摘要:

As part of an effort to understand the nature of the transition responsible for the very strong absorption band edge and the large magneto‐optical effects in ferric ion containing ferro‐ and ferrimagnets, the optical and magneto‐optical properties of erbium orthoferrites (ErFeO3, &THgr;N= 620°K for Fe+3spins) have been examined by reflection techniques. Ellipsometer and Kerr rotation measurements were made on growth surfaces (cplane) at room temperature over the visible spectrum. The real and imaginary parts of the dielectric constant show two bands at 22 000 and 26 000 cm−1, with oscillator strengths of 0.03 and 0.4, respectively. The normal incidence polar Kerr rotation has a sharp peak of 11.5 min at 23 500 cm−1. There are several weaker structures between 15 000 and 22 000 cm−1which are believed to be due to low‐lying branches of the crystal‐field spectrum of the Fe+3ion. By combining the Kerr rotation and dielectric constant data, the off‐diagonal element of the dielectric permittivity tensor was calculated. The results suggest that the main 26 000 cm−1band and the unresolved 23 500 cm−1band represent the &sgr; and &pgr; processes of the electron transfer transition. They further suggest that the &pgr; process component of the off‐diagonal element has opposite sign relative to that for the &sgr; process and the first allowed internal transition.

ISSN:0021-8979    

DOI:10.1063/1.1714191

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Faraday rotation and absorption measurements were made on a bulk single crystal and on evaporated polycrystalline films of EuSe. Bulk EuSe is ferromagnetic, transparent in the red, and exhibits an unusually large Verdet constant at room temperature: −9.7 min/Oe‐cm at 6660 Å where the absorption is 173 cm−1. Measurements at 77°K show that the Verdet constant varies approximately inversely with temperature and thereby correlates with the magnetic susceptibility. These properties are due to the Eu+ +ion and are comparable to those we have observed in other divalent europium compounds such as Eu2SiO4.The evaporated films of EuSe exhibit a broad but well‐defined absorption band at 4600 Å which is essentially duplicated in similarly prepared films of EuS and EuO at 5200 and 5800 Å, respectively. The wavelength dependence of the Faraday rotation of EuSe exhibits a rather complicated structure with two sign reversals in the region of the absorption band. At 6660 Å the Verdet constant measured at room temperature is −6.3 min/Oe‐cm agreeing in sign and approximately in magnitude with the bulk value, whereas the maximum value of Verdet constant, +25 min/Oe‐cm, occurs at 4330 Å.

ISSN:0021-8979    

DOI:10.1063/1.1714192

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Circulators which can be operated at cryogenic temperatures are discussed. Both symmetrical Y‐junction circulators using polycrystalline ferrimagnetic garnets and hybrid‐gyrator circulators using single crystals are evaluated. The temperature dependence of the ferromagnetic resonance losses of polycrystalline aluminum‐doped and undoped yttrium iron garnet is reported. Device performance is evaluated in terms of the measured material properties.

ISSN:0021-8979    

DOI:10.1063/1.1714193

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

CrI3, noteworthy as one of the few insulating ferromagnets, is one of a series of presumably isomorphous compounds (CrCl3, CrBr3, and CrI3) which show similar or closely related magnetic ordering. CrI3samples containing some single crystals (plates a few square millimeters in area) were made by reacting chromium metal and iodine in a sealed quartz tube. Magnetization measurements of the powder were made by Williams and Sherwood at several fields up to 15 300 Oe over the range 1.5° to 300°K. In addition,M(H) was plotted at 4.2°K up to 70 000 Oe. The ferromagnetic Curie temperature is 68°K, and the paramagnetic Curie temperature is 70°K. The low‐temperature saturation magnetization is 3.10 &mgr;B/Cr+ + +, corresponding to 4&pgr;M= 2690 G. The field for ferromagnetic resonance was measured at 86, 91, and 99 Gc/sec. The spectroscopic splitting factorg= 2.07, and the anisotropy field 2K/M= 28.6 kOe at 1.5°K.Optical transmission measurements on CrI3single crystals showed a very strong absorption band down to a band edge near 10 000 cm−1. The specific magnetic rotations associated with the band edge are almost as large as those observed in the tribromide. Evidence of domain diffraction was seen.

