Speaker
Description
GdMnO3 came to the attention of the scientists due to the discovery of multiferroicity in this compound. It crystallizes in the orthorhombically distorted perovskite structure; space group 𝑃𝑛𝑚𝑎; Gd ions are located on 4𝑐; Mn ions on 4𝑏 and oxygen anions are located on 4𝑐 and 8𝑑 crystallographic sites. The compound orders into antiferromagnetic phase below 𝑇N ~ 40 K [1] and then undergoes order-to-order magnetic phase transition into low temperature canted magnetic phase at 𝑇lock (~ 20 K). GdMn1-xTixO3 (0 ≤ x ≤ 0.1) compounds were synthesized by the floating zone method to understand the role of Ti substitution on structural, magnetic, and magnetocaloric properties. Raman spectroscopy and X-ray diffraction, along with Rietveld refinement, confirm the pure phase of all compositions having an orthorhombic perovskite structure (space group; Pnma). The Neel temperature TN is not visible on magnetization measurements; however, from the combination of zero-field-cooled; field-cooled magnetization data and hysteresis loops M(B), we concluded the decrease of TN from 42 K (x = 0) to roughly 30 K (x = 0.1). Tlock has been also shifted from ~20 K (x = 0) to ~2 K (x = 0.1). In the temperature interval Tlock < T < TN the M(B) curves show simple antiferromagnetic behavior, however, below Tlock the character of M(B) curves changed from complicated butterfly-type (x = 0) to simple ferromagnetic one (x = 0.1). This suggests that Ti destabilizes the magnetic structure or at least prevents the Gd sublattice from ordering. Magnetic entropy change (ΔSM) is extremely sensitive to the direction of the applied field and can be negative (normal MCE) or positive (inverse MCE). The Gd ordering induces an inverse MC effect along ‘c’ and ‘b’ axes, whereas it’s not seen along the ‘a’ axis, revealing complex anisotropic magnetic ordering. The magnetic entropy change displays a broad peak at T1 ~ 13 K with -ΔSM = 11.35, 8.05, and 7.77 J/kg-K and corresponding relative cooling power (RCP) = 197.72, 164.70, and 166.78 J/kg for x = 0.0, 0.05, and 0.1, respectively, under 5 T. A sharp -ΔSM = 0.55 J/kg-K (0.5 T) appears at Tlock = 20 K (x = 0.0), which is shifted to higher temperatures with a magnetic field. The large cryogenic MCE suggests these compounds are promising for low-temperature magnetic refrigeration applications.
Acknowledgements
This publication is the result of the project implementation: VEGA 2/0004/25.
References
[1] N. Pavan Kumar et al., Phys. Scr., Vol. 83, p.045701 (2011)
