Dynamics of structural and magnetic phase transitions in ferroborate YFe3(BO3)4

X-ray analysis of the YFe3(BO3)4 single crystal revealed different behavior of parameters of the crystal cell with an increase in temperature from 25 to 500 K. The parameters a and b initially increase monotonically and then rise sharply in the range between 360 and 380 K, which corresponds to the structural phase transition. The parameter c initially decreases linearly upon heating and then begins to increase, passing through a minimum at 90 K. In the interval of 200–500 K the parameter c grows linearly and does not undergo anomalies at the structural phase transition. The results of Mossbauer measurements at 57Fe nuclei in the paramagnetic phase of YFe3(BO3)4 correlate well with the XRD data, but they do not separate the two structural states of iron ions Fe1 and Fe2 arising in the P3121 phase during the structural phase transition. The temperature of the magnetic phase transition TN = 39.42(16) K is established, below which the iron ions form a 3D magnetic order of the Heisenberg type. The calculated “Mossbauer” Debye temperature ΘM = 340(2) K turned out to be three times lower than the Debye temperature of the entire crystal lattice TD = 1020 K. Mossbauer data indicate a weak bonding between the helicoidal chains of iron and the rest of the crystal lattice.