PHASE-DIAGRAMS FOR DIAMAGNETIC PHASE-TRANSITIONS IN 2-DIMENSIONAL CONDUCTORS

We consider under conditions of the nonlinear de Haas-van Alphen effec t temperature-magnetic-field (T-B) phase diagrams for diamagnetic phas e transitions into homogeneous single-domain state in two-dimensional (2D) conductors and superconductors (i.e., with cylindrical Fermi surf ace) to estimate the T-B regions where magnetoquantum oscillations are strongly distorted by magnetic interactions. A universal relation is obtained between maximal transition temperature T-dm and cyclotron mas s m(c) at a given magnetic induction B-dm: (h) over bar omega(c) = Q(m )k(B)T(dm) with Q(m) = 5.45. Simple expressions are derived for maxima l transition temperature T-dm corresponding field B-dm, and limiting f ield B-0 (above which the transition does not occur at any temperature ), via Ferrni energy, cyclotron mass, and geometrical factors (lattice constant in anisotropic direction c and demagnetizing coefficient). Phase diagrams are drawn for characteristic parameters of the nearly 2 D organic conductors and superconductors of the (ET)(2)X type.