CONTINUOUS VERSUS FIRST-ORDER TRANSITIONS IN COMPRESSIBLE DILUTED MAGNETS

The interplay between disorder and compressibility in Ising magnets is studied. Contrary to pure systems in which a weak compressibility dri ves the transition first order, we find from a renormalization group a nalysis that it has no effect on disordered systems which keep undergo ing continuous transition with rigid random-bond Ising model critical exponents. The mean field calculation exhibits a dilution-dependent tr icritical point beyond which, at stronger compressibility, the transit ion is first order, The different behavior of XY and Heisenberg magnet s is discussed.