摘要:

Magneto‐transport measurements of noble metals containing rare‐earth impurities probe different aspects of the 4f‐conduction electron interaction. The anisotropy of the magnetoresistance is primarily due to the quadrupolar term, the extraordinary Hall effect (skew scattering) is at least partially due to the orbital exchange term (l⋅L) and the negative isotropic magnetoresistance is due to the spin exchange term (s⋅S). The advantage of magneto‐transport experiments over others, e.g., EPRg‐shift and linewidth, is that they single out different terms in the 4f‐conduction electron interaction. Estimates of the anisotropic terms based on conduction electrons in plane wave states give values too small to explain the experimental data. We have taken into account the admixture of 5dscreening electrons into the conduction band and obtain a 4f‐conduction electron interaction which has large anisotropic terms in addition to the conventional spin interaction. When we assume that the 5delectrons are int2gstates we find that our estimate of the anisotropy of the magnetoresistance and of the skew scattering effect are in fair agreement with the experimental data. However, our estimate of the negative isotropic magnetoresistance is too large.

ISSN:0021-8979    

DOI:10.1063/1.324719

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Anisotropy from the quadrupole scattering contribution to the electrical resistivity of magnetically ordered rare‐earth compounds is examined. Considering the conduction electrons in plane‐wave states, we find that the principal contributions to the anisotropic scattering come from thepanddpartial wave scattering. We take into account the crystal field splitting of the rare‐earth ions’ 4fnelectrons and therefore include the effects of inelastic scattering. We consider the case of zero magnetic field so that anisotropy only appears below the ordering temperature of the system. The theory is applied to dysprosium and holmium antimonide.

ISSN:0021-8979    

DOI:10.1063/1.324720

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

We review the behavior of the thermopower, magnetothermopower, and magnetoresistivity of dilute PtCo alloys, and present new results which extend the thermopower data to lower Co concentrations, the magnetothermopower to higher temperatures, and the magnetoresistivity data to higher Co concentrations. We report the first observation of a negative magnetoresistivity in PtCo.

ISSN:0021-8979    

DOI:10.1063/1.324721

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Ni‐Co alloy is worth notice as a material for fabricating a magnetoresistance element, because of the highest magnetoresistance anisotropy (&Dgr;&rgr;/&rgr;0) in the ferromagnetic alloys. We studied the magnetoresistance anisotropy and the crystal structure on the films of the Ni‐Co alloy system (40 Ni–60Co∼81Ni–19Co). In this study we found the following facts: (1) A new ordered phase exists in the films around at the composition 50Ni–50Co prepared at a substrate temperature above about 550 °K. (2) This ordered phase is accompanied with a newly proposed superstructure. (3) A close relation exists between the magnetoresistance anisotropy and the degree of order, and the films in the ordered state have a higher anisotropy ratio (&Dgr;&rgr;/&rgr;0) than the bulk value. This fact is important in the practical application, such as a magnetic field sensor.

ISSN:0021-8979    

DOI:10.1063/1.324722

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Magnetic field dependent correlation functions for antiferromagnets near the spin flop‐paramagnetic phase boundary have been calculated using an RPA technique. The exponents describing the field dependence of the magnetization, the staggered magnetization and the correlation length, which are obtained from these calculations, are compared to those obtained using renormalization groups results. Here, we use our recent results relating the symmetry forbidden one‐phonon Raman scattering in magnetic semiconductors to the two‐spin correlation function, to calculate the field dependence of the Raman integrated intensity in EuTe. Light scattering experiments are suggested where the exponents related to the spin flop‐paramagnetic phase boundary,Hc(T), and the field dependence of the staggered magnetization can be measured from the one phonon–one spin Raman spectrum in EuTe.

