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The Faraday rotation (FR), magnetic circular dichroism (MCD), magnetic linear dichroism (MLD) and nuclear magnetic resonance (NMR) have been studied in the transparent ferrimagnet RbNiF3 (TC = 139°K). It was found that MCD and asymmetric anomalous dispersion of FR may be explained by the exchange splitting of electronic states of Ni2+ ions below TC. The structure and the temperature dependence of MCD of A23→1Ea transition confirms the model of magnetic structure with two unequivalent antiferromagnetically aligned sublattices. For the first time on the basis of NMR results the existence of two oppositely directed sublattices at temperatures about 100° above TC was observed in external magnetic field. The magnetization of one sublattice changes sign at T≃270°K.

The static magnetic properties of a single crystal of NaNiF, (space group PI,-) are invest,igated in the temperature range 77 to 300 OK. The Nbel temperature, TN = 156 OK, is determined and the temperature dependences of the magnetic susceptibilities along different crystallographic directions are investigated. The spontaneous magnetic moment is observed only along the c-axis in fields of up to 18 kOe a t 77 OK. The results obtained are discussed within the framework of the thermodynamic theory of weak ferromagnetism.The anisotropic superexchange appears to be most probable mechanism for the origin of weak ferromagnetism in NaNiFr A departure of the temperature dependence of the spontaneous moment from the respective Brillouin function is observed. (npocTpaHcTseHHasx rpynna P b m ) B m-rrepsane TeMnepaTypOT 77 no 300°K. OnpeEeneHa Tenmepa-rypa Heensi T N = 156 "K, II 1133n1e~b1 TeMnepaTypHare I/ICcJIeAOBaHbl CTaTIIYeCKUe MarHUTHbIe CBOfiCTBa MOHOKpIICTaJIJIa NaNiF, 3aBWCUMOCTH MarHIITHbIX BOCnPHUMWiBOCTefi BAOJIb pa3JlElqHbIX KpIICTaJIJlOrpa-(PW9eCKWX HaIIpaBneHUfi. CnOHTaHHbIfi MarHHTHbIfi MOMeHT B IIOJIRX EO 18 K 3 IIpM 77 H~~J I I O J I~~T C R TOJlbKO BAOJlb OCU C. fl0JIyYeHHHe pe3yJIbTaTbI 06cym AaIoTCR B PaMKaX TePMOAHHaMHYeCKOfi TeOPHII ma60ro (PeppOMarHeTW3Ma. no-Ka3aH0, YTO na116onee BepORTHbIM MeXaHU3MOM B03HHKHOBeHIIR cna6oro (PepPo-MarHeTU3Ma B NeNiF, RBJIIIeTCfl aHH30TpOIIHblfi CBepXO6MeH. OTMeYaeTCfi OTKJIO-HeHIIe TeMnepaTypHOfi 3aBWCWMOCTH CIIOHTaHHOrO MOMeHTa OT COOTBeTCTByIoIQefi @YHKUAII Epunn~oa~a.

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