Study of extrinsic magnetic properties of Mn-Mg-Zn ferrite nanoparticles at liquid nitrogen temperature

Magnetic behaviour of Mn_xMg_0.8–xZn_0.2Fe₂O₄ (0 ≤ x ≤ 0.7 at a step of 0.1) nano ferrites has been explored. From the XRD patterns, the secondary phase of α-Fe₂O₃ is clearly evident in the ferrite compositions for x  ≥ 0.4. The oxygen positional parameter (U) is in the range 0.387 – 0.389 and it is greater than the ideal value of 0.375. The bond angles provided an overview about the insight of magnetic behaviour of present series of ferrite samples. The M-H loops indicate the soft magnetic behaviour of present ferrite systems. For the ferrite composition x = 0.5, the highest value for saturation magnetization (M_s) of 35  and 42 emu/g has been reported at 300  and 80 K. The smaller values of remnant magnetization (M_r) and coercivity (H_c) indicate that the ferrite nanoparticles are single domain structure possessing core–shell morphology. For all values of M_s and M_r at 300 K and 80 K, the ratio of M_r/M_s is less than 0.5 indicating that the ferrite nanoparticles are under strong inter particle interactions. The magnetization-temperature (M-T) graphs revealed that blocking temperature (T_B) is above and nearer to 300 K. The magnetocrystalline anisotropy is a probable factor for the changes in the blocking temperature. The results are interpreted in terms of Y-K interactions, core–shell interactions, secondary phases and magnetocrystalline anisotropy.