Phase diagram of a dilute ferromagnet model with antiferromagnetic next-nearest-neighbor interactions

الأصل · EN

We have studied the spin ordering of a dilute classical Heisenberg model with spin concentration x, and with ferromagnetic nearest-neighbor interaction J₁ and antiferromagnetic next-nearest-neighbor interaction J₂. Magnetic phases at absolute zero temperature T = 0 are determined examining the stiffness of the ground state, and those at finite temperatures T ≠ 0 are determined calculating the Binder parameter gₗ and the spin correlation length ξₗ. Three ordered phases appear in the x-T phase diagram: (i) the ferromagnetic (FM) phase; (ii) the spin glass (SG) phase; and (iii) the mixed (M) phase of the FM and the SG. Near below the ferromagnetic threshold x F, a reentrant SG transition occurs. That is, as the temperature is decreased from a high temperature, the FM phase, the M phase and the SG phase appear successively. The magnetization which grows in the FM phase disappears in the SG phase. The SG phase is suggested to be characterized by ferromagnetic clusters. We conclude, hence, that this model could reproduce experimental phase diagrams of dilute ferromagnets FeₓAu₁₋ₓ and EuₓSr₁₋ₓS.