Tetracritical points in mixed magnetic crystals

Recently developed renormalization-group techniques are used to study the tetracritical (or bicritical) point of quenched mixed magnetic crystals (e.g., ApB1-p, where A and B have ferromagnetic and antiferromagnetic phase transitions). The tetracritical (bicritical) exponents are possibly given by the n=0 value of their ε expansions. In particular, the crossover exponent, describing the shape of the p-T phase diagram near the tetracritical point, is exactly equal to 1. This explains various experiments.