Abstract

• Magnetic and heat capacity measurements are made near Curie temperature T C = 30.3 K. • Significant difference between T C and paramagnetic Curie temperature are observed. • Magnetic contribution to specific heat in zero field exists in great region above T C . • Inter- and intrachain exchange parameters are determined to differ 5 times. • Some peculiarities are found due to 1D character of magnetic structure. Near the Curie temperature T C = 30.3 K, the temperature dependences of the magnetization and heat capacity of a single-crystal ferromagnet PbMnBO 4 in the magnetic fields of 1, 3, 10 and 30 kOe are studied. In the strong magnetic fields, both the magnetic contribution to the specific heat and the nonlinearity of the field dependences of the magnetization are maintained up to the temperatures exceeding T C more than twice. It is assumed that in PbMnBO 4 the difference between T C , the paramagnetic Curie temperature θ = 49 K and the broad temperature region above T C where the magnetic contribution to the specific heat is significant is due to the quasi-one-dimensional character of the magnetic structure of this ferromagnet. Using both the estimation of T C from the Ginzburg-Landau field theory and the θ value, the total exchange interaction parameters 2 J ≈ 40.4 K (intrachain) and z ′ J ′ ≈ 8.8 K (interchain) are determined, with z ′ = 4 being the number of neighboring chains. The estimation shows that the Ginzburg-Landau field theory describing the quasi-one-dimensional behavior of PbMnBO 4 is well applicable in the temperature range from to T = S 2 J ≈ 80 K. Above this temperature, the mean field approximation with the exchange parameter λ θ based on the paramagnetic Curie temperature θ describes well the experimental temperature dependences of the magnetization in the strong magnetic field and the specific heat is determined by the lattice contribution.

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