摘要:

The electronic magnetization of Eu3+ions at low temperatures is associated with Van Vleck temperature‐independent paramagnetism; the ground state hasJ=0. We have calculated the Faraday rotation for this ion. A contribution from the Van Vleck paramagnetism is partially cancelled by the usual diamagnetic term. The resulting rotation should be observable in Eu3+in the microwave and infrared regions. In the appropriate limits we find for the rotation per unit length&Dgr;&thgr;/&Dgr;x=(48&mgr;B2N/ℏ&ngr;)(ℏ&ohgr;/&Dgr;)4(&mgr;BH0/&Dgr;)[1−(ℏ&ohgr;/&Dgr;)2]−2,whereNis the concentration,vis the velocity of light in the medium, and &Dgr; is the splitting betweenJ=1 andJ=0. We give the appropriate modification of this formula in a crystal field. We calculate the gyromagnetic ratiog′; at low temperatures the calculations of Frank have to be corrected to take into account nuclear effects.

ISSN:0021-8979    

DOI:10.1063/1.1709675

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The far‐infrared spectral response of antiferromagnetic UO2has been studied between 10 and 220 cm−1as a function of temperature, magnetic field, and uniaxial strain. In the ordered state, resonant absorption is observed at 17.5, 79.0, 99.0, 110.5, 184.0, and 216.0 cm−1. The resonances at 79.0 cm−1and 99.0 cm−1are shown to be nondegenerate antiferromagnetic modes. Absorption by zone‐boundary magnons within domain walls is believed responsible for the structure at 17.5 cm−1. The remaining modes appear to be anomalous phonon absorptions which appear in the ordered state by virtue of the strong magnon‐phonon interaction.

ISSN:0021-8979    

DOI:10.1063/1.1709676

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The temperature dependence of Co2+‐ion absorption‐band maxima has been studied in crystals of RbCoF3, KMn0.975Co0.025F3and KNi0.75Co0.25F3. Shifts in the cobalt‐band maxima are superimposed on changes of purely thermal origin. The additional changes in the band maxima are attributed to the magnetic properties of these materials. In pure cobalt salts the magnetically induced changes begin, with decreasing temperature, at the Ne´el temperatures of the materials. Similarly, in salts where the cobalt ion is not a major constituent, the shifts in the Co2+bands appear approximately at the Ne´el temperature of the host.

ISSN:0021-8979    

DOI:10.1063/1.1709677

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The general theory of magneto‐optical effects is reviewed and it is shown that one can describe these phenomena in terms of a macroscopic dielectric tensor by setting &mgr;=1. This is true even when the microscopic origins of the dielectric constant are magnetic‐dipole transitions. For the case of electric‐dipole transitions, the dispersive magneto‐optical effects (i.e., Faraday or Voigt effects) can be interpreted in terms of an effective Hamiltonian which is related to the macroscopic dielectric tensor in a very simple manner. The form of this effective Hamiltonian follows from symmetry considerations. From the measurements of the magneto‐optical effects, one determines the constants of the effective Hamiltonian and from these one can predict the cross section for Raman scattering of light by spin excitations.

ISSN:0021-8979    

DOI:10.1063/1.1709678

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Scattering of light by magnons has recently been predicted by calculations, and subsequently verified by experiments. In this paper, theoretical aspects of the problem are reviewed briefly. The spin‐Raman effect is treated along the same line as ordinary Raman scattering by phonons. The order of magnitude of one‐magnon Raman scattering is estimated from the rotatory power of the magnetic ions. The effect is smaller in antiferromagnets because of opposite spins in different sublattices. In ferrites and antiferromagnets, two‐magnon Raman scattering can occur through exchange‐type interaction. Raman scattering by magnetoelastic modes should also be observable. The possibility of constructing a tunable light oscillator is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1709679

