New line of thermodynamic phase transitions on the x-T diagram of a dilute Heisenberg system with short-range interactions Li0.5Fe2.5-xGaxO4

It is established on the basis of an investigation of the temperature dependences of the saturation magnetization sigma(S)(T) and the magnetic contribution to the specific heat C-m(T) that in the reentrant region of the x-T diagram (0.9 less than or equal to x less than or equal to 1.5) of dilute iron spinels Li0.5Fe2.5-xGaxO4 there exists between the line of Curie points T-C(x) and the line of freezing temperatures T-f(x) another line of first-order phase transitions T-1(x) to a noncollinear ferrimagnetic phase: T-C(x)less than or equal to T-1(x)less than or equal to T-f(x). (C) 1998 American Institute of Physics. [S0021-3640(98)00905-0].