摘要:

The effective internal field (2HEHA)½as well as its temperature dependence has been found from antiferromagnetic resonance experiments for two different single crystals of MnTiO3, and from absorption edge data for a pure powder sample. The data are consistent with a uniaxial collinear two sublattice model as predicted from dc susceptibility and neutron diffraction measurements. The data for one crystal yielded results in good agreement with the powder material with agvalue of 2.1 and effective internal field of 52 kgauss at 4.2°K. All samples followed a Brillouin function for spin52fairly well but with different Ne´el temperatures higher than that previously reported for this material.

ISSN:0021-8979    

DOI:10.1063/1.1728703

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Antiferromagnetic and paramagnetic resonance absorption has been measured in CuF2·2H2O. At 1.4°K, the antiferromagnetic resonances in zero field occur at 95.84±0.05 kMc and 95.91±0.05 kMc. The easy direction of magnetization occurs at an angle of 3.5° with thecaxis. This orientation is in agreement with neutron diffraction and single‐crystal susceptibility measurements. Due to strong exchange narrowing, narrow paramagnetic resonance lines were observed. Thegvalues areg&xgr;=2.07,g&eegr;=2.08, andg&zgr;=2.42. The principal axes are nearly coinciding with the ligand directions. From thegvalues, the energy levels and wave functions of the Cu++ions are determined. A discussion of the anisotropy is given. The dipolar part is calculated numerically, and the anisotropic exchange of pseudodipolar type is determined, using the fact that &ohgr;1∼&ohgr;2and the known easy magnetization direction. From the total anisotropy determined in this way, and the perpendicular susceptibility measured by Williams, the antiferromagnetic resonance frequency is predicted to occur at 130 kMc. The agreement with experiment is not unreasonable in view of the reduction of this frequency by the zero‐point oscillations of the spin waves. A brief discussion of the superexchange interaction in this crystal is given.

ISSN:0021-8979    

DOI:10.1063/1.1728704

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The dc voltage which accompanies ferromagnetic resonance has been observed in thin films of magnetite. The dependence of this voltage on microwave power and static magnetic field is in qualitative agreement with theory, but larger by a factor of 3.

ISSN:0021-8979    

DOI:10.1063/1.1728705

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The ``local field'' is the electric or magnetic field of external sources and of all molecules or particles except the one under examination, at the position of that one. The concept is useful in the molecular theory of dielectrics, where the basic relations are linear. It has also been applied, however, to magnetically interacting single‐domain particles in a ferromagnetic powder; here the relations not only are nonlinear but involve discontinuous irreversible jumps, for which instability conditions are decisive. The local‐field concept is then unreliable. In a two‐particle system, for example, the local‐field method examines the stability of one moment with respect to rotation in a fixed field due to the other moment and to external sources; this procedure imposes a constraint, for in the actual system the two moments may rotate simulatneously and independently. The incorrectness of the local‐field method is demonstrated here by calculations for two‐and three‐particle chains of spheres and for two‐ and three‐part composite cylinders. The concept of an interaction field that merely displaces the hysteresis loops of the particles without changing their widths, as in a common interpretation of the Preisach model, is thus erroneous.

ISSN:0021-8979    

DOI:10.1063/1.1728706

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A brief review of the progress of the ``Alnico Art'' is given, tracing early attempts at increasing energy yield by changes in composition to present day techniques of promoting polycrystalline growth parallel to the magnetic axis. Energy product values have steadily risen to the present commercially available level of 7.5 (MGO). Since research has apparently reached a temporary impasse in further improvement in polycrystalline Alnico magnets, except by an uneconomic fabrication from a much larger initial casting or expensive foundry mold techniques an, attempt to take advantage of the 12.0 mega gauss‐oe energy product available from single crystals of Alnico is an obvious solution. Two known methods of producing single crystals sufficiently large to be of practical value are described, and the obvious economic and production problems discussed. New work on a third method is described in which normal foundry techniques are used, but the formation of a single monocrystal of the entire magnet is promoted by secondary recrystallization. It is shown that if a sufficiently large grain edge strain can be induced in a polycrystalline aggregate, resulting in secondary recrystallization, formation of a single large crystal is possible. It is also shown that if a sufficiently large internal stress can be introduced by both mechanical and thermal means, the required grain‐edge shift can be accomplished. The additions of normally prohibitive amounts of either carbon, nitrogen, manganese, or other ``gamma‐phase'' promoting elements will serve to provide the necessary mechanical strain, and methods of controlling their effect on the magnetic results are shown. The thermal stresses are accomplished by a simple maintainance of 60–80°C gradient across the magnet poles. This process has yielded single crystals approaching ¼ lb in size whose energy product is 11.0 megagauss‐oe. The practical nature of this process is discussed, and possible mass production techniques outlined.

