Ferroelectric order associated with ordered occupancy at the octahedral site of the inverse spinel structure of multiferroicNiFe2O4

Abstract

We report a ferroelectric order at ∼ 98 K for NiFe2O4, which carries an inverse spinel structure with a centrosymmetric F d3m structure at room temperature. The value of spontaneous electric polarization is considerably high as ∼ 0.29 µC/cm 2 for 5 kV/cm poling field. The electric polarization decreases considerably (∼ 17 %) around liquid nitrogen temperature upon application of 50 kOe field, proposing a significant magnetoelectric coupling. The synchrotron diffraction studies confirm a structural transition at ∼ 98 K to a noncentrosymmetric structure of P 4122 space group. The occurrence of polar order is associated with an ordered occupancy of Ni and Fe atoms at the octahedral sites of the P 4122 structure, instead of random occupancies at the octahedral site of the inverse spinel structure. The results propose that NiFe2O4 is a new type-II multiferroic material.

Tuning of multiferroic order with Co doping in CuCr2O4 : Interplay between structure and orbital order

“…6(f)-6(j). The reversal of P(T ) due to a change in sign of E (±5 kV/cm) signifies the ferroelectric order [34][35][36][37]. The P values increase with E , pointing to the fact that the P does not saturate for E at −5 kV/cm for x = 0, 0.6, and 0.8.…”

Room‐temperature multiferroicity in NiFe2O4 and its magnetoelectric coupling intensified through defect engineering

“…Fe ions in NFO0 are distributed in O h as a mixture of Fe 2+ and Fe 3+ and in T d only as Fe 3+ . 42 Both spectra appear to be practically identical, except for a slight systematic shift of the entire profile in NFO20 toward a higher energy. 43 The difference between NFO0 and NFO20 in terms of their XAS spectra becomes more straightforward in their response to an external magnetic field, represented by the X-ray magnetic circular dichroism (XMCD) profile shown in Figure S1; the intentional Fe 2 O 3 deficiency reduces the amount of Fe ions dominantly at T d .…”

“…In fact, this ME coupling at room temperature has yet to be identified, although the existence of ferroelectricity at a fairly low temperature of 98 K was recently reported. 42 By contrast, with the intentional elimination of Fe 2 O 3 from the stoichiometric quantity, the ME coefficient increases rapidly from 0.05 mV/ Oe•cm of the stoichiometric NFO, peaking with 0.18 mV/ Oe•cm at x = 0.2 before it decreases to 0.09 mV/Oe•cm at x = 0.3 (Figure 4B).…”

“…[7][8][9]40,41 The chemical and volume changes that accompany ceramization of the polymer during pyrolysis have been documented in several studies. For example, see Refs [39][40][41][42]. Pyrolysis of polycarbosilane polymer has been modeled by Key et al 43 Ideally, the available individual models for polymer infiltration and pyrolysis should be combined to construct a model for the PIP process.…”

Rhombohedral distortion-driven ferroelectric order and exchange bias effect in geometrically frustrated ZnFe2O4

“…For example, the solely Asite magnetic atom in the spinel structure gives rise to exotic effects such as spin dimerization [1], spin liquid ground states [2][3][4], and suppressed antiferromagnetic order [5], which are often regulated by either orbital ordering or geometric magnetic frustrations, or both. Transition elements in both the Aand B-sites reduce the magnetic frustration, but this produces interesting consequences such as structural instabilities [6][7][8], intricate magnetic structures [9,10], ferroelectricity [11][12][13][14], etc. The solely B-site magnetic atom in AB 2 X 4 is found to have potential for the pyrochlore structure, producing strong geometric magnetic frustration [15,16].…”