Vol. 20, No. 9 (1964)
1964-05-05
CONTENT
THE MAGNETIC STRUCTURES OF CRYSTALS WITH MAGNETIC UNIT CELL UN-IDENTICAL WITH ITS CHEMICAL UNIT CELL
1964, 20 (9): 825-845.
doi: 10.7498/aps.20.825
Abstract +
In this work a phenomenological method is developed for the determination of spin configurations of magnetic crystals with a magnetic unit cell un-identical with its chemical unit cell. A finite group, formed of those elements of the space group which are distributed within a magnetic unit cell, is introduced. The expansion of the thermo-dynamic potential in terms of sublattice spin densities is constructed according to the principle that it should be invariant when symmetry operations of the above mentioned group are applied on sublattice spin densities separately. Spin configurations of magnetic crystals are then determined from the minimum condition of thermodynamic potential.With the above method, we have discussed the spin configurations of magnetic crystals of four different types. In each case, the results obtained are consistent with those of neutron diffraction experiments. Under certain conditions the existence of helical spin configuration may also be accounted for with the aid of this method.
1964, 20 (9): 846-862.
doi: 10.7498/aps.20.846
Abstract +
A new approximate method for treating nn and pp pairing force in nuclei is presented. In this method the difficulties connected with the application of BCS-Bogolubov method to nuclei such as the non-conservation of the number of particles, the apperance of spurious states, and non-orthogonality between wave functions of different excited states are avoided. But the method can be conviently adopted only when the number of particles n and the number of levels Ω considered are small (n ≤10, Ω≤10 ). Also the approximation of this method is good onlv under such conditions. In this method the many-body nature of the excitation is displayed explicitly without introducing the conception of quasi-particles. The excitation of the system can be divided into two classes. The first class of excitation is a kind of single particle excitation embedded in a many-body system under the action of the pairing force. This would correspond to the excitation of a single quasi-particle av+a(v0) or to two quasi-particle excitation of the type αv+βv′+,αv+αv′+(v′≠v) etc. in the BCS-Bogolubov method. The second class of excitation is a pair excitation in which the distribution of the conjugated pairs of particles among the levels is altered. This type of excitation would correspond to superposition of quasi-particle excitations of the type αv+βv+,αv+βv+αμ+βμ+, Also examined is the effect of pairing force on the β- and γ-transition probability in the new formalism. In general, β-transition is retarded by the pairing force while in γ-transition the effect of pairing force varies according to the nature of the relative excitation between the initial and final states. When the relative excitation is of the first class, the transition is retarded to various extent, depending on the nature of the γ-transition. If the relative excitation is of the second class, the transition is forbidden when the pairing force is not in action, and is allowed only for electric transition arising from the charge-current distribution when the pairing force is present. Finally this method is applied to investigate the effect of pairing force on the intrinsic spectra and β-transition in 72Hf178 as an example.
REGGE BEHAVIOUR FOR THE SCATTERING UNDER A POTENTIAL WITH A SINGULARITY AT ORIGIN HIGHER THAN z~(-2)
1964, 20 (9): 863-872.
doi: 10.7498/aps.20.863
Abstract +
Assuming that: (l), the potential V(z)→z-n(n>2) as z→0; (2), V is regular in Re z>0; (3), V(z)z2→0 as z→∞ in |arg z|<π/2, the following assertions are proved: (l), the scattering matrix element S is meromorphic in the whole λ plane (λ=l+1/2,l—angular momentum);(2)S-1→O((log|λ|)/|λ|) as λ→∞ in |arg λ|<π/2.
1964, 20 (9): 890-908.
doi: 10.7498/aps.20.890
Abstract +
The possible forms of the anisotropic interactions between d electrons in cubic ferro-magnets in the theory of the polar model of metals are studied. Their contributions to the magnetic anisotropic constant K1(T) are calculated based on Dyson's theory of spin wave interactions with the method of the statistical perturbation theory. The accuracy of the calculation is restricted to the first order of the coupling constants of anisotropic interactions, and the results are given up to the T4 terms. It is shown that K1(T) varies roughly as the tenth power of the spontaneous magnetization in the temperature range where the theory is reasonable.
1964, 20 (9): 909-918.
doi: 10.7498/aps.20.909
Abstract +
Internal friction in an iron-manganese alloy containing 18.5% Mn was measured by a torsion pendulum; a stable internal friction peak was observed within the temperature range for the direct as well as for the inverse martensitic transformation of this alloy. When measurement was taken in descending temperatures, the internal friction peak associated with the direct martensitic transformation appeared round 100℃; and that associated with the inverse martensitic transformation appeared round 200℃ when measurement was taken in ascending temperatures.Systematic studies were made on these two internal friction peaks after they became stable and they were found to have the following characteristic features:1. The position of the peak is independent of the vibration frequency used;2. The height of the peak increases appreciably with an increase of the strain amplitude used in the measurement of internal friction;3. With an increase of the number of cycles of heating and cooling given to the specimen, the position of the peak shifts to a temperature further apart from the initial transformation temperature, and the height of the peak decreases consecutively.The independence of the position of the peak on frequency indicates that the basic process giving rise to internal friction is not controlled by heat activation. The dependence of the height of the peak on strain amplitude indicates further that the mechanism of internal friction is not concerned with anelasticity. Observations by transmission electron microscopy have revealed that the stacking fault associated with an extended dislocation may serve as nuclei for martensitic transformation of the Fe-Mn alloy studied, so that the stable internal friction peaks observed may be associated with the stress-induced expansion and contraction of the extended dislocations in the specimen. Such a model can explain the internal friction phenomena observed in the Fe-Mn alloy in a unified manner.
1964, 20 (9): 919-927.
doi: 10.7498/aps.20.919
Abstract +
An instrument for measuring the first and second derivatives of l-V characteristics of tunnel diodes and point contact diodes as a function of D.C. bias was designed. The principle of operation is based on the harmonic analysis of the current. The circuit involved is rather simple. As an example for the application of this instrument, plots of first and second derivatives of a tunnel diode and a point contact diode were shown. From the given results, it has been pointed out that tunnel diodes may be used in low level detectors.
