Bhumireddi Sattibabu

Large magnetocaloric effect in hexagonal Yb1−xHoxMnO3

Magnetocaloric properties of polycrystalline hexagonal Yb1−xHoxMnO3 (x = 0.1, 0.2, and 0.3) compounds are studied through magnetization measurements. Temperature dependence of Zero Field Cooled magnetic moment measurements shows Neel temperature (TN1) of ∼83 K, corresponding to the Mn3+ antiferromagnetic ordering. At low temperatures (TN2 ∼ 5 K), all compounds show ferromagnetic ordering due to alignment of the Yb moments and the field induced magnetic transition is observed in the isothermal magnetization measurements. The maximum entropy change |ΔSMmax| and the relative cooling power (RCP) of Yb1−xHoxMnO3 are 3.75 ± 0.78 J/(mol K) and 90.0 ± 27 J/mol for x = 0.3 at ΔH = 100 kOe. Values of both |ΔSMmax| and RCP found to increase with increasing Ho content.

Studies on the magnetoelastic and magnetocaloric properties of Yb1−xMgxMnO3 using neutron diffraction and magnetization measurements

We report the magnetic ordering and magnetoelastic coupling of polycrystalline hexagonal Yb1−xMgxMnO3 (x = 0.00 and 0.05) compounds by using neutron diffraction measurements. The magnetocaloric properties of these Yb1−xMgxMnO3 compounds are also studied using magnetization measurements. The temperature dependence of the lattice parameters (a and c/a ratio) and unit cell volume V show anomalous behavior near TN1 ∼ 85 K (the Mn ordering temperature) due to the magnetoelastic effect. Also all the Mn–O bond distances display considerable variation at TN1. Isothermal magnetization curves measured near the Yb long range ordering temperatures indicate a field induced magnetic transition with applied field. The isothermal magnetic entropy change (−ΔSM) is calculated from the magnetization curves measured for different temperatures. Values of maximum entropy change (−ΔSmaxM), the adiabatic temperature change (ΔTad) and the relative cooling power (RCP) for these compounds are found to be 3.02 ± 0.37 J mol−1 K−1, 8.6 ± 0.95 K and 41 ± 9 J mol−1 for x = 0.00, and 2.63 ± 0.36 J mol−1 K−1, 9.06 ± 0.96 K and 40.0 ± 10 J mol−1 for x = 0.05, respectively, for ΔH = 100 kOe. Rescaling of the −ΔSM vs. T curves for various fields fit into a single curve, implying the second-order phase transition.

Structural, magnetic and magnetocaloric properties of hexagonal multiferroic Yb1−xScxMnO3 (x = 0.1 and 0.2)

We have studied the effect of Sc doping on the structural, magnetic and magnetocaloric properties of multiferroic Yb1−xScxMnO3 (x = 0.1 and 0.2). X-ray powder diffraction shows that both samples crystallize in the hexagonal phase with P63cm space group. The structural analysis shows a decrease in the lattice parameter a, a decrease in the cell volume of the hexagonal unit cell and a decrease in the average bond length between Mn–O, with Sc substitution. Magnetic measurements show that the Neel temperature (TN) increases from 90 K for x = 0.1 to 94 K for x = 0.2 samples. Isothermal magnetic curves show that the field variation in magnetization generates a metamagnetic transition. The maximum entropy change −ΔSmaxM and the relative cooling power (RCP) of Yb1−xScxMnO3 are found to be 2.46 ± 0.40 J mol−1 K−1 and 38.5 ± 9 J mol−1 for x = 0.1 and 1.87 ± 0.31 J mol−1 K−1 and, 30.1 ± 8 J mol−1 for x = 0.2 with ΔH = 10 T. The rescaled magnetic entropy change curves for different applied fields collapse onto a single curve for materials with second-order phase transitions.

Raman spectra and structural properties of hexagonal Yb1-xDyxMnO3 (x = 0, 0.05 and 0.1)

Single phase Yb1-xDyxMnO3 (x= 0, 0.05 and 0.1) samples are prepared by a solid state reaction method. X-ray powder diffraction shows that all samples crystallize in the hexagonal phase with P63cm space group. The structural analysis shows there is increase in lattice parameter c and cell volume of the hexagonal unit cell with Dy substitution and the average bond length between Mn-O increases. Raman spectra show that the phonon peaks of Yb1-xDyxMnO3 slightly shift to lower frequencies with doping.

Effects of Er doping on Raman spectra and on the structural properties of YbMnO3

Polycrystalline samples of Yb1-xErxMnO3 (x= 0, 0.1 and 0.2) were prepared by a solid state reaction procedure. Detailed crystal structure studies were performed using X-ray diffraction data obtained at room temperature. The application of the Rietveld method confirmed the reported hexagonal P63cm phase. Crystallographic parameters for the pure compounds are in agreement with those found in the literature. Changes in the lattice parameters, unit-cell volume, and polyhedral distortions observed in the compounds are explained as a function of x. Raman spectra show that the phonon peaks of Yb1-xErxMnO3 slightly shift to lower frequencies with doping.

Low temperature magnetic properties of magnesium substituted YbMnO3

Structural and magnetic properties of polycrystalline Yb1−xMgxMnO3 (x = 0, 0.05 and 0.10) hexagonal compounds prepared by solid state method, have been studied. The structural analyses of the samples were carried out by Rietveld analysis of neutron diffraction data. With increasing Mg content, we find that the lattice parameter a decreases and c increases whereas the overall Mn-O bond length decreases. Magnetization measured as a function of magnetic field at 2.5 K exhibits hysteresis, which is attributed to ferromagnetic like ordering of Yb3+ sublattice. Temperature dependence of ac magnetic susceptibility, χac(T), shows no signature of spin-glass behavior. χ”(T) exhibits a sudden increase at low temperatures which is due to ordering of Yb3+ sublattice.