ANOMALOUS HALL-EFFECT IN GRANULAR ALLOYS

A theoretical study is performed of the anomalous Hall effect in granu lar alloys with giant magnetoresistance. The calculation is carried ou t within the Kubo formalism and the Green's function method. The mecha nism of asymmetric scattering of the spin-polarized current carriers i s considered with allowance for a size effect associated with scatteri ng not only by one grain, but also with more complicated processes of transport among two and three grains. It is shown that scattering of c onduction electrons by the interfaces of the grains and the matrix has a substantial effect on the magnitude of the anomalous Hall effect an d determines its sign. In general, correlation between the quantities rho(H) and rho(2) is absent, where rho(H) is the Hall resistivity and rho is the total resistivity of the granular alloy. However, numerical calculation shows that for certain values of the model parameters rho (H)-rho(3.8) and for these same parameter values the amplitude of the giant magnetoresistance reaches 40%, which is found to be in quantitat ive agreement with the experimental data for Co20Ag80 alloys [P. Xiong , G. Xiao, J. Q. Wang et al., Phys. Rev. Lett. 69, 3220 (1992)]. It is also shown that increasing the resistivity of the matrix leads to a s ignificant growth in the anomalous Hall effect, and mon substantial gr owth for alloys with small grain size, which is in good agreement with experiment [A. B. Pakhomov, X. Yan, and Y. Xu, J. Appl. Phys. 79, 614 0 (1996); [X. N. Jing, N. Wang, and A. B. Pakhomov, Phys. Rev. B 53, 1 4032 (1996)]. (C) 1997 American Institute of Physics. [S1063-7761(97)0 2012-X].