Bicritical and tetracritical behavior of GdAlO3

We have experimentally investigated the phase diagram of antiferromagnetic GdAlO3 near its spin-flop multicritical point (TM,HM) in the three-dimensional space spanned by the uniform fields H and H and the temperature T. In the H-T plane, (TM,HM) appears as a bicritical point, but as a tetracritical point in the H-T plane. The approach of all six boundaries to (TM,HM) is described by a single exponent ψ=1.17±0.02. This implies crossover exponents =1.17±0.02 and v=±0.03 in excellent agreement with renormalization group theory. © 1977 The American Physical Society.