 120 K.…”

Dielectric and piezoelectric augmentation in self-poled magnetic Fe3O4/poly(vinylidene fluoride) composite nanogenerators

“…4 holds a ferrimagnetic alignment of magnetic dipoles, due to coexistence of an antiferromagnetic superexchange interaction and a predominant ferromagnetic double-exchange interaction between particular cationic coordinations through the overlapping oxygen orbitals [37,38]. As the crystallite size decreases below 30 nm, thermal fluctuations play a major role to develop a superparamagnetic response.…”

Magnetically disordered phase in epitaxial iron-deficientFe3O4thin films

“…The moments on the octahedral and tetrahedral sites interact antiferromagnetically, giving rise to ferrimagnetism with a magnetic critical temperature (T c ) of 858 K [1]. In addition to its magnetic properties, Fe 3 O 4 has also * Corresponding author: moyerja@illinois.edu been well studied for its so-called Verwey transition (T V ) [39], which is a structural and charge-ordering transition around 122 K that is characterized by a change in crystal structure from cubic to monoclinic and an increase in resistivity by over two orders of magnitude [40][41][42][43][44], and more recently, for reports of multiferroicity below T V [45][46][47].…”