摘要:

We have studied the iron‐rich, rare‐earth‐iron intermetallic compounds R2Fe17(R = Pr, Gd, Tm, Lu), using the Mo¨ssbauer effect in57Fe. The measured average hyperfine fieldH(T/Tc) acting on the57Fe nuclei is a unique, monotonically decreasing function ofT/Tc, with no observed irregularity at temperatures corresponding to a suspected ferromagnetic‐antiferromagnetic phase transition in these compounds. The onset of paramagnetism occurs at temperatures close to theuppertransition points measured by Strnatet al., namely atTc= 282°, 472°, 271°, and 263°K for Pr2Fe17, Gd2Fe17, Tm2Fe17, and Lu2Fe17, respectively. Low‐temperature (≃90°K) spectra indicate the presence of at least four magnetically nonequivalent Fe sublattices, while forT>Tcbroadened 2‐line absorption spectra typical of57Fe at noncubic sites in paramagnetic material are observed.

ISSN:0021-8979    

DOI:10.1063/1.1659014

出版商:AIP    

年代:1970

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1659016

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

By the perturbation calculation within the Hartree‐Fock approximation, the free energy of electrons in metals is expanded as a power series of deviations of electron and spin densities from these in the ferromagnetic state up to the fourth powers. From the expansion, the wavevector‐dependent dielectric constant and spin susceptibilities are calculated. It is shown that in ferromagnetic itinerant electrons the external electric (magnetic) field induces not only an electron (spin) density but also a spin (electron) density. The discontinuity of the longitudinal spin susceptibility at zero wavevector in the case of a &dgr;‐function type interaction has been explained by the nature of interaction. Coefficients in the expansion are calculated at 0°K in the cases of sinusoidal distributions of electron and spin densities and of a helical distribution of spin density in a paramagnetic gas, where the effective mass approximation and the Hubbard approximation for the exchange terms are used. It is found that the coefficients of the fourth powers of these density waves diverge at a wavenumber 2kf, wherekfis the Fermi momentum divided by ℏ.

ISSN:0021-8979    

DOI:10.1063/1.1659017

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

We have calculated the exchange enhanced susceptibility function &khgr;(Q) for paramagnetic chromium attempting to include band structure effects in a realistic manner. First, the unenhanced diagonal element &khgr;0(Q, Q) of the susceptibility was calculated from an APW band calculation using the appropriate matrix elements and a Spline‐fit interpolation scheme to produce an effective mesh of 128 000 points in the zone. The result exhibited a peak corresponding to the wave vector of the spin‐density wave in chromium but differed quantitatively from previous calculations which ignored the matrix elements. Next, within the spirit of the RPA, the exchange enhanced susceptibility was obtained by approximately solving the coupled selfconsistent equations between the different Fourier components of the response to an applied field instead of simply dividing by the usual scalar denominator. This resulted in susceptibility functions which look similar to those obtained from a localized Heisenberg‐type Hamiltonian.

ISSN:0021-8979    

DOI:10.1063/1.1659018

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Low‐temperature measurements have been made of the saturated local momentpsatand the ordering temperatureTcof very dilute Fe in various Pd alloys. The alloy systems include Pd1−xAx, where A is Rh, Ag, Pt, and Ni and Pd1−2xRhxAgx(pseudo Pd). Bothpsatand the high‐field matrix susceptibility, &khgr;HF, were measured from 1.2° to 4.2°K and with fields to 60 kG. The alloys were fabricated with very dilute (∼1000 ppm) Fe in order to minimize impurity interactions and band splitting effects. The data indicate that the magnitude ofpsatis not simply proportional to &khgr;HF. These results are compared to previous higher temperature measurements of Pd alloys (with 1% Fe). The effects of impurity scattering onpsatandTcare discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659019

