We demonstrate a scheme for coherently induced grating based on a mixture of two three-level atomic species interacting with two standing-wave fields.As a result of interaction between the absorptive and amplified Raman resonances,the refractive index of the medium can be enhanced and modulated periodically.Then a sinusoidal grating,which can diffract the probe field into high-order directions,is coherently formed in the medium.The proposed scheme is theoretically investigated in a mixture of atomic isotopes of rubidium.The results show that the diffraction efficiency depends strongly on the two two-photon detunings of the two Raman transitions and the intensities of the two driving standing-wave fields.The proposed electromagnetically induced grating scheme may be applied to the all-optical switching and beam splitting in optical networking and communication.