Structural and magnetic properties of Cu-V substituted M-type barium hexaferrites

In search of magnetic materials with improved magnetic characteristics for practical applications, M-type barium hexaferrites with Fe³⁺ ions partially substituted by a mixture of Cu and V ions were prepared by ball milling and sintering at 1200° C. The structural analyses of the prepared BaFe_12-2xCu_xV_xO₁₉ samples (x = 0.1, 0.2, 0.3, 0.4) revealed the presence of BaM phase, in addition to α-Fe₂O₃, Ba₃V₂O₈, and BaFe₂O₄ nonmagnetic phases which evolved as x increased. Scanning electron microscopy (SEM) imaging demonstrated the presence of different phases in the substituted samples, and a general trend of particle-size growth with increasing x. Energy dispersive spectroscopy was used to examine the local stoichiometry of the samples, and confirmed the different phases identified by XRD analysis. The saturation magnetization was found to be high for low substitution level (72 emu/g for the sample with x = 0.1 sintered for 2 h, and 65 emu/g for the sample sintered for 10 h), while it decreased significantly with increasing the substitution level. The coercivity (H_c) for the samples sintered for 2 h was found to decrease sharply with increasing x, even at low substitution levels (x < 0.2), where it decreased from about 3.5 kOe for the un-substituted sample down to about 1.6 kOe for the sample with x = 0.1, and down to below 0.3 kOe at higher substitution levels. The coercivity of the sample with x = 0.1 sintered for 10 h reduced further, down to about 677 Oe, demonstrating properties demanded for magnetic recording applications. Further, washing with HCl was found to remove some of the nonmagnetic phases, and increase the yield of the BaM phase. (paper)