Optical and Multiferroic Properties of Gd‐Co Substituted Barium Hexaferrite

Abstract

This report demonstrates Gd-Co substituted M-type barium hexaferrite, Ba 1-x Gd x Co x Fe 12-x O 19 , successful synthesis adopting sol gel method. Formation of crystalline magneto-plumbite structure and presence of other phases are verified from the X-ray diffraction analysis. Vibrational modes in FT-Raman spectra show the formation of P63/mmc group can be related with magneto-plumbite structure. TEM images of these materials are also discussed. UV-Vis-NIR spectra shows that with material substitution optical energy band gap increases 3.99 eV to 4.28 eV. The observed Fe 3+ ions peak could be correlated to peak line width and occurrence of symmetrical resonance in electron spin resonance (ESR) spectra. The dielectric constant shows high value at low frequency and it becomes constant at high frequency. The retentivity and coercivity of the material decreases with increasing substitution. Multiferroic nature of hexaferrite is analyzed using ferroelectric loops.

Structural, Dielectric, and Magneto‐Optical Properties of Al‐Cr Substituted M‐Type Barium Hexaferrite

“…From UV‐Vis‐NIR spectra (Figure ), the absorption region for hexaferrites has been found to be 200–600 nm. This result is supported by the literature …”

“…Raman modes are observed at 171, 204, 281, 317, 407, 513, 606, and 674 cm −1 . The Raman modes at 171, 204, and 281 cm −1 could be respectively attributed to E 1g , E 1g , and E 2g symmetry corresponding to the vibration of S‐block whereas the Raman modes at 317, 407, 513, 606, and 674 cm −1 corresponds to the vibrations of 12k octahedral site, 12k and 2a octahedral site, 4f 2 octahedral site, 2b bi‐pyramidal site due to of A 1g , E 1g , A 1g , A 1g , and A 1g symmetry, respectively …”

“…To improve the properties of hexaferrite, Fe 3+ ions can be replaced by a cation such as transition metals. Several attempts have been made to modify the magnetic properties of M‐type hexagonal ferrite by the substitution of barium and/or iron sites with divalent or trivalent ions or a combination of divalent and trivalent ions such as Mg‐Ti, Cr‐Ga, Ni, Al‐Mn, Gd‐Co, Mn‐Ti, Co‐Ti, Gd‐Na, Sc‐Mg, La‐Zn . The motivation for this research stems from the fact that Al 3+ substitution result in high dielectric constant as reported by Mahadevan et al Similarly, it has been reported that Cr 3+ substitution at Fe 3+ site could lower the coercivity of hexaferrites, this is vital as high coercivity is not favorable for certain applications such as microwave absorption .…”

Magnetic and dipole moments in indium doped barium hexaferrites

“…2). The Fe 3+ cation in the Fe2 -2b position is Spontaneous polarization was previously observed in diamagnetic doped barium hexaferrites [13][14][15][16][17][18][19][20][21], but the mechanism of its appearance remains unclear. The appearance of a nonzero dipole electric moment, due to the distortion of the oxygen environment of the magnetoactive iron cations, can be a consequence of the order-disorder transition, which is undergoing crystal structure.…”

“…Mechanism for its realization is also important [11][12][13][14]. This question presents both fundamental scientific interest and it is important from a practical point of view [15][16][17][18][19][20][21][22][23][24][25]. Some controversy about ferroelectricity in the M-type hexaferrites exists [26].…”