Magnetization and specific heat ofTbFe3(BO3)4: Experiment and crystal-field calculations

Abstract

We have studied the thermodynamic properties of single-crystalline TbFe3(BO3)4. Magnetization measurements have been carried out as a function of magnetic field (up to 50 T) and temperature up to 350 K with the magnetic field both parallel and perpendicular to the trigonal c-axis of the crystal. The specific heat has been measured in the temperature range 2-300 K with a magnetic field up to 9 T applied parallel to the c-axis. The data indicate a structural phase transition at 192 K and antiferromagnetic spin ordering at TN ≈ 40 K. A Schottky anomaly is present in the specific heat data around 20 K, arising due to two low-lying energy levels of the Tb 3+ ions being split by f-d coupling. Below T N magnetic fields parallel to the c-axis drive a spin-flop phase transition, which is associated with a large magnetization jump. The highly anisotropic character of the magnetic susceptibility is ascribed mainly to the Ising-like behavior of the Tb 3+ ions in the trigonal crystal field. We describe our results in the framework of an unified approach which is based on mean-field approximation and crystal-field calculations.

Nonresonant x-ray magnetic scattering on rare-earth iron boratesRFe3(BO3)4

“…"Heavier" rare-earth ions from Eu to Yb, and also Y cause a symmetry reduction to space group P3 1 21 upon lowering temperature which is manifested as a sharp peak at the transition temperature in specific-heat measurements. 1,3,13 The transition temperature T S depends basically on the size of the R-type ion present in the structure 6 and one observes a decreasing T S by increasing the R radius. In particular, one finds T S = 201.5 K, 155 K, and 445 K for the Tb-, Gd-, and Y-based compounds, respectively.…”

“…In addition, a rich variety of interesting structural and dielectric properties has been observed in these materials, partially coupled to the systems' magnetism, which is evidenced by a plethora of structural and magnetic phase transitions which depend on the rare-earth ion. [1][2][3][4][5][6][7][8] Furthermore, magnetoelectric coupling and multiferroic features, i.e., the coexistence of elastic, magnetic, and electric order parameters have been reported for the Nd-and Gdbased compounds. [8][9][10][11] At room temperature RFe 3 ͑BO 3 ͒ 4 compounds crystallize in the space group R32.…”

“…14 Regarding magnetic ordering, several interesting features are present in these materials. Previous measurements of magnetization, 3 specific heat, 1 and other techniques such as Mössbauer 15 spectroscopy and infrared absorption spectroscopy 16 have revealed a second-order antiferromagnetic ͑AFM͒ ordering transition of the iron sublattice at low temperatures ͑in the range ϳ30-40 K͒. The orientation of the Fe moments depends on the rare-earth ion present in the structure.…”

“…Furthermore, a firstorder magnetic phase transition is present in the Tb, Dy, and Gd compounds, where the antiferromagnetically ordered iron moments undergo a spin flop from the easy-axis state along the c direction to an easy-plane one along the ab plane when a magnetic field along the c axis is applied at low temperature. 3,20 In the case of TbFe 3 ͑BO 3 ͒ 4 the Fe spin flop is accompanied by a reconfiguration of the Tb moments from an antiparallel to a parallel arrangement ͓cf. Fig.…”

Probing magnetostructural correlations in multiferroicHoAl3(BO3)4

“…It has been found that the polarization along the a and c axes are related to the magnetic field induced ordering at the Fe and Ho sites, respectively. This behavior is not observed in the R = Y, Er [27], and Tb systems [28].…”