Microscopic model for the magnetic subsystem inHoNi2B2C

Abstract

We demonstrate that the system of localized magnetic moments in HoNi2B2C can be described by the 4-positional clock model. This model, at a proper choice of the coupling constants, yields several metamagnetic phases in magnetic field at zero temperature in full agreement with the experimental phase diagram. The model incorporates couplings between not nearest neighbors in the direction perpendicular to the ferromagnetic planes. The same model leads to a c-modulated magnetic phase near the Curie temperature. The theoretical value of the modulation wave-vector agrees surprisingly well with that observed by the neutron diffraction experiment without new adjustable parameters.In the works by Rathnayaka et al. In this compound easy magnetization axes are identified with crystallographic directions 110 and 110 . The low temperature magnetization data show the existence of 4 metamagnetic phases. The low field phase has been identified by neutron diffraction experiments [3,5] and magnetic measurements [2] with the antiferromagnetic phase, which we denote symbolically ↑↓. The phase boundaries and magnetization in other phases versus magnetic field found in the experiment [2] can be readily explained by assuming that the remaining three phases are as follows: phase 2 -↑↑↓, phase 3 -↑↑→, and the high-field phase 4 -↑. It means that 2 3 of the spins in the phases 2 and 3 are parallel to one of the easy axes whereas the remaining 1 3 is antiparallel and perpendicular, respectively, to the same axis. Note that all metamagnetic phases are stoichiometric in the meaning that the concentrations of spins parallel, antiparallel, or perpendicular to the reference axis are rational numbers. The phase diagram of HoNi2B2C at zero temperature is especially simple if the components of magnetic field Hx, Hy are chosen as variables. The experimental phase diagram of HoNi2B2C is shown in Fig. 1 (in the original work [2] it has been presented in polar coordinates h, θ h ).Siegrist et al.[9] and Huang et al.[6] determined the structure of Lu and Ho 1:2:2:1 compounds as the body-centered tetragonal lattice with the space group I4/mmm. The xray structure analysis and the neutron-scattering experiments performed by Goldman et al. [3,4] and Grigereit et al. [5][6][7]. showed that an incommensurate modulated magnetic structures with the wave-vectors Kc = 0.915c * and Ka = 0.585a * occur in the temperature range 4.7-6 K. At temperatures below 4.7 K they vanish and an antiferromagnetic reflections corresponding to alternating ferromagnetic ab-planes of Ho 3+ localizad moments appear. Though the spacial arrangement of the phases ↑↑↓ and ↑↑→ can not bee directly derived from the magnetization measurements, it is unplausible that the ferromagnetic in-plane interaction changes suddenly by switching on of the magnetic field. Therefore, we believe that our symbols ↑↑↓ and ↑↑→ correspond to the real spatial sequences of in-plane magnetic moments. In this article we present a simple microscopic model for magnetic subsystem in the 1:2:2:1 compound which expl...

Field-induced magnetic phase transitions and correlated electronic states in the hexagonal RAgGE and RPtIn series

“…Kalatsky and Pokrovsky (Kalatsky, 1998) elaborated the four-position clock model, which agrees well with the observed metarnagnetism in HoNiZBzC and DyAgSb2.…”

“…6.15 helps in understanding how the hexagonal crystal structure of this compound is reflected in the angular dependence of the metamagnetic phase transitions: similar to the polar phase diagrams for tetragonal compounds HoNizB2C (Kalatsky, 1998) (Myers, 1999a), the equations of these straight lines in polar coordinates c a n be used to verify the transitions already discussed: if we substitute the above slope values in the general formula For the most p a t , the experimental points fall onto the calculated straight lines, as expected. Some deviations from the straight lines can be noticed, with the most evident one for Hc1,2, for which we already emphasized the necessity of a more complex model.…”

“…The present work was initially motivated by the desire to continue the study of complex metarnagnetism in relation to the crystal structure of various compounds; this study already included tetragonal compounds like HoNizBzC (Canfield 1997b;Kalatsky 1998) and DyAgSb2 (Myers 1999), in which the rare earths occupy unique tetragonal positions. We intended to find hexagonal systems suited for such a study, with complex metamagnetic properties, and the search for extremely anisotropic hexagonal compounds turned into a rewarding exploration.…”

“…The anisotropy and metamagnetism are particularly interesting in light of the crystal structure of these compounds, a hexagonal unit cell with unique rare earth site in orthorhombic point symmetry. The four position clock modeE (Kalatsky 1998) …”

Thermodynamic and transport properties of RAgGe (R=Tb–Lu) single crystals

“…The complexity of the M sat (θ)) and H c (θ) phase diagrams drastically increases for systems where the magnetic moments are confined to the abplane, as shown by the detailed analysis of M(H, θ) data done for HoNi 2 B 2 C [3] and DyAgSb 2 [7]. Furthermore, a theoretical model has been developed by Kalatsky and Pokrovsky [8], to explain the experimentally observed behavior of metamagnetism in HoNi 2 B 2 C. An appropriate variant of this four-position clock model subsequently agreed with the data on DyAgSb 2 [7].…”