Co-Doped Rare-Earth (La, Pr) and Co-Al Substituted M-Type Strontium Hexaferrite: Structural, Magnetic, and Mossbauer Spectroscopy Study

The present study investigates the influence of La3+ and Pr3+ doping on the structural, magnetic properties, and hyperfine fields of Sr0.7RE0.3Fe12-2x CoxAlxO19, (RE: La3+ and Pr3+, x = 0.0 - 0.8) hexaferrite compounds prepared via auto-combustion technique. The XRD analysis shows a linear decrease in a and c lattice and unit cell volume contraction with the content x. The room temperature magnetic study shows that for the Pr3+ doped Sr0.7Pr0.3Fe12-2x CoxAlxO19 (Pr3+-SrM), the magnetization value monotonically decreases while for La3+ doped Sr0.7La0.3Fe12-2xCoxAlxO19 (La3+-SrM) magnetization value shows a noticeable increase in magnetization value with x. The coercivity of the Pr3+-SrM compound was observed to decrease while that of the La3+-SrM compound showed a marked 40% increase at x = 0.2 (~5829 Oe) in comparison to undoped SrFe12O19 (~3918 Oe). A difference in Curie temperature was also observed, with Tc ~ 525°C at x = 0.4 for Pr3+-SrM and Tc = 505°C for x = 0.4 for La3+-SrM compound. The observed differences in magnetic properties have been explained on the basis of the site occupancy of Co2+ and Al3+ in the presence of rare-earth ions. The presence of non-magnetic rare-earth ion, La3+, improved saturation magnetization, and coercivity and deemed suitable replacement for Sr2+. The hyperfine parameters namely quadrupole shift showed a decrease with the La3+ or Pr3+ doping independent of (Co2+-Al3+) ions doping. Overall, the Mossbauer analysis suggests that the (Co2+-Al3+) impurities prefer occupancy at 2a site.

Structural, Magnetic, and Electrical Properties of RE Doped Sr_0.82RE_0.18Fe_12-xAl_xO₁₉(RE = Gd, Pr, Sm) Compound

Among the family of ferrites, M-type hexaferrites has many industrial applications ranging from simple magnets to microwave devices. Improvement in magnetic and dielectric properties of ferrites is of continuous interest. In this present work details study is done to observe the effect of co-doping of rare-earth (RE3+: Pr3+, Sm3+, and Gd3+) and aluminum in Sr0.82RE0.18Fe12-xAlxO19 (x = 0.0, 0.5, 1.0, 1.5, 2.0). The adopted samples were synthesized via autocombustion technique. Detailed synthesis, structural, magnetic, and electrical measurements of samples were performed to understand structural-magnetic-electrical property relationship. The Al3+ substitution for Fe3+ brings in a significant enhancement in coercivity but reduces magnetization due to the magnetic dilution effect. Additional coercivity enhancement was possible with RE3+ doping without affecting the magnetization of samples. Among all RE3+ doped samples, Pr3+ doped samples showed the highest Curie temperature, (Tc ~ 465℃), while Gd3+ doped samples showed little variation in dielectric properties in GHz frequency range. This makes RE3+ doped samples as an ideal candidate for high-frequency microwave applications. Pr3+ with oblate charge distribution (negative Stevens constant) was observed to substitute well into the lattice consequently bringing in desired improvements in physical properties of Sr0.82RE0.18Fe12-xAlxO19 ferrite.