We investigate the spin-dependent transmission through an Aharonov-Bohm ring with a quantum gate that is tuned by an uniform external magnetic field. The formula of spin-dependent transmission coefficient at zero temperature is obtained as a function of the flux, the magnetic field and Fermi energy in term of quantum waveguide theory. We found that for some special Fermi energies, spin-state electrons are driven into a perfect transmissive state or reflective state, which is not affected by the flux, when Zeeman energy of electron moving in the stub coincides with a level of the isolated stub. As Zeeman energy crosses the level of the stub, Aharonov-Bohm oscillations of spin-state conductance have no abrupt change of phase by pi and are in phase. The effect of the magnetic field on transmission behavior of spin-state electrons are examined. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 16]
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