摘要:

The present work reports the theoretical considerations of the effects of nontrigonal crystal field on the electronic structure of ferrous ions induced by tetravalent dopants in YIG. It is found that a spin Hamiltonian can well acount for the spectroscopic properties of the ground orbital singlet of the ferrous ion in YIG. A numerical method is worked out to calculate the parameters involved in the theory, namely, the three second‐order and the five fourth‐order zero‐field parameters, and the four components of the Zeeman g‐tensor. A wide range of the microscopic parameters is considered and some representative results are given. The properties of the nearby (I) and far (II) ferrous centers can now be well explained. The centers II are shown to be more anisotropic than the centers I. The dominant second‐order axial parameter is found to be positive and of the value of several inverse cm.

ISSN:0021-8979    

DOI:10.1063/1.326809

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The mechanisms of the ME effect of Cr2O3were experimentally determined at 4.2 K. For this purpose, ME susceptibility was measured statically by SQUID from 1.6 to 270 K and the electric shift of AFMR was observed at 4.2 K by an ac modulation method. The former experiment gave &agr;∥(4.2 K) =−0.8, &agr;∥(255 K) =15.3 and &agr;⊥(4.2 K) =−4.7 in 10−4cgs unit. The latter gave a frequency shift of −1.02×10−6cm−1at E=1 cgs in the case of both E&drarr; and H&drarr; parallel to the c axis. From these experiments, &dgr;g=−1.05×10−8and &dgr;D=−3.3×10−6cm−1were deduced for E=1 cgs along the c axis. This value is not only too small but of the wrong sign to explain the sign and the magnitude of &agr;∥at higher temperatures. &agr;⊥at 4.2 K seems too large to be interpreted by the tilting of the easy axis of spins and the role of other mechanisms such as the appearance of a Dzyaloshinski interaction is suggested.

ISSN:0021-8979    

DOI:10.1063/1.326810

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

In magnetically ordered crystals, which are deprived of anti‐inversion as a symmetry operation, a new magnetooptical effect is permitted. It consists in appearance of a birefringence of the linear polarized light directly proportional to the magnetic field strength as opposed to the quadratic Cotton‐Mouton and Voight effects. The appearing birefringence is connected with inducing the nonequivalency of magnetic sublattices by a magnetic field. The sign of the linear magnetooptical effect depends on the directions of the sublattice magnetic moments and the magnetic field strength. It is determined by sign of the antiferromagnetic vector projection on some axis only if the magnetic field direction is constant. This circumstance gives a possiblity of visualizing the regions of the crystals having oppositely oriented antiferromagnetic vectors. The visual observation of the 180‐degree antiferromagnetic domains in the two‐sublattice antiferromagnetic cobalt fluorite by means the new linear magnetooptical effect is reported.

ISSN:0021-8979    

DOI:10.1063/1.326811

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A strong external magnetic field, Hc=176 kOe, applied along the ordering axis of antiferromagnetic NiWO4produces spin flopping. This orientational transition results in sharp changes both in longitudinal and transverse components of the magnetization vector. It is found that for certain external magnetic field orientations, spin flopping in NiWO4is a first order phase transition. The measurement results for magnetic properties suggest that an intermediate state appears in this field region, where the sample laminates into magnetic domains. The domain layer directions make an angle with the vector of the inducing magnetic field, which can be varied by minor changes in the external field direction.

ISSN:0021-8979    

DOI:10.1063/1.326812

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The Panel, under the chairmanship of S. P. Keller, was created by the Solid State Sciences Committee, National Research Council, at the request of and with the support of the National Science Foundation. The Panel consisted of four subpanels: Scientific Opportunities, Raymond L. Orbach, chairman; Applications, John K. Hulm, chairman; Magnet Design and Materials, Bruce Montgomery, chairman; and High Magnetic Field Facilities and Users, Bruce D. McCombe, chairman. The major recommendations were I. A design program should be started to determine methods for producing steady state, highly homogeneous, magnetic fields up to 75 T. It is recommended that fields of 45 T and 60 T be the intermediate goals along the way to 75 T. II. The design and construction of quasistatic pulse magnets with fields approaching 100 T should be undertaken. III. The design and construction of short pulsed magnets affording fields greater than 1000 T should be undertaken. In addition to these primary recommendations, there were others dealing with i. The support of research in superconducting materials and processing techniques. ii. The funding of facilities for supporting equipment (e.g., optical spectrometers). iii. The support of research exploiting the high magnetic fields recommended above. iv. Funding for adaptation of energy sources developed for other applications to high magnetic field installations. Report published by National Academy of Sciences, Washington, D.C. (1979)

ISSN:0021-8979    

DOI:10.1063/1.326813

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A new method has been developed at Osaka University for producing a mega‐gauss field without destruction of the coil. As one of the applications of this system, submillimeter ESR experiments have been done at low temperatures by using HCN (&lgr;=337&mgr;m) and H2O (&lgr;=119&mgr;m) lasers in a field up to 0.5 MOe. We report some novel high field effects observed in these experiments. The g‐shift due to the SH3term is expected to be appreciable in such a high magnetic field. This effect was found in a study of Co‐Tutton salt at 77 K. The experimental result showed 2% smaller g value at 119 &mgr;m than at 337 &mgr;m. This was explained quantitatively by an extensive calculation based on the Abragam‐Pryce theory. So‐called exchange splitting was observed in (NH4)  2CuCl4⋅2H2O, Cu(NH3)  4SO4⋅H2O (CTS) and CuCl2⋅2H2O. At 4.2 K the two observed lines were of quite different intensities and the weaker one showed a remarkable shift. These phenomena can be explained successfully by molecular field theory, and it is shown from the direction of the shift that the exchange interaction between inequivalent spins is antiferromagnetic for CTS and ferromagnetic for the others.

