No abstract

The multicritical behavior of the Blume-Capel model with infinite-range interactions is investigated by introducing quenched disorder in the crystal field i , which is represented by a superposition of two Gaussian distributions with the same width σ , centered at i = and i = 0, with probabilities p and (1 − p), respectively. A rich variety of phase diagrams is presented, and their distinct topologies are shown for different values of σ and p. The tricritical behavior is analyzed through the existence of fourth-order critical points, as well as how the complexity of the phase diagrams is reduced by the strength of the disorder.

We calculate the diamagnetic susceptibility in zero external magnetic field above the phase transition from ferromagnetic phase to phase of coexistence of ferromagnetic order and unconventional superconductivity. For this aim we use generalized Ginzburg-Landau free energy of unconventional ferromagnetic superconductor with spin-triplet electron pairing. A possible application of the result to some intermetallic compounds is briefly discussed.Comment: 7 pages, 1 figur

The phase transition of the quantum spin-1/2 frustrated Heisenberg antiferroferromagnet on an anisotropic square lattice is studied by using a variational treatment. The boundaries between these ordered phases merge at the quantum critical endpoint (QCE). Below this QCE there is again a direct first-order transition between the AF and CAF phases, with a behavior approximately described by the classical line α c λ/2.