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A spin-one Ising model with biquadratic exchange interaction is investigated within a functional integration approach. The phase diagram is analyzed by means of Landau's free energy expansion. The dependence of the features of the system on the ratio of bilinear to biquadratic exchange interaction constants is discussed. In the random phase approximation, expressions for phase transition temperatures and the tricritical point for the ferromagnetic transition are obtained. Mogenb k l 3 l i H r a C 6MKBaupaTHbIM 06MeHHbIM B3aIlMOAekTBMeM (UnH s = 1) Kiy%XTCX B PaM-KaX MeTOAa @YHK4XOHaJIbHOrO MHTerpMpOBaHMX. @a30BaH RMarpaMMa aHa.JlH3Up)'eTCX IIpM IIOMOWli pa3JlOXeHHH . b H u a y CBO6OuHOfi 3HePrMli. PaCCMOTpeHa 3aBMCMMOCTb CHCTeMbI OT OT-HOIIIeHIllI B e n H W H 6 w n u~e i~o r o M 6 M K B a~p a T H O r O 06MeHHbIX B3aHMORekTBHb. B npn6nme-TMW3CKOJ% TOgKIl @eppOMarHMTHOrO IIepeXOUa.

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