Determination of anisotropy field in polycrystalline lithium ferrites from FMR linewidths

Abstract

A technique for separating anisotropy and porosity induced FMR line-broadening contributions in narrow linewidth polycrystals has been extended to large linewidth lithium ferrite materials. The FMR linewidth is measured versus frequency and temperature T. Since the porosity contribution is proportional to the magnetization 4πMs, and the anisotropy field Ha falls off much faster at high T than does 4πMs, the two contributions to the linebroadening can be separated. Three samples were studied: Li-ferrite with and without cobalt addition (0.01 Co atoms/formula unit), and a Li-ferrite with 0.01 Co and 0.26 Ti at./f.u. The anisotropy field for unsubstituted Li-ferrite was found to decrease monotonically with T with Ha≊ 350 Oe at 25 °C, in agreement with single crystal data. Cobalt addition was found to decrease the room temperature Ha in the Li-ferrite without titanium but not in the Li-Ti-ferrite. This agrees with previous observations of Ti decreasing the effectiveness of Co in reducing the anisotropy.

Gilbert damping constant in polycrystalline CO2MnSi Heusler alloy films

“…For polycrystalline films, a is large compared with those of single crystals [6] and almost independent of the annealing temperature. The large a-value can arise from inhomogeneity of porosity [7][8][9]. This is because the pores at the grain boundary cause the non-uniformity in the internal magnetizing field or nonuniform demagnetizing field due to the internal defect.…”

Enhanced ferromagnetic properties of low temperature sintering LiZnTi ferrites with Li2O–B2O3–SiO2–CaO–Al2O3 glass addition

“…In these investigated samples, the anisotropy field H a ranged from about 260-315 Oe. Compared with the anisotropy field H a at 25°C (375 Oe) of single crystal of pure lithium ferrite obtained by Brower and Patton [33], H a displayed the expected decrease mainly due to the introduction of Zn 2+ ions. As can be seen from Fig.…”

“…In order to explain the influence mechanism of DH, an approximate calculation for the separation of DH has been done by adopting dipolar narrowing theory [31]. Compared to DH a or DH p , DH i values are small and could be neglected [7,32,33]. Thus we considered DH a and DH p for the line broadening contributions in this work.…”

Anisotropy and Relaxation Effects of Co2+ Ions in LiTi Ferrite.

“…These effects were also seen in the recent work by Brower and Patton [4]. The interpretation of this unexpected phenomenon will be analyzed in a new model to be introduced in a later section, but for the moment it 4+ is sufficient to assume that Ti ions serve to disrupt the nor-2+ mally strong positive anisotropy contributions from Co in these 2 materials.…”

“…However, it is principally in the lithium ferrite family 13,4] and to a lesser extent in the garnet lattice [14), the explanation of these catastrophic effects on the hysteresis loop was based on the role of anisotropy in creating reverse domains at or near the remanent state. These results suggested that the concentrations of Co 2 + in lithium ferrite would have a practical upper limit determined by xc, the concentration value for anisotropy cancellation.…”