摘要:

The microstructures of Ticonal G and Ticonal X in the condition of optimum magnetic properties are studied by the electron microscope using the direct carbon replica. It is argued that a very critical and extensive checking of results is essential in order to arrive at reliable conclusions. Work along these lines demonstrates that: (a) The main structural patterns for Ticonal G and X are the same; (b) the details of the structure of Ticonal G and X differ strikingly with respect to texture, width, length‐to‐width ratio, delineation and intergrowth; and (c) the influence of the magnetic field during cooling on the structure of Ticonal G on a plane ∥Hucan be shown directly.It cannot yet be decided whether the structure in the optimum condition is a true two‐phase structure or a single‐phase structure with periodic fluctuations in composition.It is possible that the dimensions revealed by etching do not represent those of the magnetic areas.

ISSN:0021-8979    

DOI:10.1063/1.1723107

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Improved electron microscope observation technique has confirmed some of the basic assumptions on the structure of Alnico V and has added knowledge of details. The permanent magnet precipitate was investigated at various states of its growth starting from nucleation. Pictures with details smaller than 20 A reveal the completely developed structure of Alnico V which differs somewhat from former descriptions. It can be recognized clearly that the precipitated particles have grown together to a continuous anisotropic network subdividing the matrix.Colloid patterns on these surfaces have been observed with electron microscope. During the reversal of magnetization, an anisotropic structure in the colloid‐covered areas of the pattern can be distinguished. The colloid particles align themselves, preferring one of the two faces of the precipitated structure. This is most pronounced in the steep part of the demagnetization curve. It can be observed as soon as the colloid starts to form patterns.The necessary surveying of magnet surfaces was possible by preparing very thin oxide replicas with a simple technique that eliminated the former ``floating'' method. Replicas were stripped from the surface which preserved the orientation without destroying the surface of the magnet.

ISSN:0021-8979    

DOI:10.1063/1.1723108

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

A magnetic analysis of the composition of the two Alnico V phases is tried. Structure‐independent properties, like saturation magnetization and temperature coefficient, serve to indicate the correctness of alloys supposed to represent these phases. A model of the two‐phase structure of Alnico V is derived from electron micrographs. The combined saturation magnetization and the combined temperature coefficients are calculated with this model using the measured properties of the single alloys. The two alloys whose combined properties come closest to those of Alnico V consist mainly of NiAl and Fe2Co, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1723109

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The physical and magnetic properties of permanent magnets compacted from elongated single‐domain particles with metal and organic matrices are described. Their unique properties which make possible novel design and application possibilities include: demagnetization curve flexibility; high‐energy and energy‐to‐weight ratio; uniformity of pole face flux; low‐temperature coefficient of remanence; precise dimensional tolerances; excellent machinability; solderability; low critical material content; and short radioactive half‐life. Compacts have been prepared from iron and iron‐cobalt particles with energies of 3.5 million and 5 million gauss‐oersteds, respectively. Compacts exposed to 200°C for over one year were observed to change remanence less than 1%.

ISSN:0021-8979    

DOI:10.1063/1.1723110

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Problems inherent to magnetic alignment of alpha iron crystals are discussed and explained by electron microscopic observation of the behavior of the single domain crystals under the effect of magnetic fields. With these specimens, which possess a fraction of magnetically unfavorable dendrites, intrinsic coercive forces of over 1700 oersteds have been measured without alignment.``By no endeavour can a magnet ever attract a silver churn''(W. S. Gilbert:Patience, Act II).

ISSN:0021-8979    

DOI:10.1063/1.1723111

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Experiments with spherical iron particles 28 A to 265 A in diameter demonstrate that the proposed nonferromagnetic surface layer on an iron particle must be less than 1 A thick, i.e., about one atomic radius. This conclusion is based upon a comparison of the ferromagnetic iron calculated from the magnetic saturation, and the total amount of iron as determined by chemical analysis. The 1/Hextrapolation of the magnetic induction appears adequate to obtain the saturation induction at room temperature of particles greater than about 100 A in diameter. For particles less than this size, in the superparamagnetic size range, the Langevin function must be used taking into account the size distribution of the particles in the sample. Thus there will be a negligible decrease in saturation induction due to the loss of exchange coupling at the surface of iron particles in the size range above 100 A of interest for fine‐particle permanent magnets.

