The effect of Zn-Nb substitution on magnetic properties of strontium hexaferrite nanoparticles

We have studied the crystal structure, magnetic properties and temperature coefficient of coercivity of Sr(Zn0.7Nb0.3)(x)Fe12-xO19 strontium hexaferrite nanoparticles, fabricated using a sol-gel technique for perpendicular magnetic recording. X-ray diffraction analysis has shown that the strontium hexaferrite with small substitutions still remains in a hexagonal magnetoplumbite phase. Magnetic measurements have revealed that the values of specific saturation magnetization, MS, increased to 67-73.3 emu/g (x = 0-0.8), while coercivity, H-c, is reduced from 6.5 to about 2.3 kOe. It indicates that saturation magnetization and coercivity of strontium hexaferrite particles can be maintained over a very wide range by an appropriate amount of Zn-Nb doping contents. Moreover, temperature measurements have exhibited that Zn-Nb substitution can effectively decrease the temperature coefficient of dH(c)/dT with the increase in doping, which means that the samples have a perfect thermal stability. Also, it has been found that coercivity has a small positive temperature coefficient as compared with the intrinsic ones, which may be understood by the changes of both non-collinear magnetic structure and local spin canting when Zn-Nb doping increases. (C) 2003 Elsevier B.V. All rights reserved.