ISSN:0021-8979    

DOI:10.1063/1.324723

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Spin‐dependent (SD) phonon Raman scattering in ferromagnetic CdCr2X4is closely associated with the resonance effect. In order to clarify the correlation between the excitation energy dependence of the SD phenomenon and the electronic structure, detailed temperature dependences of absorption and Faraday rotation spectra were measured between 20 and 300 K for ’’red‐shifting (RS)’’ transitions in CdCr2S4∼1.9 eV) and CdCr2Se4(∼1.2 eV). We found that the RS absorption peaks consists of a pair of electronic transitions with the energy separation of about 0.07 eV at 20 K. It turned out that the SD scattering cross section for Raman active phonon modesT2gandA1gin CdCr2S4observed with red excitation light are caused by the resonance with the pair transitions. Magnetic circular polarization properties of Raman spectra for CdCr2S4were measured in the applied fields up to 45 kOe in the Faraday configuration. The polarization and field‐induced effects observed with Kr 647.1 nm excitation light support the idea of SD resonance scattering. SD effects for phonon modesT2gandA1gare also found with higher excitation energiesC1(2.4 eV; CdCr2S4, 2.0 eV;CdCr2Se4) andC2(2.3 eV;CdCr2Se4), respectively. The correlations between the SD phonon scattering and the electronic structures are discussed on the basis of proposed transition diagrams.

ISSN:0021-8979    

DOI:10.1063/1.324724

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A new technique for the coherent excitation of magnons is proposed which is based on the magnetic Raman nonlinearity. The excitation is obtained by mixing two laser beams with different frequencies (&ohgr;1,&ohgr;2) under phase‐match conditions [when (&ohgr;1−&ohgr;2) is equal to the frequency of one magnon mode and (k1−k2) is equal to the magnon wavevector]. The method allows selective excitation in frequency and wavevector and may by useful for magnon relaxation measurements. The proposed process is analyzed by quantum statistical methods. The number of excited magnons and the coherence properties of the generated states are investigated by using the representation of coherent magnon states. The results show that it is possible to excite a magnon population of the same order of magnitude as in nonlinear magnetic resonance experiments by using lasers with powers of hundreds of watts. The possibility of experimental observation is analyzed in detail for both ferromagnetic and antiferromagnetic materials.

ISSN:0021-8979    

DOI:10.1063/1.324725

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Raman scattering from high energy excitons has been measured in KNiF3, K2NiF4, NaNiF3and NiF2with the help of ultraviolet laser excitation. AtT=2 K, the spectra consist of sharp excitonic lines, accompanied by a broad vibronic band showing pronounced structure. Attention is focused on Raman transitions from the3A2gground state to the3T2g(∼6500 cm−1) and the3Ta1g(∼11 000 cm−1) excited states. The observed polarized spectra and their dependence upon an applied magnetic field are compared with previous absorption measurements on the same crystals and are discussed in terms of magnetic excitons.

ISSN:0021-8979    

DOI:10.1063/1.324726

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

It is shown from experiment that a rotaion &rgr; and a deformation &khgr; of the optical indicatrix appear during the transverse field‐induced phase transition in hematite. Strong dependence of &rgr; and &khgr; on the temperature, magnetic fieldHaand the angle &PSgr; corresponding to the direction ofHawith respect to theC2axis in the basal plane are observed. During the Morin transition, the evolution of the linear magnetic birefringence is very sensitive to the magnetic phase transition and this evolution is discussed from the dependences of the analytical expressions of &rgr; and &khgr; on the rotation of the antiferromagnetic vector L.

ISSN:0021-8979    

DOI:10.1063/1.324727

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The field dependence of the low temperature infrared fluorescence of Ni2+in MnF2up to 110 kG is reported and the changes occurring at the spin‐flop transition at 94 kG are analyzed. These are accounted for by an upward shift of the fluorescent state energy of 16.7 cm−1and a modification of the ground term splittings. Both effects are shown to arise from the flip of the sublattice magnetizations from the [001] to the [100] directions. From the measured shift of the excited state the exchange energy for the3T2term is estimated to be about 110 cm−1.

ISSN:0021-8979    

DOI:10.1063/1.324728

出版商:AIP    

年代:1978

数据来源: AIP