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From a batch of lithium-rich highly ordered single crystals of lithium ferrite, a group of 13 spheres were prepared using regions selected for low defect concentrations. Linewidths measured at 5.1 GHz and ∼300°K ranged from 0.87 to 2.06 Oe with a mean value of 1.35 Oe. The resistivity of the crystals was 3 Ω·cm and 4πMs was 3720±50 G. The narrow linewidths in the presence of such high conductivity suggests a conductivity mechanism other than the usual one involving Fe2+ ions. The sphere with the lowest ΔH was used to measure the temperature dependence of ΔH, ΔHk→0 and HA[111] between 4.2° and 300°K at 10.4 GHz. The ΔH ranged from 1.45 Oe at 300°K to 0.55 Oe at 4.2°K with a peak of 2 Oe near 30°K. At 250°K, ΔHk→0 was 0.4 Oe. It exhibited a peak near 30°K (whose maximum was not measured) and was only 0.06 Oe at 4.2°K. The anisotropy field HA[111] decreased monotonically from 625 G at 4.2°K to 390 G at 300°K. The possession of samples having very small linewidths permitted the study of the effect of ordering on the room-temperature linewidth uncomplicated by other effects.

Articles you may be interested inFrequency and temperature dependence of the ferromagnetic resonance linewidth in single crystal platelets and pulsed laser deposited films of barium ferrite Angle dependence of the ferromagnetic resonance linewidth in easy-axis and easy-plane single crystal hexagonal ferrite disks J. Appl. Phys. 81, 7458 (1997); 10.1063/1.365288Frequency dependence of the ferromagnetic resonance and effective linewidth in single crystal manganese doped barium ferrite (abstract) Frequency dependence of the ferromagnetic resonance linewidth and effective linewidth in maganese substituted single crystal barium ferrite Submicroscopic defects have been established as the major cause of linewidth in lithium ferrite single crystals. Over 100 highly polished lithium ferrite spheres showing no microscopic defects exhibited AHs ranging from 2 to 60 Oe. Spheres of low AH and high AH were chemically polished and etched. Low AH spheres had very few pits; high AH spheres were severely mottled and etched. X-ray topography and etching of (111) plates have confirmed that regions with defects > 10 5 cm-2 exist near regions of only 10 2 cm-2 • The regions are often separated by a sharp boundary along (110 >.Spheres prepared from very low-pit-count material repeatedly had AHs of <2 Oe before heat treatment. The defects appear to be dislocations and compositional variations. Heat treatment at 850°C caused no observable change in x-ray topographs. By careful selection of the crystals of low defect content, AHs as low as 0.87 Oe at 5.1 GHz and 25°C have been observed.

Ferrimagnetic resonance linewidths as low as 2.6 oe can be obtained in lithium ferrite spheres at room temperature and 5 kMc by a series of treatments including polishing, heat treatment at 800°C, addition of lithium, and ordering. There exist optimum times of processing for each crystal. Freshly grown crystals show unusual variations in linewidth with processing, and this behavior is tentatively explained on the basis of strains in the crystal and nonuniformity of lithium content within the spherical sample.

The saturation magnetization, Curie temperature, compensation point, and ferromagnetic resonance linewidth of Y3Fe5−xMxO12, M=Ga or Al, depend upon the thermal history of the sample. For example, a single crystal of YGaIG, x=1.26, will exhibit a room-temperature 4πMs between 220 and 88 G as it is quenched from temperatures ranging downward from 1275°C and finally slow-cooled to room temperature. Tc will decrease 3.5°C. The results can be explained by assuming the Ga or Al concentration on octahedral sites increases with increasing temperature. The direction of the change in Curie temperature is predicted by Gilleo's theory. The results are important to the control of magnetic properties of garnets in applications requiring closely matched samples.