Low-temperature properties of Ca-doped YbMnO3 multiferroic single crystals

Abstract

The specific heat cp and magnetization of single crystal hexagonal manganites of the type Yb1−xCaxMnO3 (x = 0, 0.05, and 0.10) were measured in a wide temperature range as a function of magnetic field. Antiferromagnetic ordering of the Mn sublattice occurs at TN = 83 K. Ca doping has surprisingly minimal effect on the magnetic properties. At low temperature (∼3.5 K), all compounds show ferromagnetic (FM) ordering in the basal plane attributed to Yb in site 2a. For low fields applied along the c direction, Yb spin reorientation occurs and FM ordering disappears. cp shows a broad maximum centered at the temperature ∼6 K that is consistent with a Schottky anomaly related to the Zeeman splitting of the Yb moments due to Mn molecular field. In the field of 30 kOe, the re-entrant FM transition takes place with Yb ions in sites 2a and 4b.

Thermodynamic properties of multiferroic Mg doped YbMnO3

“…The larger molecular field for x = 0.05 sample results in higher T N as observed. These molecular field and Schottky gap values are nearly the same as reported values in literature[10,11].C mag /T vs. T curves for YbMnO 3 and Yb 0.95 Mg 0.05 MnO 3 are shown in…”

“…Just above T c , a broad hump is observed for both samples which are speculated to be Schottky anomalies [10] due to Yb in site 4b in the Mn molecular field as shown in Fig. 5b.…”

“…The Schottky anomaly for these samples is due to the Zeeman like splitting of crystal fields in ground state multiplet of the Yb 3+ ions [10,11]. Assuming that the effective moment of Yb 3+ ions in the ground state is l Yb and that the splitting of the doublet is D Sch = 2l Yb H mf, contribution from a two level Schottky function should fit the specific heat data at low temperatures (T < 15 K).…”

“…They reported that the magnetic transition temperature increased from 82 K to 95 K and the ferroelectric loop became more lossy with increasing iron (Fe) content. Abramov et al [10] have reported two peaks in heat capacity measurements of Ca doped YbMnO 3 at low temperatures, one sharp at the transition temperature and one broad at slightly higher temperature. The sharp peak is attributed to the ferromagnetic (FM) ordering in the basal plane due to Yb in site 2a and the broad peak, centered at 6 K, is consistent with the Schottky anomaly related to the Zeeman splitting of the Yb moments due to the Mn molecular field.…”

Magnetocaloric effect in hexagonal Yb0.9Mg0.1MnO3

“…A Schottky anomaly is also observed at $ 6.7 K due to Yb 3 þ ions in site 4b in the Mn molecular field [8]. The value of the energy splitting due to the molecular field of Mn is given by Δ sch ¼2m Yb H mf , where m Yb is the moment of Yb in the site 4b, and H mf is the effective molecular field at Yb 4b sites.…”