Abstract
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.
Highlights
M-types hexagonal ferrites like BaFe12O19 and SrFe12O19 with magnetoplumbite structure have been widely investigated and used as a permanent magnet because of their high magnetization (Ms) and coercivity (Hc), low manufacturing cost for industrial production and stability [1] [2] [3]
The structural, magnetic, and electrical properties of Re3+-Al3+ substitution in Sr0.82RE0.18Fe12−xAlxO19 hexaferrite synthesized via auto-combustion were investigated
The increase in coercivity is attributed to a reduction in grain size leading monodomain grains and change in magnetocrystalline anisotropy
Summary
M-types hexagonal ferrites like BaFe12O19 and SrFe12O19 with magnetoplumbite structure have been widely investigated and used as a permanent magnet because of their high magnetization (Ms) and coercivity (Hc), low manufacturing cost for industrial production and stability [1] [2] [3]. A significant improvement in magnetic properties has been reported in SrFe12O19 hexaferrites by the substitution of Sr2+ by rare-earth (RE3+) ions such as by La3+ [7], Nd3+ [8], Sm3+ [9] [10], Gd3+ [11], Fe3+ ions by magnetic ions such as Co2+ [12] [13] and Cr3+ [14] ions and non-magnetic ions such as Al3+ [15], Zn3+ [16], Ga3+ [17] and Cd3+ [18] [19], and replacement of Sr2+/Fe3+ together with Pr-Zn [20], La-Cu [21], and La-Zn [22] From this reported literature on hexaferrites, it is observed that the insertion of RE3+ into hexaferrite lattice inhibits grain growth, reduces grain size, and controls the coercive force for wide practical applications. The process has the advantages of using inexpensive precursors, and the powders obtained are nanosized and homogeneous as compared to ferrites prepared via traditional solid-state reaction, a process which often leaves secondary phases in the compound [15]
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