ISSN:0021-8979    

DOI:10.1063/1.1714254

出版商:AIP    

年代:1965

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1714255

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

In oxidic lattices the Co3+(3d6) ion has been found both in the diamagnetic low‐spin state and in the paramagnetic high‐spin state. The factors influencing the equilibrium between high‐ and low‐spin Co3+ions are discussed.New compounds are presented in which the change of the equilibrium distribution among these two states is measurable because the energy difference between the two states is small. It is then possible to change the equilibrium by varying the temperature. The temperature dependence of the magnetic susceptibility of such a compound is anomalous as has been derived by Ballhausen and Liehr.

ISSN:0021-8979    

DOI:10.1063/1.1714256

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A review is given of the problems in this field, and of the possibilities opened up by the fact that neutron scattering gives access to the time‐dependent spin‐correlation function in magnets over virtually the whole range ofq, t, andT. New experimental results are given in connection with magnon energy linewidth and renormalization, and some data are presented for the spin‐wave stiffness of bcc 3dtransition‐metal alloys as a function of electron concentration, showing effects explained by the electronic density‐of‐states curve. It is pointed out that the ground‐state fluctuations of magnets give rise to effects in the formulas for neutron scattering.

ISSN:0021-8979    

DOI:10.1063/1.1714257

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The advent of high‐field superconducting magnets has made magnetic fields above 30 kG available to the entire scientific community. Small diameter coils to 60 kG cost considerably less than conventional 12‐in. iron magnet systems. Fields to 80 kG, and in a few recent instances to 100 kG, even in multicentimeter bores, are now economically within the reach of most research budgets. The current and future status of superconducting magnets, their economic advantages and associated problems are presented. Other methods of generating fields, such as water‐cooled continuous magnets, millisecond pulse magnets, and long‐pulse cryogenic magnets, will find their principal use in reaching even higher fields, supplementing superconducting magnets, or in circumventing problems which preclude the use of superconductors. Pulse magnets are presented as a relatively simple and inexpensive method of producing millisecond fields up to 500 kG and long pulses to 250 kG. Relationships between energy, time, and volume are given for pulse magnets. The current and future status, and the problems associated with conventional continuous field magnets in the 100 to 250 kG range are given and the availability of such magnets at the National Magnet Laboratory discussed. New critical current—critical field data for niobium—tin materials measured in continuous fields up to 180 kG is presented.

ISSN:0021-8979    

DOI:10.1063/1.1714258

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Studies are described of the ferrimagnetic garnet system Eu3Fe5—xGaxO12. It is shown that a compensation point of the net angular momentum occurs atx≅1.2, at which the resonance linewidth remains narrow. In all previously observed ferrimagnetic systems with angular momentum compensation points, e.g. GdIG, strong line broadening occurs. The reasons for this are discussed together with the relaxation processes involved. Application of the resulting largegfactors to millimeter wave harmonic generation is considered.

ISSN:0021-8979    

DOI:10.1063/1.1714259

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

In metals and alloys containing localized magnetic moments, an important contribution to the electrical resistivity can be associated with disorder of the atomic spin system. This contribution is ascribed to a scalar interaction between the spins of the conduction electrons and the atomic spins. Assuming a simple form for this interaction, the experimental and theoretical situation concerning the spin‐disorder resistivity is reviewed for pure metals, dilute alloys, and concentrated binary alloys.

ISSN:0021-8979    

DOI:10.1063/1.1714260

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

It has been observed that the Mo¨ssbauer spectra of many ferromagnetic alloys can be analyzed to give the effect on the internal field at an57Fe nucleus of a solute atom in any of the first six neighbor shells surrounding an Fe atom. The success of such an analysis indicates that the effects of many elements (e.g., Al, Si, Mn, V, Cr) are quite localized and, in particular, the results of the Al and Si alloys indicate that these atoms can be interpreted as acting like holes in the Fe lattice. From considerations of the various contributions to the hyperfine field in Fe, it appears that for the FeAl and FeSi alloy systems the observed changes can be attributed to changes in the spin polarization of thesconduction electrons as a function of distance from an Fe atom. The main features of the observed variation are: (a) an oscillating polarization whose amplitude of oscillation is much greater than that corresponding to a Ruderman‐Kittel‐Kasuya‐Yosida type calculation and whose sign is such as to show that the indirect exchange interactions in Fe via the 4sconduction band are strongly antiferromagnetic; and (b) the period of the oscillation corresponds to a Fermi radius,kF∼0.95×108cm−1, which yields a 4sconduction electron/atom ratio of about 0.3. With the assumption of a reasonable magnetic form factor for Fe (that from neutron diffraction measurements), the observed polarization can be Fourier inverted to give the spin susceptibility of thesconduction electrons in Fe. The results of such an inversion yield a spin susceptibility function which has a large peak at the Fermi diameter.

ISSN:0021-8979    

DOI:10.1063/1.1714261

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The55Mn NMR has been observed in the paramagnetic state of the antiferromagnet MnO. The separation between the absorption derivative extrema of the55Mn NMR is55(&dgr;H)≃340 Oe, in satisfactory agreement with the predictions of exchange narrowing of hyperfine broadened nuclear magnetic resonances in paramagnetic media. The55Mn NMR frequency shift55a=(&dgr;v/v) is found to be temperature dependent, varying from about −11.75% to −9.3% in the range 130° to 350°K. From the observed linear dependence of55aon the magnetic susceptibility, the hyperfine coupling constant is determined to be55A=−(81.5±1.6)×10−4cm−1. Combining the17O NMR data of O'Reilly and Tsang with the55Mn NMR data yields a value for the17O transferred hyperfine coupling constant of17A=(2.46±0.04)×10−4cm−1.

ISSN:0021-8979    

DOI:10.1063/1.1714262

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

It was pointed out some time ago by Abragam and Pryce that there was an anomalous part of the hyperfine field (approximately −200 000 G per unit electron spin) that was essentially constant in the 3dions. This anomalous field arises from admixture of configurations with unpairedselectrons. Alternatively, it has been viewed as a spin polarization of the inner coreselectrons by the outer 3delectrons. Increased precision of measurement, aided by ENDOR in some cases, reveals some striking constancies with regard to this core polarization hyperfine field (cphf). First, it is found that the cphf within an isoelectronic sequence in the same type of ligand coordination is constant to within a few percent. It may change as much as 40% depending upon environment but in the same type of environment (same ligand number and ligand ion) it is constant, i.e., the cphf isindependent of the charge on the nucleus. The second interesting fact is that the cphf isindependent of ligand distance, i.e., it is the same within a few percent in MgO, CaO, and SrO. Aside from these two invariant features, there seems to be a monotonic increase across the 3dseries in the cphf field in accord with the prediction of Freeman and Watson. These systematics will be illustrated in detail and some very tentative explanations for this behavior offered.

ISSN:0021-8979    

DOI:10.1063/1.1714263

出版商:AIP    

年代:1965

数据来源: AIP