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Neutron diffraction studies of a TlMnCl3 powder samples show that they are antiferromagnets of the G‐type with Néel temperature TN = (113 ± 5) K. The transition to the weak ferromagnetic state is observed at Tc = (110.5 ± 0.05) K by magnetic measurements. The magnetic susceptibility and the weak ferromagnetic moment of TlMnCl3 single crystals are found to be isotropic below the Néel temperature which is explained by twinning of the crystal. The twinning is removed by stressing the crystal along the [110] direction during cooling. The investigation of untwinned crystals allows to determine that the antiferromagnetic vector L lies in the [110] and the weak ferromagnetic moment in the [001] direction. The temperature dependences of the magnetic susceptibility and the weak ferromagnetic moment are investigated.

The helical magnet CsCuC1, in an applied field higher than the critical field is shown to have sinusoidal phase with linear polarization of spins. The new intermediate phase is due to a conical-point instability caused by weak dipole interactions. Therefore in different temperature ranges two modulated structures are actually realized. Results found theoretically are in good agreement with the experimental data. nOKa3aH0, YTO BO BHeZUHeM IIOJIe BbIIIIe KpElTHseCKOrO B reJIHIEOPiAaJIbHOM MarlieTElHe CSCUcl, BO3MOECHO IIOHBJIeHHe CHHyCOH~aJIbHOfi $la361 C JIElHeaHOt llOJIFfpH3aqHefi CIIH-HOB. Hosan llpOMeECyTOsHaH @a3a 06yc~10B~IeHa HeYCTOfiYHBOCTbH) KOHEl YeCKOH T O W 3 3 M3-3a cna601-0 ,li€XllOJIbHOrO B3aHMO~eBCTBHR. n O 3 T O M Y B pa3JIM4HbIX TeMlIepaTypHbIX BHTepBaJIaX @ICTLIYeCKM peaJIH3yIOTCFI ABe MOAyJIHpOBaHHbIe CTpYICTYPbI. HatAeHHbIe TeOpeTElYeCKH pe3yJIbTaTbI XOpOUIO COrJIaCYIoTCFf C 3KCIIepElMeHTaJIbHbIMM HaHHbIMEl.