Magnetoelastic effects in rare-earth vanadates YbVO 4 and HoVO 4
- PDF / 284,413 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 11 Downloads / 171 Views
SORDER, AND PHASE TRANSITIONS IN CONDENSED SYSTEMS
Magnetoelastic Effects in Rare-Earth Vanadates YbVO4 and HoVO4 Z. A. Kazei and R. I. Chanieva Moscow State University, Vorob’evy gory, Moscow, 119992 Russia e-mail: [email protected] Received August 11, 2005
Abstract—Magnetoelastic anomalies in the thermal expansion and Young modulus, as well as the ∆E-effect in rare-earth vanadates RVO4 (R = Ho, Yb), are investigated experimentally and theoretically. A considerable softening of the Young modulus is observed for HoVO4 and YbVO4 at T < 70 K and T < 150 K, respectively; this effect is adequately described in the framework of the generalized susceptibility formalism. It is shown that the field dependences of the ∆E-effect and their temperature variation in YbVO4 can also be described using this approach. To compare with experiment, the magnetoelastic contributions to the Young modulus of an isotropic polycrystal from various elastic modes have been averaged. For the Yb vanadate, considerable magnetoelastic anomalies in the thermal expansion along the tetragonal a and c axes have been discovered. The magnetoelastic contributions are used for determining completely symmetric magnetoelastic coefficients; the role of the completely symmetric quadrupole constant for magnetoelastic effects is analyzed. PACS numbers: 71.70.–d, 75.30.Cr, 75.30.Sg DOI: 10.1134/S1063776106020087
1. INTRODUCTION Complex studies of rare-earth (RE) compounds clarify the nature of fundamental interactions determining their magnetic behavior, viz., crystal field, magnetoelastic (ME), bilinear, and quadrupole (Jahn–Teller) interactions. The ME interaction in RE compounds, which is responsible for various ME effects, plays an important role in the formation of their magnetic characteristics. The analysis of this interaction is one of the current problems in solid-state physics. Analysis of ME contributions to various magnetic characteristics provides important information on the nature of the ME interaction and makes it possible to determine the ME coefficients of various symmetry. The ME interaction in RE compounds is studied using various experimental methods, such as the measurement of temperature dependences of crystal lattice parameters, magnetostriction, elastic constants, and the ∆E-effect. Here, we report on experimental investigation of anomalies in thermal expansion, Young modulus, and the ∆E-effect in RE vanadates RVO4 (R = Ho, Yb) with zircon structure. Such anomalies were studied earlier for other compounds of this family [1–3] (mainly, with a strong Jahn–Teller (JT) interaction). Although the JT interactions in Yb and Ho vanadates do not lead to spontaneous structural transitions, we believe that such interactions may result in the observable ME effects. Earlier experiments with Yb vanadate and phosphate made it possible to determine the constants of
microscopic interactions [4–6] and proved that their magnetic properties are qualitatively similar. According to Mössbauer studies, the magnetic ordering in YbVO4 and YbPO4 appears at
Data Loading...
