Low-temperature structural and magnetic phase transitions in multiferroic GdFe3(BO3)4

X-ray analysis revealed that at temperature decreasing from room temperature to Tstr = 155 K the crystal unit cell GdFe3(BO3)4 is reduced only along the c axis (at 0.01 Å), while the a and b axes are unchanged within the error limits. The volume of the crystal decreases uniformly in the direction of all three axes at 155-80 K. At 80-30 K the crystal volume is decreased only by reduction of the parameters a and b, while the parameter c increases conversely. In the paramagnetic region Mössbauer spectra do not distinguish between the two structural positions of iron ions Fe1 and Fe2, appearing at T < Tstr. Below the temperature of the magnetic phase transition at TN = 38.0(1) K the Mössbauer data indicate quasi-one-dimensional magnetic ordering of iron moments in the sublattice Fe2 and a two-dimensional one in the iron sublattice Fe1. The dynamics of spin reorientation in sublattices Fe1 and Fe2 is studied in detail.