摘要:

It is shown that the simple ferrite spinels (M2+Fe2O4) crystallize readily from the ternary flux system MO&sngbnd;Na2O&sngbnd;Fe2O3. The liquidus‐solidus phase diagrams for the pseudobinary of Na2Fe2O4&sngbnd;CoFe2O4and the ternary Na2O&sngbnd;CoO&sngbnd;Fe2O3are presented. A general discussion of flux growth of ferrite crystals of both the simple spinel type and the more complex layered structures (BaFe12O19) is given. Crystals of CoFe2O4were grown from a mixture of 1.5 moles of CoFe2O4and 1 mole of Na2Fe2O4by utilizing a platinum wire cold finger.

ISSN:0021-8979    

DOI:10.1063/1.1728733

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A series of uniaxial materials has been prepared and studied in which the effective anisotropy field can be controlled and varied over the range of 0 to 12 700 oe. The materials are solid solutions of the NiW and CoW compounds and have the chemical formula BaO·2[Ni1−xCoxO]·7.8Fe2O3withxvarying from zero, where the anisotropy field is 12 700 oe, to 0.5 where the anisotropy field is vanishingly small. The temperature dependence of the net resultant anisotropy field, linewidth, andgfactor of these materials is discussed. By using oriented polycrystalline samples of these materials, the effective internal anisotropy field can be used to augument external applied fields. Different materials of this series have been used to construct resonance isolators atV‐ andK‐band frequencies with bandwidths of the order of 20% and peak isolation ratios of greater than 30 to 1.

ISSN:0021-8979    

DOI:10.1063/1.1728734

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Single crystal (ZnY) (Ba2Zn2Fe12O22) was used in an investigation of the variation of the magnetic susceptibility with microwave magnetic field. The large anisotropy field in these materials makes them attractive for applications in microwave devices. Measurements were made in the frequency range of 8.6 to 37.7 kMc. The microwave magnetic field in the cavities extended up to 35 oe. Measurements taken at a constant frequency indicate that there is an appreciable shift in the field required for resonance as a function of power. This shift in the resonance field is superimposed on the usual decline of the main resonance. Measurements indicate that the shift effect of the resonance field decreases as the linewidth and frequency are increased. In the frequency range of 8.6 to 16.6 kMc, the critical field increases with frequency. Above this frequency, the critical field tends to decrease. AtX‐band frequencies, the critical field compares favorably with that of YIG material.

ISSN:0021-8979    

DOI:10.1063/1.1728735

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A new nickel ferrite has been developed which contains simultaneously aluminum and gallium. Compositions have been prepared according to the formula NiAlyGaxFe2−(x+y)O4. The total substitutions of gallium and aluminum have been varied from 0 to 1.2. Several ratios of aluminum to gallium have been made. The unique feature of this system is that since the gallium substitutes in the tetrahedral sites and aluminum in the octrahedral sites, the compensation point normally associated with nickel aluminum spinels can be shifted to much higher nonmagnetic ion substitutions. There exists a composition for which there is no compensation point. Measurements of saturation magnetization, Curie temperature, linewidth, andgefffactor have been made. AC‐band circulator‐switch using one of these materials has been constructed and successfully tested at 75‐kw peak power with a 0.001 duty cycle. This device was also successfully tested at a power level of 475 w cw in an ambient temperature of 85°C.

ISSN:0021-8979    

DOI:10.1063/1.1728736

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Subsidiary absorption measurements on polycrystalline yttrium aluminum iron garnet and nickel aluminum ferrite yield values of &Dgr;Hkwhich are the order of several oersteds. These spin wave linewidths appear to be independent of aluminum content. At power levels several db in excess of the power level for the onset of subsidiary absorption, a power dependent zero field loss has been found.

ISSN:0021-8979    

DOI:10.1063/1.1728737

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The magnetic and microwave properties of polycrystalline garnets of the Gd3−xYxFe5−yAlyO12type were investigated. Compositions of low magnetization (∼600 gauss) and narrow linewidth (∼125 oe) were found which are suitable for operation in devices where temperature compensation is required.

ISSN:0021-8979    

DOI:10.1063/1.1728738

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Temperature stability of the magnetization of microwave garnet materials is very desirable provided in obtaining this stability the linewidth,gfactor, and Curie temperature of the material are still suitable for microwave applications. Most rare‐earth garnets possess compensation points in their magnetization vs temperature characteristics. These compensation points when suitably controlled by ionic substitutions can be used to produce microwave garnet materials whose magnetizations are quite temperature independent. The microwave properties of the following compositions have been investigated:3[(1−X−Z)Y2O3·XGd2O3·ZDy2O3]·5[(1−W)Fe2O3·WAl2O3], forX=0 to 1.00,Z=0 to 0.1, andW=0 to 0.1. The magnetizations of these compositions have been studied from −195°C to the Curie temperatures. The compensation points of the magnetization are controlled by varying the rare‐earth and aluminum content of the material. The result is a series of materials possessing magnetizations in the region of 1200 to 300 gauss which vary no more than ±10% over the temperature range of −25° to +125°C. The other associated properties of these compositions are very suitable for microwave applications. The thresholds for nonlinear effects in these materials are relatively high particularly for those compositions containing dysprosium. Many temperature stable microwave components have been developed for high‐power applications using these materials.

ISSN:0021-8979    

DOI:10.1063/1.1728739

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The large magnetic anisotropy field that is encountered in many planar ferrites markedly affects the rf magnetic field at which spin wave instability sets in. When the rf magnetic field is applied perpendicular to the dc field, spin wave instability can occur through the first‐ or second‐order process. At ferromagnetic resonance, the first‐order process dominates if the frequency is smaller than a characteristic frequency &ohgr;c. This characteristic frequency has been calculated for ellipsoidal samples. For most sample shapes, the anisotropy field tends to increase &ohgr;c, thus favoring the occurrence of the first‐order process. In addition, the anisotropy tends to decrease the critical field at which the spin wave instability sets in. Assuming the spin wave relaxation rates to be equal in the two situations compared, we find that the second‐order threshold is reduced (approximately) in the ratio of (8&pgr;M / Ha)½for relatively high frequencies; and in the ratio of (&ohgr;/&ggr;Ha)½for relatively low frequencies. In parallel pumping, the threshold field is reduced in the ratio of 4&pgr;M/ (4&pgr;M+Ha) at low biasing fields.

ISSN:0021-8979    

DOI:10.1063/1.1728740

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

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.

ISSN:0021-8979    

DOI:10.1063/1.1728741

出版商:AIP    

年代:1962

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1728742

出版商:AIP    

年代:1962

数据来源: AIP