ISSN:0021-8979    

DOI:10.1063/1.326814

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A pulsed, high current machine has recently been developed for producing pulsed magnetic fields in the 70 Tesla range, with long operational life of the load inductor. The current source, which drives a single‐turn solenoid, is a high voltage, low inductance capacitor bank. Connections from the capacitor bank to the inductor are by way of low inductance multichannel rail spark gap switches and low inductance buswork. Peak magnetic fields of 72 Tesla have been measured in the bore of the single‐turn inductor. These measurements have been made using the magneto‐optical, Faraday, effect. The pulsed magnetic machine has recently been used to develop enclosure welds on tubing which is being evaluated as possible cladding material in nuclear reactors.

ISSN:0021-8979    

DOI:10.1063/1.326815

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

In the generation of intense magnetic fields using copper wire‐wound solenoids an upper field limit is often imposed by Lorentz forces in the conductor. The use of materials such as 2% Be‐Cu alloy increases the maximum stress permitted fields, but their high resistivity leads to an unfavourable energy limitation. The use of copper‐clad steel however enables the roles of conductor and strengthener to be separated and by varying the copper/steel ratio to be almost independently controlled. Using a given energy source the energy limitation is determined taking Joule heating into account by an iterative computer technique. The stress limitation is determined1taking the Youngs moduli of copper, steel and insulation into account. Calculations have been made using a range of energy sources and pulse lengths of 1 ms and 10 ms. By varying the copper/steel ratio it is possible to design an optimum coil for which the energy and stress limitations coincide. It is found that in most cases, fields higher than those possible with pure copper wire are obtainable, with increases in maximum field of up to 30%. Practical examples of such coils will be presented and the problems associated with winding copper steel composite coils will be discussed. In addition it will be shown that the steel component has a well defined effect on the field profile of the solenoid at low magnetic fields.

ISSN:0021-8979    

DOI:10.1063/1.326817

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Ancient ceramics may be characterised by their magnetic hysteresis loops. Spontaneous and remanent magnetization and coercivity can be used to distinguish groups of ceramics fired in different conditions. Information about the firing conditions is obtained by comparing the magnetic parameters of the sherds with those of laboratory‐fired paeleosols. The method is illustrated with reference to contemporary red, buff and grey ware (c 3000 BC) from the period II of Tureng Tepe and Tepe Hissar, two related sites in northeastern Iran. In some cases the firing temperature can be estimated to within 50 C, and groups of sherds fired in oxidizing, reducing or mixed atmospheres are identified. An explanation of the firing temperature dependence of the hysteresis loop parameters in the range 400–1200 C is based on the proportions of iron diluted in silicates and in superparamagnetic or stable iron oxide particles, derived from magnetic and Mo¨ssbauer data. An assessment is given of the potential of simple magnetic measurements in archaeometry.

ISSN:0021-8979    

DOI:10.1063/1.326818

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The magnetic properties of material artifacts depend on their bulk compositions, the phase assemblages, the crystal‐ and micro‐structures of the phases and their thermal histories. The magnetic properties of an object formed from chemically pure elements and compounds are independent of the origins of the source materials. However, most archaeological artifacts are not made from pure elements and compounds and contain sufficient quantities of impurity atoms and ions to cause variations in magnetic properties that are traceable to variations in the impurity concentration of the source materials. Nevertheless, the relationship between the magnetic properties and provenance of an artifact reflects more than chemical composition. The utilization of data consisting of single numbers or low dimensional correlations among such numbers, i.e., as in chemical analysis, has severely hampered the progress of ’’sourcing’’ studies. The experimental techniques discussed overcome this limitation by providing data that are graphical and that include a large number of parameters as well as correlations among these parameters in a single measurement. These techniques include those of Mo¨ssbauer spectroscopy and temperature dependent magnetization studies. The data obtained in these two instances are graphical and exhibit simultaneously effects due to bulk composition, the phases present in a multiphase assemblage, crystal structure, magnetic structure, composition within a given phase and the microstructures of the phases. In many instances it is not necessary to perform extensive data analysis to establish a correlation between a possible source material and an archaeological artifact. The successful application of Mo¨ssbauer spectroscopy to provenance studies of iron ore artifacts from Mesoamerica will be discussed. It appears that this technique can also be extended to glass and a limited number of alloy artifacts. Thermomagnetic measurements have yet to be employed in provenance studies but the potential for application is clear.

ISSN:0021-8979    

DOI:10.1063/1.326820

出版商:AIP    

年代:1979

数据来源: AIP