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The electrical resistivity of Pt&sngbnd;Ni alloys containing approximately 30, 35, 37, 40, 45, and 50 at.% Ni has been measured between 1.4° and 4.2°K. A clear resistance minimum is found for the two ferromagnetic samples, 45 and 50 at.% Ni, at 3.6° and 2.7°K, respectively. Although no minimum was found for the paramagnetic alloys, there was evidence of a turnup at low temperatures. All of the data could be fitted by the equation &rgr; = &rgr;0+AT2−BInT. Both coefficients,AandB, increase rapidly as the critical concentration for ferromagnetism is approached from both the paramagnetic and ferromagnetic sides. The application of a 20‐kG field to the 50 at.% Ni sample produced no detectable change in the temperature dependence of the resistivity. Ordering of this sample (by annealing at 600°C) yielded a paramagnetic state for which the coefficientAincreased by a factor of three and the InTterm was no longer observed. Although theT2term originates from electron‐electron scattering, the origin of the InTterm is not clear at the present.

ISSN:0021-8979    

DOI:10.1063/1.1659020

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The results of calculations of the magnetization and elastic neutron scattering in local moment‐ferromagnetic alloys are discussed and compared critically to other treatments in the literature.

ISSN:0021-8979    

DOI:10.1063/1.1659022

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The spatial dependence of the spin and charge response of a ferromagnetic metal is discussed by introducing theq‐dependent spin and charge susceptibility to a magnetic field &khgr;mm(q) and &khgr;em(q), and the spin and charge susceptibility to a charge potential &khgr;me(q) and &khgr;ee(q). The nondiagonal susceptibilities &khgr;meand &khgr;emare shown to be very important in ferromagnetic metals, since the effect of an impurity can be represented by the addition of both a chargeZeand spinS. Some of the essential features of neutron scattering experiments about impurities in ferromagnetic metals can be understood by properly including both the diagonal and nondiagonal susceptibilities.

ISSN:0021-8979    

DOI:10.1063/1.1659023

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Similar to Cu(Fe) or Au(V), the Al(Mn) system exhibits at low temperatures aT2negative dependence of its impurity resistivity. We present NMR data, taken on both27Al and55Mn. At helium temperatures, the55Mn resonance has a big negative Knight shiftK= −2.05%. Its spin‐lattice relaxation rate is frequency independent, and verifies a Korringa relationship. In high field, the27Al line is split into a main line and two satellites. The first one with &Dgr;K1/&Dgr;KAl= −1.09 is attributed to first nearest neighbors of Mn. The temperature dependence of the Knight shift of the first Al nearest neighbors is much bigger than expected, and can be described by a (T+&thgr;)−1law, with &thgr; = 2000±300°K. The fact that low‐temperature local susceptibilities are in good agreement with Hartree‐Fock theory and that the relaxation rate is frequency independent indicate that the localized spin‐fluctuation theory is appropriate to describe that system.

ISSN:0021-8979    

DOI:10.1063/1.1659024

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Amplified echoes can be described as a manifestation of nonlinear spin‐wave interaction in an inhomogeneous magnetic field. In a typical experiment a very small pulse is incident on a ferrimagnetic sample att=‐&tgr; and a large pulse is incident att=0. An echo is thereupon emitted att=&tgr; with an amplitude greatly exceeding that of pulse 1. The disturbances associated with the two incident pulses and with the echo can be represented by ``quasi‐stationary'' spin waves whose wave vectors vary with time on account of the field inhomgeneity. The wave vectors of the three waves are matched throughout and nonlinear coupling under proper conditions gives rise to unstable solutions in which the pair of spin waves associated with the pulse 1 and the echo grow exponentially at the expense of the spin wave generated by the large second pulse. Att=&tgr; the echo spin wave evolves into a uniform precession and at that time radiates a highly amplified echo. The process is generically related to the Suhl instability in a uniform ferrimagnet in which pairs of opposite spin waves grow exponentially at the expense of the uniform precession mode. A simple mathematical model is introduced to illustrate this behavior.

ISSN:0021-8979    

DOI:10.1063/1.1659025

出版商:AIP    

年代:1970

数据来源: AIP