Magnetodielectric effect of Bi₆Fe₂Ti₃O₁₈film under an ultra-low magnetic field

Abstract

Good quality and fine grain Bi 6 Fe 2 Ti 3 O 18 magnetic ferroelectric films with single-phase layered perovskite structure have been successfully prepared via metal organic decomposition (MOD) method. Results of low-temperature magnetocapacitance measurements reveal that an ultra-low magnetic field of 10 Oe can produce a nontrivial magnetodielectric (MD) response in zero-field-cooling condition, and the relative variation of dielectric constants in magnetic field is positive, i.e., [ε r (H)-ε r (0)]/ε r (0)=0.05, when T<55K, but negative with a maximum of [ε r (H)-ε r (0)]/ε r (0)=-0.14 when 55K<T<190K. The magnetodielectric effect appears a sign change at 55K, which is due to transition from antiferromagnetic to weak ferromagnetic; and vanishes abruptly around 190K, which is thought to be associated with order-disorder transition of iron ion at B site of perovskite structures. The ultra-low-field magnetodielectric behaviour of Bi 6 Fe 2 Ti 3 O 18 film has been discussed in the light of quasi-two-dimension unique nature of local spin order in ferroelectric film. Our results allow expectation on low-cost applications of detectors and switches for extremely weak magnetic fields in a wide temperature range 55K-190K.

Comparison of room-temperature multiferroics in Bi4Fe2TiO12 film and bulk

“…The clear peak of Bi 4 Fe 2 TiO 12 film at about 50 K in Fig. 3 implies a transition from antiferromagnetism to weak ferromagnetism when warming, as indicated in another publication [7]. Fig.…”

“…X-ray diffraction profiles reveal similar single-phase crystalline nature and random orientation of the two but X-ray photoelectron spectroscopy experiments indicate 1.4 eV lower binding energy of core-state O 1s in film relative to those of bulk, so the improvement of multiferroics in film are attributed to the oxygen vacancies and high fraction of interface. The results have promising applications in multifunctional integrated devices.Multiferroics has become one of the time-honored issues in last years, herepolarization and spin order coexistent simultaneously in one entity [1][2][3][4][5][6][7].Considerable progresses in single-phase materials include direct manipulation of polarization reversal by magnetical field in single crystal TbMn 2 O 5 [1], giant magnetodielectric in single-crystal DyMnO 3 [2], and colossal magnetodielectric effects in single-crystal CdCr 2 S 4 [3]. However, so far, such strong multiferroic couplings have never been discovered in room temperature, although room-temperature strong coupling between magnetic field and polarization has recently reported in LuFe 2 O 4 single crystal, where dielectric constant can transiently decreases by only 20% [4].…”

Magnetic Field‐Induced Ferroelectric Switching in Multiferroic Aurivillius Phase Thin Films at Room Temperature

“…It is most likely that a significant part of the parent B6TFMO phase has (Fig. 9(b)) is thus non-monotonic in nature due to the influence of a proportion of grains behaving as would be expected from the unmodified parent antiferromagnetic B6TFO phase 87,88 . In the magnetic hysteresis loop measurement (Fig.…”

“…By contrast, high-spin Fe 3+ possesses 2 unpaired electrons in its e g orbitals. The parent compound, B6TFO has been reported 59,87,88 to be antiferromagnetic with a magnetic transition to weak ferromagnetism below 65K. The mechanism involving ligand orbitals to facilitate coupling between metal electrons is referred to as super-exchange.…”

Novel Approaches for Genuine Single‐Phase Room Temperature Magnetoelectric Multiferroics

“…A qualitative explanation of the non-monotonic behaviour of the FC curve for B6TFMO was described. 2 Most likely, a significant part of the parent B6TFMO phase was modified to become ferromagnetic at the nanoscale, with the remainder being antiferromagnetic in the same way as in the case of unmodified B6TFO 92,111,129,130 . The variation of magnetization of B6TFMO as a function of temperature (Fig.…”