ISSN:0021-8979    

DOI:10.1063/1.1714194

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Hall coefficients and resistivity have been measured over the temperature range 77° to 300°K on polycrystalline MnBi films prepared with thecaxis of the crystallites normal as well as parallel to the plane of the film. The Hall resistivity follows the well‐known relation&rgr;H=R0H+MR1, whereR0andR1are the ordinary and extraordinary Hall coefficients andMis the magnetization. At room temperature,R0is 6×10−3cm3/C for both types of films andR1is 7×10−2and 2.5×10−1cm3/C for the perpendicular and parallel films, respectively.Measurements of the magneto‐optic Faraday rotation of perpendicular films indicate that the Faraday rotation is directly proportional to the magnetization. Over the visible wavelength region, the Faraday rotation was found to increase as temperature decreases from 300° to 87°K, by a factor less than 25%. The specific rotation for a typical magnetically saturated film was 1.4×105deg/cm at the 6328‐Å He&sngbnd;Ne laser line at room temperature.Our measurements are in agreement with Goodenough's suggestion of metallic conductivity resulting from adband formed from the transition metal cations with the assistance of large numbers of interstitial cations. An effective hole density of 1021cm−3and Hall mobility of approximately 10 cm2/V‐sec characterize these films.

ISSN:0021-8979    

DOI:10.1063/1.1714195

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Materials from the garnet family 3[(1‐x) Y2O3·xGd2O3]· 5[wAl2O3· (1‐w) Fe2O3] have been investigated for use in latching‐type digital phase shifters. At room temperature, asxandwvaried from 0 to 0.30, the electrical properties of these materials varied in the following manner: saturation magnetization (4&pgr;Ms)−1780 to 500 G, resonance linewidth (&Dgr;H)−33 to 200 Oe, remanence ratioRr(Br/Bs)−0.90 to 0.65, coercive force (Hc)−0.50 to 2.00 Oe, switching constant (Sw)−0.50 to 1.00 &mgr;sec‐Oe. By proper choice ofxandw, some of these properties can be made quite insensitive to temperature and power variations over wide ranges. It was found that, althoughHcandRrtend to undergo large unfavorable changes withxandw, they could be controlled by increasing the average size of the crystallites. A five‐bit (180°, 90°, 45°, 22½°, and 11¼°) phase shifter was developed using material from the above family in a square toroid geometry. This device operated across the frequency band 5.4 to 5.9 Gc/sec with a switching rate of 5 kc/sec and a maximum switching time of 1 &mgr;sec. Phase‐shift stability over the temperature range 50° to 125°F was better than 5%, losses were less than 0.80 dB and VSWR less than 1.25 across the frequency range. The unit performed equally well at peak power levels up to 10 kW and average power levels up to 300 W. The total energy required for continuous switching of the 180° bit at the above rates was slightly over 200 &mgr;J.

ISSN:0021-8979    

DOI:10.1063/1.1714196

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

If the rf and dc magnetic fields are parallel, the absorption coefficient &mgr;″ at low power levels is theoretically expected (for YIG at room temperature, a frequency of 10 Gc/sec, and a dc field of 1 kOe) to be of the order of 2×10−4. We have calculated how the steady‐state absorption varies with dc and rf field strength below the instability threshold. Experiments on a high‐purity YIG single crystal are in reasonably good agreement with the theoretical expectations.

ISSN:0021-8979    

DOI:10.1063/1.1714197

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A new magnetoelastic resonance effect is described. A dc magnetic field was applied in the long direction of YIG slabs (1 cm long, 0.5 cm wide, and 0.1 or 0.07 cm high), each end of which was inserted in a stripline cavity. Under appropriate conditions a pulse of microwave power applied to one cavity resulted in a pulse in the second cavity delayed by several microseconds. Small variations were observed in the amplitude of the delayed pulse as the dc field was varied. Similar variations with the same periodicity (∼1 Oe) were also observed in the undelayed reflection from the input cavity. The amplitude variation is attributed to the excitation of magnetoelastic resonances in the nonuniform magnetic field near the endface of the sample. Because of the strong coupling between spin waves and elastic waves, the turning point (at whichkspin waves=0) and the endface of the sample define a magnetoelastic quasicavity whose resonances give rise to the effect noted. According to this interpretation the separation of adjacent peaks should be &dgr;H= |H′dem|&lgr;/2, whereH′demis the gradient of the demagnetizing field evaluated at the crossover point (kspin wave=kphonon) and &lgr; the wavelength of transverse elastic waves. Measurements have been made showing the dependence on dc field, slab thickness, and frequency. Agreement with theory is satisfactory.

ISSN:0021-8979    

DOI:10.1063/1.1714198

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Direct spectroscopic evidence has been obtained of microwave sidebands imposed on a monochromatic light beam by transmission through a single crystal of chromium tribromide at ferromagnetic resonance. Microwave frequencies above 13.5 Gc/sec may be used, and the most favorable optical wavelengths for this effect lie between 4750 and 5000 Å. This work has demonstrated modulation of a 4810‐Å beam by a 23.5‐Gc/sec microwave signal. This paper discusses the conditions under which the modulation may be observed, and how some of these may be optimized.

ISSN:0021-8979    

DOI:10.1063/1.1714199

出版商:AIP    

年代:1965

数据来源: AIP