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2023-01-16T04:03:09Z
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Spin wave spectrum and related problems for ferromagnetic 3 d-group transition metals and alloys
Yamada, Hideji
103120
1968-12-31
Calculations on temperature variations of the magnetizations for nickel and iron metals are performed by the Stoner theory. Exchange energy is expanded as a power series of the magnetization M and values of its coefficients are estimated from the comparisons between calculated and experimental results of the temperature variations of M for nickel and iron metals. In a phenomenological way, a new expression for the magnetic energy due to fluctuations of the magnetization density is found for an isotropic continuous ferromagnetic medium. By using the Holstein-Primakoff transformation, it is shown that many terms in this expression, except the term discussed by Herring and Kittel, correspond to spin wave-spin wave interactions. From the microscopic point of view, the dispersion relations of spin waves in ferromagnetic metals with multiple bands are obtained by the method of normal modes within the random phase approximation and a certain approximation for the Coulomb interaction. It is found that spin wave spectra consist of some branches; one acoustical intraband branch, one acoustical inter-band branch and some optical intra-and inter-band branches. The inter-band transitions have an important effect on the acoustical intra-band branch at larger momenta of spin waves. Within the (extended) random phase approximation, the equation of motion for normal modes in an electron gas is solved by the iteration method and the dispersion relations of a plasmon in the paramagnetic and ferromagnetic electron gases are obtained. It is shown that there is no difference between constant terms in the dispersion relation with respect to the momentum of a plasmon in the paramagnetic and ferromagnetic states, but coefficients of the terms proportional to the square of the momentum of a plasmon are different in the two states. High field susceptibilities for ferromagnetic iron metal and its alloys are estimated at 0°K, by making use of the density of states curve determined by the rigid band model. A satisfactory agreement between the calculated and observed results on the concentration dependences of high field susceptibilities at 0°K is obtained for iron-cobalt and iron-nickel alloys. The dependences on temperature and magnetic field of the high field susceptibility are calculated by the model of non-interacting free spin waves. The observed temperature dependence of the high field susceptibility is satisfactorily explained by the calculated result.
departmental bulletin paper
Faculty of Engineering, Nagoya University
1968-12-31
Memoirs of the Faculty of Engineering, Nagoya University
1
20
181
257
0027-7657
eng