D. V. Volkov

Magnetization and specific heat of TbFe3"BO3…4: Experiment and crystal-field calculations

ions inthe trigonal crystal field. Our experimental data are analyzedin the context of the unified approach which is based onmean-field approximation and crystal-field calculations. Thespin-flop transition is apparently accompanied by magneto-elastic effects. Magnetoelectric effects might therefore be as-sociated with the spin-flop transition, leading TbFe

Magnetic properties of HoFe 3 (BO 3 ) 4

The magnetic properties of an antiferromagnet with trigonal symmetry, namely, HoFe3(BO3)4, have been investigated theoretically. The calculations have been performed in the molecular field approximation and in the framework of the crystal field model for the rare-earth subsystem. Extensive experimental data on the magnetic properties of HoFe3(BO3)4 have been interpreted and good agreement between theory and experiment has been achieved using the obtained theoretical dependences. The spontaneous spin-reorientation transition and the spin-reorientation transition induced by a magnetic field B ‖ a from the easy-axis to easy-plane state, as well as the spin-flop transition in a magnetic field B ‖ c, have been described. It has been shown that the spontaneous spin-reorientation transition is a magnetic analog of the Jahn-Teller effect. The temperature dependences of the initial magnetic susceptibility at temperatures ranging from 2 to 300 K, the nonlinear curves of magnetization for B ‖ c and B ⊥ c in a magnetic field up to 1.2 T (which indicate the occurrence of first-order phase transitions), and their evolution with variations in the temperature have been described, as well as the temperature and field dependences of the magnetization in a magnetic field up to 9 T. The parameters of the trigonal crystal field for the rare-earth ion Ho3+ and the parameters of the Fe-Fe and Ho-Fe exchange interactions have been determined in the course of interpretation of the experimental data.

Magnetic properties of an easy-plane trigonal NdFe3(BO3)4 antiferromagnet

The field and temperature dependences of magnetization and the temperature dependences of the initial magnetic susceptibility have been theoretically studied for three crystallographic directions in a trigonal NdFe3(BO3)4 antiferromagnetic crystal. The calculations were performed using a molecular field approximation and a crystal field model for the rare-earth subsystem. The obtained theoretical expressions are applied to the interpretation of recent experimental data [1–4] on the magnetic properties of NdFe3(BO3)4. The results of calculations show a good agreement with experiment. The proposed theory adequately describes (i) anomalies of the Schottky type in the temperature dependence of the magnetic susceptibility, (ii) nonlinear curves of magnetization in the basal plane in a magnetic field up to 1 T (showing evidence of the first-order phase transitions) and their evolution with the temperature, and (iii) the field and temperature dependences of magnetization in a magnetic field up to 9 T.

Magnetic properties of DyFe3(BO3)4

The magnetic properties of an easy-axis trigonal DyFe3(BO3)4 antiferromagnetic crystal have been theoretically studied. On this basis, recent experimental data [1] on the field and temperature dependences of magnetization and the temperature dependence of the initial magnetic susceptibility for three crystallographic directions in this antiferromagnet have been interpreted. The characteristics of the trigonal crystal field for the rare earth ion and the parameters of the Fe-Fe and Fe-Dy exchange interactions are determined. Limitations imposed by features of the magnetic characteristics (anisotropic magnetization in the three crystallographic directions, Schottky-type anomalies in the magnetic susceptibility, etc.) on the possible splitting of the ground-state multiplet in the crystal field and the splitting of the lowest doublet due to the f-d interaction for Dy3+ ions are established.

Magnetic properties of the rare-earth ferroborate SmFe3(BO3)4

The magnetic properties of trigonal antiferromagnet SmFe3(BO3)4 are studied experimentally and theoretically. The measured characteristics are considered in terms of a theoretical approach based on the molecular field approximation and a crystal field model for a rare-earth ion. The temperature dependences of the initial magnetic susceptibility and the field and temperature dependences of magnetization in fields up to 5 T are described, and the anomaly in the magnetization curve for B ⊥ c near 1 T, which points to a first-order phase transition, is analyzed.

Paradox of a nonlinear beam splitter and its resolution

A nonlinear beam splitter is shown to be an interesting object of investigation for the following reasons. First, the classical and quantum theories of its description give directly opposite behaviors of the phase fluctuations: according to the classical theory, the phase is unchanged; according to the quantum theory, the phase fluctuations increase or decrease, depending on the suppression or growth of amplitude fluctuations. The fundamental cause of these differences has been established. Second, the quantum fluctuations of the input mode can be separated into the amplitude and phase ones, so that the predominantly phase fluctuations are directed into one output mode, say, the reflected one, while the amplitude fluctuations are directed into the other (transmitted) mode.

Magnetostriction and thermal expansion of HoAl3(BO3)4

The magnetostriction and thermal expansion of rare-earth aluminoborate HoAl3(BO3)4 have been studied theoretically. The calculated field and temperature dependences of the multipole moments of the Ho3+ ion in HoAl3(BO3)4 made it possible to describe the known experimental data and to predict possible anomalies of thermal expansion. It has been shown that, for the direction of the field B ‖ c, the nonmonotonic character of magnetostriction along the axis a is determined by the multipole moments, the main of which is βJ 〈O40〉. For B ‖ a and B ‖ b, the maximum moments are βJ 〈O42〉and αJ 〈O22〉; their variation with the field and temperature explain well the form of magnetostriction. It has been established that the greater value of magnetostriction Δa/a for B ‖ b than for B ‖ a and the greater value of magnetostriction for the field in the basal plane than for B ‖ c are caused by greater variations in the field of actual multipole moments.

Magnetic, magnetoelastic, and spectroscopic properties of TmAl3(BO3)4

The thermodynamic properties of alumoborate TmAl3(BO3)4 single crystal are studied experimentally and theoretically. A theoretical analysis based on the crystal field model makes it possible to interpret all measured parameters. The crystal field parameters are determined. The temperature (3–300 K) and field (up to 9 T) dependences of magnetization are described. The field and temperature dependences of multipole moments of the Tm3+ ion in TmAl3(BO3)4 make it possible to describe magnetostriction and low-temperature anomalies in thermal expansion.

Magnetic Properties of Tb 1- x Er x Fe 3 (BO 3 ) 4 (x = 0.75, 1)

The magnetic properties of antiferromagnets with trigonal symmetry, namely, Tb1 − xErxFe3(BO3)4 (x = 0.75, 1), have been investigated theoretically. The calculations have been performed in the molecular field approximation and in the framework of the crystal field model for the rare-earth subsystem. For the Tb0.25Er0.75Fe3(BO3)4 antiferromagnet, the anomalies revealed in the magnetization curves measured during the spin-flop transition induced by a magnetic field B | c and their evolution with variations in the temperature have been described, as well as the temperature dependences of the initial magnetic susceptibility at temperatures down to 80 K. The existence of a low-temperature Schottky-type anomaly in the magnetic susceptibility curve for a magnetic field B | c has been predicted. For the ErFe3(BO3)4 system, the experimental data obtained for the magnetization in magnetic fields up to 15 T at temperatures ranging from 4.2 to 70 K, as well as the temperature dependences of the magnetic susceptibility at temperatures up to 350 K, have been interpreted. The description of the contribution from the rare-earth subsystem to the heat capacity of Tb1 − xErxFe3(BO3)4 (x = 0, 1) has allowed us to predict the character of the rare-earth contribution to the heat capacity of Tb0.25Er0.75Fe3(BO3)4.