摘要:

We have measured the temperature dependence of the thermoelectric powerS(T)for eight samples of Au(Fe) alloys with concentrationscup to 22 at.% Fe in the temperature range 4°–300°K.S(T)for all samples is always negative and shows a maximum in |S| between 80° and 110°K. For samples withc>12% Fe there are well‐defined transitions in the behavior ofS(T)at temperatures agreeing with the ordering temperatures as determined by other measurements, whereas no distinct transitions are observed forc<12%. These two concentration groups also differ in the concentration dependence of the magnitude ofS(T)and in the temperature dependence of the position of the maximum of |S|. At low temperatures we find thatS(T)follows a behavior:S=AT3/2+BT5/2which suggests a magnon drag contribution toS(T).

ISSN:0021-8979    

DOI:10.1063/1.1658971

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Hall effect and transverse magnetoresistance have been measured in fields up to 7 T (70 kG) in polycrystals. The Hall data for two samples of pure iron (&rgr;300/&rgr;4.2= 1991 and 507 in small longitudinal fields) and for alloys with 0.25%, 0.50%, 0.92% Co fall roughly on the same Kohler curve as the iron data of Dheer if the resistivity in small longitudinal fields is used to construct the Kohler diagram. This curve is curved downwards at &ohgr;c&tgr; ≈ 1, indicating the presence of more than two bands. For pure iron, extrapolation of the tangent of Hall angle to the high‐field limit gives tan&phgr;H= (−2.2±0.5) × 10−2; a finite asymptotic value is predicted for a compensated magnetic metal, on the basis of asymmetric scattering. Extrapolation to the low‐field limit for Fe&sngbnd;Co gives tan&phgr;H= (+1.4±0.2) × 10−2; a finite value is also predicted from asymmetric scattering. Contribution to Hall voltage from the nonclassical Kohn‐Luttinger mechanism reaches 15% for the 0.92% Co sample, and must be subtracted from data.

ISSN:0021-8979    

DOI:10.1063/1.1658972

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Measurement of the temperature dependence of resistance and magnetoresistance in single crystals of iron have been made in the temperature range 0.3° to 4.2°K. Samples with residual resistivity ratios of 1000–4000 were used. In the temperature range 1° to 4.2°K measurements have been made in applied magnetic fields up to 50 kOe. The data have been fitted by computer to expressions for the resistance and in all cases bothTandT2terms are present. In the range 1° to 4.2°K a strong linear term is present as was previously reported.1Below 1°K theT2term appears to become more dominant and at temperatures less than 0.8°K the data appear to fit an exponential down to the lowest points measured. The coefficients are strongly affected by applied magnetic fields up to 1200 Oe. However, for 50 kOe fields the changes are much smaller than might be expected. The data will be discussed in terms of electron‐magnon scattering, electron‐electron scattering, and other possible contributions to the temperature dependence of resistance in the helium range of temperature.

ISSN:0021-8979    

DOI:10.1063/1.1658973

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Electrical resistivity &rgr; has been studied as a function of temperatureTof chromium alloys containing 0.9, 2.1, 3.0, and 4.8 at.% Ru and 0.3, 0.6, 1.1, and 2.0 at.% Os. The onset of antiferromagnetism causes large anomalies in the &rgr; vsTcurve. The Ne´el temperaturesTNof both alloy systems increase rapidly with increasing solute concentrations up to 2 at.%, remain approximately constant, and then decrease with larger solute contents. The initial increase inTNwith increasing solute concentration can be understood by Fedders and Martin's theory assuming that additions of Ru and Os to Cr cause an increase in the electron jack and a decrease in the hole octahedron which enlarge the interaction area of the two Fermi surfaces. The incommensurable antiferromagnetic structure in both alloy systems exists up to about 0.5 at.%. For higher concentrations the antiferromagnetic phase, bordering the paramagnetic region, is commensurable with the lattice. The large increases in the electrical resistivity of the commensurable antiferromagnetic alloys is interpreted as resulting from the superlattice boundaries. For incommensurable phase alloys the resistivity anomaly is due to mutual annihilation of hole and electron Fermi structures.

ISSN:0021-8979    

DOI:10.1063/1.1658974

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

We discuss the transverse magnetoresistance of nickel at low temperature and its dependence on residual impurity. It appears from our results on some nickel dilute alloys that the difference between the relaxation times of spin ↑ and spin ↓ conduction electrons is a dominant mechanism for the magnetoresistance.