ISSN:0021-8979    

DOI:10.1063/1.1723112

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The dependence of the ferromagnetic resonance upon specimen anisotropies (shape and magnetocrystalline) is well known. Observations of the ferromagnetic resonance absorption of submicroscopic particles may be interpreted to yield useful information about these anisotropies. The alloy 2% Co&sngbnd;Cu heat treated to precipitate cobalt containing about ten percent copper from the nonmagnetic solid solution has been studied using ferromagnetic resonance techniques. In the early stages of growth the precipitate particles are shown to be essentially spherical in shape. Further growth of the precipitate particles (by subsequent heat treatment) is accompanied by aspherical shape changes which modify the resonance spectra. The magnetocrystalline anisotropy of the cobalt precipitate in single crystals of this alloy has been determined. This anisotropy is cubic withK1/Ms=−665 oe at room temperature. The cobalt‐rich precipitate retains its cubic crystal structure to at least 4.2°K, apparently stabilized by the copper matrix.

ISSN:0021-8979    

DOI:10.1063/1.1723113

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

By demagnetizing a magnetic powder specimen with diminishing alternating fields of various initial amplitudes and by interpreting the results with the Stoner‐Wohlfarth model, one can obtain information about the shape distribution of the particles. We have done this with powders of acicular &ggr;‐ferric oxide at various temperatures; the temperature variation of the results gives information about the size distribution. The sample is first magnetized to saturation; the diminishing ac field is then applied and the remanence measured.Since the particles are not aligned along the applied field, it is necessary to get the equivalent magnetization curve for an aligned sample by operating on the data mathematically. The results indicate that only a small volume fraction of the &ggr;‐ferric oxide particles are small enough to be a paramagnetic. There is a relatively large volume fraction of particles with nearly zero critical field. We believe this is caused by particles which change their magnetization by a mechanism different from the Stoner‐Wohlfarth uniform rotation.On a volume basis, the shape distribution curves peak at a length‐to‐diameter ratio of about 1.6:1, which gives a coercive force of 300 oersteds. The coercive force agrees very well with measured values. The length‐to‐diameter ratio does not agree with electron microscopic observations, which give a mean of about 5:1.

ISSN:0021-8979    

DOI:10.1063/1.1723114

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

In the systems Au&sngbnd;Ni and &bgr;‐brass‐Fe, ferromagnetic precipitate particles develop in a nonmagnetic matrix. Single crystal samples of these alloys have been examined by measuring saturation magnetization, torque curves, rotational hysteresis, and remanence.The data on the Au&sngbnd;Ni system have been analyzed to infer particle anisotropy distributions, orientation of the ``easy'' axes of the particles, and other features of the precipitate particle system. Electron micrographs of the precipitate particles are in general agreement with this analysis. The measurements on the &bgr;‐brass‐Fe system indicated that the precipitate particles were single crystals with the same crystal habit as the matrix, and were elongated in the ⟨111⟩ directions. The temperature dependence of the torque curves was identified with the temperature dependence of shape and magnetocrystalline anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.1723115

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

In an alloy containing 2% cobalt, balance copper, it is possible to quench a nonmagnetic solid solution from 1000°C and then produce a ferromagnetic precipitate in a nonmagnetic matrix by aging at several hundred degrees. The magnetic properties of this precipitate can be correlated with the size and shape of the precipitate particles. Considerable information about the precipitation process can be obtained in this way. In these experiments, saturation magnetization, torque, rotational hysteresis, remanence, coercive force for zero magnetization, and coercive force for zero remanence (which behaves in a surprising fashion) have been observed during the course of aging. In particular, the effect of a field during aging in producing magnetic anisotropy (``magnetic annealing'') has been studied and is shown to occur entirely during the growth of the particles, after the precipitation is complete.The precipitation process is viewed as one in which the particles as they grow are first superparamagnetic, then stable single domains, and finally multidomain. This point of view is consistent with all of the varied phenomena observed.

ISSN:0021-8979    

DOI:10.1063/1.1723116

出版商:AIP    

年代:1958

数据来源: AIP