ISSN:0021-8979    

DOI:10.1063/1.1728707

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The Preisach diagram calculated for an assembly of &ggr;‐Fe2O3particles at a packing density of 20% by volume has been used to obtain a distribution function of the particle remanence‐coercivities in the absence of interaction fields. This function, which has a peak at 275 oe, is then compared with the function obtained by differentiating the remanence hysteresis loop, i.e., with the distribution function in the presence of interaction fields. It is found that the latter function is broader than the former; this can be qualitatively explained in terms of a two‐particle model for the interacting particles. The magnitude of the interaction fields can be estimated from the Preisach diagram and is found to have a maximum value of roughly 300 oe.

ISSN:0021-8979    

DOI:10.1063/1.1728708

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Two years ago remarkable properties were reported for a new alloy based on manganese and aluminum. The value for saturation magnetization in Mn&dblbnd;Al had been extrapolated to infinite magnetizing field and was given as 6200 gauss. Our measurements indicate that the extrapolated figure is too low. Magnetization values of over 7100 gauss have been measured at 13 000 oe. Extrapolations of these values to infinite fields are not made because of anomalies in the magnetization curves at 7500 oe and 12 000 oe. The material having the high magnetization had an energy product of 4.0×106gauss oe.To reach the high values, it was necessary to adhere to processes and procedures having narrow limits. Saturation magnetization depended directly on composition, homogenizing, quenching rate, annealing, and deformation. The latter was most critical because a preferred axis of orientation is developed by this process. Mn&sngbnd;Al is very brittle, but the brittleness problem was circumvented by swaging the material in suitable jackets.Rockwell tests indicate that hardness is directly related to 4&pgr;M.

ISSN:0021-8979    

DOI:10.1063/1.1728709

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Electrodeposited Co&sngbnd;P films have been prepared having coercivities of 1000 to 1300 oe in the plane of the film. The material has been studied by means of x‐ray diffraction, electron microscopy, and the Craik technique. It is concluded that the material has a rod‐like structure and that shape anisotropy is at least partially responsible for the observed coercivity. The magnetic properties of this material are compared with those of previously reported platelet materials. An attempt is made to explain the properties of both rod and platelet materials on the basis of single domain particle theory.

ISSN:0021-8979    

DOI:10.1063/1.1728710

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Measurements of the anisotropy distribution in BaFe12O19were carried out using the remanent torque technique. Two randomly oriented powder samples with coercive forces of 1500 and 4000 oe were tested. The remanent torque curves for both samples were essentially identical indicating an anisotropy distribution with an average of 2.1±0.2×106ergs/cm3compared with a value of 3.3×106ergs/cm3for single crystal BaFe12O19. The origin of this disagreement is unclear but it seems to be associated with splitting into domains.

ISSN:0021-8979    

DOI:10.1063/1.1728711

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An investigation of the phase relations of the section Fe2P&sngbnd;Co2P in the system Fe&sngbnd;Co&sngbnd;P showed that at high temperature all (Fe, Co)2P alloys, including the final components Fe2P and Co2P, probably form a continuous range of solid solutions having the hexagonal Fe2P structure. At low temperatures Fe2P and Co2P form an almost complete range of solid solutions with the orthorhombic Co2P lattice. The Curie temperature of the hexagonal phase increases from about room temperature for Fe2P to a value of nearly 190°C for (Fe, Co)2P with an Fe:Co ratio of 70:30. The anisotropy fieldHAappeared to be a function of the Fe:Co ratio and possesses a maximum value of about 19 000 oe near an Fe:Co ratio of 90:10. Particles obtained by lixiviating an Fe&sngbnd;Co&sngbnd;Cu&sngbnd;P melt can possess a coercivityIHCup to 2000 oe. This value can be substantially increased by annealing. The temperature coefficient ofIHCappears to be relatively large and seems to be linked to the change ofKwith temperature. The coercivity decreases appreciably after mechanical loading, e.g. pressing, but can be restored by annealing; the anisotropy fieldHAas well as the saturation magnetization &sgr;∞changes in the same sense. Anisotropic permanent magnets have been made with aBHmaxvalue of about 2×106gauss oe.

ISSN:0021-8979    

DOI:10.1063/1.1728712

出版商:AIP    

年代:1962

数据来源: AIP