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The thermal conductivity of single‐crystal UO2has been measured from liquid‐helium temperature up to room temperature. The sample temperature was determined, with a helium gas bulb thermometer, and the temperature gradient was measured with Au&sngbnd;Co vs Manganin differential thermo‐couples. In the vicinity of the Ne´el temperature,TN=30.8°K, the conductivity is depressed by two orders of magnitude, from that expected for a similar diamagnetic crystal. The experimental results demonstrate that a strong phonon‐magnon coupling exists in this crystal. The far‐infrared transmission of the same UO2crystal has been measured from a frequency of 5–115 cm−1at 3°K. A grating monochromator and a Strong‐type lamellar interferometer have been used for these measurements. A sharp absorption line has been found at 17.63±0.1 cm−1. Broader absorption lines have been observed at 19.2, 23, 79, and 100 cm−1. Transmission measurements in which a 50‐kG magnetic field is applied to the sample or the sample temperature is varied indicate that impurity‐induced absorptions occur at 19.2 and 23 cm−1, and the three remaining lines can be identified with the antiferromagnetic state of UO2.

ISSN:0021-8979    

DOI:10.1063/1.1709680

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The transmission of light through single crystals of EuO and EuS has been measured as a function of magnetic field, temperature, and wavelength. Below the Curie temperature, the intensity of light reaching the photodetector abruptly diminishes to nearly zero as the applied field is decreased below a critical fieldHcrit. This effect is caused by diffraction of light by magnetic domains. Photographs of the spatial distribution of transmitted light forH<Hcritshow that the light is rather uniformly distributed over large angles. This diffraction effect is largest near the optical band edge and diminishes at longer wavelengths. By measuring the temperature dependence ofHcritone may determine the ferromagnetic Curie temperature in a novel manner. For EuO we findTC=69.5°K, which agrees well with a Curie temperature determination on the same sample by a more conventional magnetization method.

ISSN:0021-8979    

DOI:10.1063/1.1709681

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Far‐infrared spectroscopy has been used extensively for the study of antiferromagnetic resonance, that is, single‐magnon excitations at the Brillouin zone center. The recent discovery of two‐magnon excitations in antiferromagnets by Halley and Silvera now permits precise measurements of magnon energies at selected points on the Brillouin‐zone boundary. The discovery and theoretical interpretation of the two‐magnon effect is described in this review paper. Experimental results for the antiferromagnets MnF2, FeF2, and CoF2and for the canted‐spin weak ferromagnets NiF2and MnCO3are also presented. The experimental data are discussed in relation to the current theoretical understanding of the two‐magnon effect.

ISSN:0021-8979    

DOI:10.1063/1.1709683

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A review of the well‐known magnetometer techniques for measuring magnetic properties is presented. Special attention is given to the peculiarities of each method which render it particularly attractive, or otherwise, for particular measurements. In addition, an attempt is made to estimate the investment in time and money required to implement the various techniques. Neutron diffraction methods and differential thermal analysis can also be used in the investigation of any magnetic material. Hence, they are included in this survey.

ISSN:0021-8979    

DOI:10.1063/1.1709684

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Various magnetic measurement techniques, not generally applicable to all magnetic systems, are reviewed. Specific examples of direct measurement techniques considered include difference or differential magnetization measurements with static or pulsed fields and ac (periodic) variations of magnetizationMor temperatureT(∂M/∂T, ∂T/∂H, ∂M/∂H). Special emphasis is given to ac techniques, because commercial ac electronic processing equipment now permits a wide variety of sophisticated investigations to be readily accomplished. A number of indirect techniques are briefly discussed, such as the numerous magnetic resonances which permit microscopic local field evaluations. Limitations of these indirect techniques and some of the assumptions generally made when applying them to deduce magnetic properties are emphasized. A short review of the production of high magnetic fields in superconducting, high‐power water‐cooled, and pulsed‐field solenoids is given, and production of very low fields is also briefly discussed. The last section considers measurement of magnetic fields, mainly high fields in low‐temperature environments, and very low fields.

ISSN:0021-8979    

DOI:10.1063/1.1709685

出版商:AIP    

年代:1967

数据来源: AIP