ISSN:0021-8979    

DOI:10.1063/1.1658975

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Magnetic and transport measurements in ferromagnetic EuB6show (a) evidence for a Fisher‐Langer‐type resistance anomaly nearTc, (b) that EuB6may not be a simple ferromagnet, and (c) that the magnetic coupling might be influenced by a temperature‐dependent conduction electron concentration.

ISSN:0021-8979    

DOI:10.1063/1.1658976

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The long‐wavelength spin dynamics of the ferrimagnet magnetite (Fe3O4) have been investigated at and below the critical temperatureTc. The magnetic fluctuations were observed in zero magnetic field near the (111) Bragg peak by triple axis neutron spectrometry. Well belowTcthe dynamics can be described in terms of spin‐wave excitations whose energy isDq2. Over the temperature range 0.6>1 ‐T/Tc>0.01,Dis found to vary as (Tc‐T) to the power 0.265±0.03. Within about 1% ofTcthe spin‐wave lines broaden rapidly and become over‐critically damped. AtT=Tcthere are no signs of spin‐wave excitations and the energy width of the neutron scattering function varies asqto the power 1.65±0.20 over the range 0.05≤q≤0.16 Å−1.

ISSN:0021-8979    

DOI:10.1063/1.1658977

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The thermal conductivity of the antiferromagnet MnCl2·4H2O has been measured from 3° to 0.25°K with particular attention to the region of the Ne´el point (TN= 1.62°K). The effects of magnetic scattering are separated from the thermal resistance arising from nonmagnetic processes by comparing the thermal conductivity measured in a magnetic field of 40 kOe with that measured in zero applied field. It is found that in the paramagnetic phase there is no critically enhanced phonon scattering associated with the magnetic ordering transition. In the ordered phase the magnetic contribution to the scattering has a maximum near 0.75°K and diminishes as the transition is approached. Detailed comparison with theoretical predictions is made, and the relationship of this work to recent measurements of thermal expansion and specific heat is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1658978

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The critical spin fluctuations in MnF2have been studied near the Ne´el temperature using a triple axis spectrometer with high resolution. The experimental data were analysed in terms of the static susceptibility and the spectral shape function. The results can be summarized as follows: The longitudinal component &khgr;∥(q) of the static susceptibility behaves as expected for a Heisenberg magnet, &khgr;∥(q= 0) ∝ [(T ‐ TN) /TN]−1.35±0.01and &kgr;1∥= 0.27[(T ‐ TN) /TN]0.68±0.03where &kgr;1∥is the longitudinal inverse correlation length. The corresponding transverse component&khgr;⊥(q)is suppressed by the anisotropy. In terms of the suppressed Ne´el temperatureT⊥introduced by Moriya (1962) the temperature dependences were&khgr;⊥(q=0)∝[(T−T⊥)/T⊥]−0.85±0.03and&kgr;1⊥=0.21[(T−T⊥)/T⊥]0.45±0.01. The characteristic widths of the spectral shape functions varied as &Ggr;∥(q= 0) = 1.5[(T ‐ TN) /TN]0.62±0.02and&Ggr;⊥(q=0)=1.4[(T−T⊥)/T⊥]0.53±0.05indicating thermodynamic showing down for the longitudinal component. The exponent 0.62±0.02 of &Ggr;∥(q= 0) is in bad agreement with the existing theories but is consistent with the similar exponent found in RbMnF3by Nathans, Menzinger, and Pickart (1968). Theq‐variation of the transverse width&Ggr;⊥(q)was consistent with theq3/2‐law predicted by dynamic scaling.

ISSN:0021-8979    

DOI:10.1063/1.1658980

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The scattering of slow neutrons by the critical fluctuations of thezcomponent of the magnetic moments in the antiferromagnet CoF2has been measured at fourteen temperatures both above and below the Ne´el temperatureTN. The most unexpected feature of the results is that in contrast to similar measurements on MnF2and RbMnF3no inelasticity of the scattering was observed at any temperature. This implies long‐lived magnetic fluctuations (>1.6 × 10−11sec) at temperatures up to 2.1TN, and is probably associated with the occurrence of the fairly well‐defined spin waves observed earlier. The results for the intensity of the scattering as a function of wave vector transfer are compared with recent theories of the critical effects in the Ising model.

ISSN:0021-8979    

DOI:10.1063/1.1658982

出版商:AIP    

年代:1970

数据来源: AIP