ISSN:0021-8979    

DOI:10.1063/1.2185887

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

If an anisotropic local atomic configuration is produced in some way or other, the magnetization is stabilized in a direction related to this anisotropy, causing an additional uniaxial magnetic anisotropy. This kind of an anisotropy in the atomic configuration is called a directional ordering. This may be an anisotropic distribution of constituent atoms in substitutional ferromagnetic alloys, of interstitial atoms in a body centered cubic lattice, or of different atoms or ions on theBsites of mixed ferrites, etc. A brief explanation of the phenomena is given in each case. Also because of the coupling between the atomic arrangement and the direction of the magnetization, a relaxation phenomenon may be observed in the magnetization process which depends on the diffusion of atoms. The magnetic aftereffect arising from a small amount of carbon in &agr;‐iron is explained in detail.

ISSN:0021-8979    

DOI:10.1063/1.2185960

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

This paper presents a general review of the modern state of phenomenological theory of ferro‐ and antiferromagnetism and the results of some investigations of the authors in this field.

ISSN:0021-8979    

DOI:10.1063/1.2185984

出版商:AIP    

年代:1959

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.2185886

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

In aMe22+Sn4+O4spinel, Sn4+is known to occupy octahedral sites. Therefore manganese‐tin spinel,(Mn)[MnSn]O4, would be antiferromagnetic because of the strong interaction between octahedral and tetrahedral ions characteristic of magnetic spinels. The magnetic exchange interaction in a (Mn2+)‐O2−‐[Mn2+] linkage is of particular interest because it is known to be much weaker than is the case for Fe3+with which Mn2+is isoelectronic; magnetic measurements on slightly oxidized Mn‐Sn spinel yield a Ne´el temperature of 58°K.When the initial equality of the sublattice magnetizations of Mn2+ions in octahedral and tetrahedral sites is upset by substitution of nonmagnetic, divalent ions, Mg2+and Zn2+, for Mn2+, spontaneous magnetization appears. The Ne´el temperature is decreased by these substitutions largely as a consequence of the smaller number of interactions between the reduced number of Mn2+ions in the two different sites. For equal substitutions for Mn2+inMn2SnO4, the moment changes more rapidly in the case of Mg2+than Zn2+. The moment depends upon the size of the substituent ion because, in this case, the ions involved are spherical and of the same valence. A smaller size of these substituent ions leads to a greater predominance of occupation of the octahedral sites because substitution there increases the Madelung potential both by reduction of lattice constant and increase of oxygen parameter. The sequence, Mg2+, Zn2+, Mn2+, of increasing ionic sizes corresponds to that of increasing lattice constants, 8.60 8.67, 8.88 A, of the respective tin spinels. Substitution of Ge4+for Sn4+takes place principally in tetrahedral sites because of the very small size of Ge4+.Similarly, spontaneous magnetization appears with oxidation ofMn2SnO4. The resultant oxidized manganese ions (presumably Mn3+) are of the same average valence, though of smaller size, than the octahedral ions and, therefore, also appear in octahedral sites. Because Sn4+is rejected to maintain valence balance, the octahedral sublattice magnetization is increased by oxidation.

ISSN:0021-8979    

DOI:10.1063/1.2185892

出版商:AIP    

年代:1959

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.2185896

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The relations between sintering temperature, grain size, and magnetic properties of a manganese zinc ferrite of compositionMnO:ZnO:Fe2O3 = 28:19:53are reported. With proper preparation, very low loss materials can be obtained.

ISSN:0021-8979    

DOI:10.1063/1.2185902

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The concept of octahedral site preference energy in spinels has been extended to include Madelung and short‐ranged as well as crystal field terms. A set of site preference energies is formulated which can be used to predict the ionic distribution of spinels involving the nontransition as well as the transition ions. The agreement between predicted and experimentally determined ionic distributions is surprisingly good, and a number of heretofore puzzling distributions are explained.

ISSN:0021-8979    

DOI:10.1063/1.2185913

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The remagnetization time&tgr;has been measured as a function of external fieldHfor a series of manganese ferrites,Mn1+xFe2−xO4. The physical properties of these compounds which enter into the domain wall model of Menyuk and Goodenough and the rotational model of Gyorgy have also been measured. It is found that&agr;, the loss constant, is critical to the correlation of data with theory, and that neither theory can be unequivocally proved until more insight into the remagnetization process loss mechanism is acquired.

ISSN:0021-8979    

DOI:10.1063/1.2185924

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The most commonly offered interpretation of the low magnetic moments of chromium‐containing spinels has relied on the existence of the Yafet and Kittel ordering scheme. The experimental evidence for angular ordering schemes on theBlattice of spinels is, however, inconclusive and contradictory. Prince, for instance, has obtained neutron diffraction data onCuCr2O4which is consistent with, but does not uniquely determine, the Yafet‐Kittel scheme. Pickart, on the other hand, has found no evidence of the angular scheme in data on(MnFe2O4)1−x+(MnCr2O4)xand(NiFe2O4)1−x+(NiCr2O4)x, although he did establish that the moment of theBlattice was lower than expected on a simple Ne´el picture. In this report, we present a new approach to this problem which appears to lead to a reasonable, adequate, and consistent treatment of the moment data.It is usually supposed that the spin of the Cr3+ion in the octahedral environment of the spinelBsite is32giving a moment of three Bohr magnetons. A consideration of the crystal field theory pertinent to Cr3+shows, however, that if theBsite is given a sufficient tetragonal or trigonal distortion, the doublet state, having a spin of12and a moment of one Bohr magneton, becomes the ground state. It is known further that theBsites can be distorted from regular octahedral symmetry by the presence of Jahn‐Teller distortions in neighboring sites. For example, Ni2+and Cu2+cause distortions when onAsites, while Cu2+and Mn3+cause distortions when on theBsites. The process by which the moment of an ion is reduced in this way is called “spin quenching.”We therefore propose that the origin of the low moments in the chromites is the spin‐quenching effect imposed on the Cr3+ions by the appropriate Jahn‐Teller distortions of their neighbors. We also emphasize that a macroscopically distorted phase is not required for this effect. It is only necessary that a distribution of distorting neighbors be present, sufficient in number to alter the symmetry about (and hence spin quench) at least a fraction of the chromium ions. With the aid of these hypotheses it has proved possible to explain the moment data for many chromites in a consistent way. Of particular interest are the recently studied systems,(CuFe2O4)1−x+(CuCr2O4)xand(NiFe2O4)1−x+(NiCr2O4)x.

ISSN:0021-8979    

DOI:10.1063/1.2185931

出版商:AIP    

年代:1959

数据来源: AIP