Strongly asymmetric tricriticality of quenched random-field systems

In view of the recently seen dramatic effect of quenched random bonds on tr icritical systems, we have conducted a renormalization-group study on the e ffect of quenched random magnetic fields on the tricritical phase diagram o f the spin-1 Ising model in d = 3. We find that random fields convert first -order phase transitions into second-order phase transitions more effective ly than random bonds. The coexistence region is extremely flat, attesting t o an unusually small tricritical exponent beta(u). The random-field phase d iagram is strikingly asymmetric. To accommodate this asymmetry, the second- order boundary exhibits reentrance. [S0031-9007(99)08751-7].