Enhanced magnetic and room temperature intrinsic magnetodielectric effect in Mn modified Ba₂Mg₂Fe₁₂O₂₂ Y-type hexaferrite

Abstract

We have reported a systematic investigation on structural, magnetic, magnetodielectric and magnetoimpedance characteristics of Y-type Ba 2 Mg 2 (Fe 1−x Mn x ) 12 O 22 (0 ⩽ x ⩽ 0.12) hexaferrite synthesized by solid-state reaction route. Rietveld refinement of x-ray diffraction pattern confirms the phase purity of all the samples with rhombohedral crystal structure. The Mn dopant modulates not only superexchange angle near to the boundary of magnetic blocks but also magnetic transition temperature. Temperature-dependent magnetization data suggests that due to Mn doping at Fe sites, ferrimagnetic to proper screw transition temperature (T II ) increases from 190 K to 208 K, while there is a decrease in proper screw to longitudinal conical spin transition temperature (T I ) from 35 K to 25 K. We observe remarkable decrease in the magnetic field from 20 kOe to 12 kOe to produce intermediate spin ordering from ferrimagnetic ordering which can be understood because of modification of superexchange angle due to Mn doping. The value of loss tangent decreases with increasing doping concentration at 300K, i.e. ~60% and 180% in BMFM4 (x = 0.04) and BMFM8 (x = 0.08) respectively as compared to BMF, suggesting the evolution of intrinsic feature in the doped samples. Magnetodielectric (MD) effect shows that in the low-frequency regime, the robust MD effect is because of Maxwell-Wagner interfacial polarization, whereas in the high-frequency regime intrinsic effect dominates. Further, magnetoimpedance measurement confirms the presence of substantial intrinsic MD% (~6%) at 1.3 T applied field at 300 K for 4% Mn-doped sample. Finally, the nature and strength of magnetoelectric coupling in BMFM4 and BMFM8 samples at 300 K is found to be biquadratic (P 2 M 2 ) and maximum strength of coupling is 3.09 × 10 −4 emu 2 g −2 and 2.34 × 10 −4 emu 2 g −2 , respectively.

Phase Transitions in Magneto-Electric Hexaferrites

“…The classical ceramic technology is the most popular method for preparation of complex polycrystalline oxides. A large amount of research effort has been focused on the preparation of single-phase Y-type hexaferrites. − In summary, the technique is based on a solid-state reaction of alkaline earth carbonates with metal oxides. The powders are homogenized by ball-milling and, after palletization, are synthesized at a high temperature in the 1100–1200 °C range to obtain single-phase Y-type hexaferrite.…”

“…Abdullah et al investigated the Sr substitution effect in the Ba 2– x Sr x Mg 2 Fe 11.48 Mn 0.52 O 22 (0 < x ≤ 1) hexaferrite and found that the Sr substitution raises the spin ordering transition temperature from a proper screw state to a longitudinal conical spin state from 52 to 73 K and from a ferrimagnetic state to a proper screw state, from 210 to 315 K in a 100 Oe magnetic field. In another study, they found that Mn doping at Fe sites raises the transformation temperature from a ferrimagnetic state to a proper screw state from 190 to 208 K, while a drop was seen in the proper screw to longitudinal conical spin transformation temperature from 35 to 25 K in Ba 2 Mg 2 (Fe 1–x Mn x ) 12 O 22 in a magnetic field of 100 Oe.…”

“…Kim et al52 explored the magnetic parameters of the Ba 2−x Sr x Ni 2 (Fe 1−y Al y ) 12 O 22 system and observed a step-like behavior in the initial magnetization plot at 295 K only for the Ba 0.5 Sr 1.5 Ni 2 (Fe 0.97 Al 0.03 ) 12 O 22 sample corresponding to the magnetic phase transition related to the conical spin state. Abdullah et al21 observed a step-like behavior at 5 K and a lower magnetic field in Ba 2 Mg 2 (Fe 1−x Mn x ) 12 O 22 powders. At magnetic fields above 400 Oe, the Ba 2 Mg 2 (Fe 1−x Mn x ) 12 O 22 powders exhibit few intermediate phases (I, II, and III) and a collinear ferrimagnetic phase at magnetic fields near 22 kOe.…”