Savina Y. Magnetic, thermal and resonance properties of the quasi-one-dimensional Heisenberg magnet β TeVO4

The thesis is devoted to the experimental study of magnetic phase transitions and the peculiarities of the magnetic and thermodynamic behavior of a quasi-one-dimensional magnet β TeVO4. The main results of the thesis have been obtained by using magnetometric methods of investigation in combination with calorimetric and resonance measurements. The β TeVO4 compound is found to be a quasi-one-dimensional magnet consisting of weakly interacting zigzag chains of V4+ ions (S = ½) with frustrated intrachain exchange couplings. It is shown that the phase H-T diagram of the magnet contains of four different spin-modulated states, which are described by an isotropic one-dimensional J1-J2 model with two competing interactions. It is found that the competition of ferromagnetic exchange between the nearest neighboring magnetic ions and antiferromagnetic exchange between the next-nearest neighboring magnetic ions determines the spin-modulated chiral phase as the ground state of β TeVO4. The weak axial anisotropy of the magnetic and resonant properties respect to b axes has been revealed. In the phase diagram for H||b a tricritical point has been found which is related to the spatial anisotropy of the ground state of β TeVO4.