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Unveiling the magnetic ground states in the iridate double perovskite Pr(2-x)SrxMgIrO6 (x = 0 and 0.5) series

Abhisek Bandyopadhyay, Debu Das, Dheeraj Kumar Pandey, C. Ritter, D. T. Adroja, Sugata Ray

Abstract

We report here the results of a detailed magnetic, thermodynamic, and neutron powder diffraction (NPD) studies carried out on the double perovskite iridates Pr(2-x)SrxMgIrO6 (x = 0 and 0.5). Temperature dependent bulk DC susceptibility data clearly reveals a sharp antiferromagnetic (AFM) transition at 14.5 K in Pr2MgIrO6(x = 0). Next, a weaker signature of an AFM transition at a lower temperature (6 K) is observed in x = 0.5 i.e., Pr1.5Sr0.5MgIrO6 (PSMIO1505). The observed magnetic transitions are further corroborated by the presence of anomalies around the same temperatures in our T-dependent specific heat results. The charge states of both Pr and Ir cations have been confirmed to be the expected ones (3+ for Pr in both the compounds, while Ir is in a pure 4+ state for x = 0 and in a mixed 4+/5+ state for x = 0.5) from the core-level x-ray photoemission spectroscopy (XPS) measurements. Using neutron powder diffraction (NPD) the magnetic ground states and the magnetic moment values were determined for both compounds. Both the Pr- and Ir-sites undergo AFM ordering below the respective transition temperatures, designated by the propagation vector k = ( 1/2 , 0, 1/2 ), in both the compounds.

Unveiling the magnetic ground states in the iridate double perovskite Pr(2-x)SrxMgIrO6 (x = 0 and 0.5) series

Abstract

We report here the results of a detailed magnetic, thermodynamic, and neutron powder diffraction (NPD) studies carried out on the double perovskite iridates Pr(2-x)SrxMgIrO6 (x = 0 and 0.5). Temperature dependent bulk DC susceptibility data clearly reveals a sharp antiferromagnetic (AFM) transition at 14.5 K in Pr2MgIrO6(x = 0). Next, a weaker signature of an AFM transition at a lower temperature (6 K) is observed in x = 0.5 i.e., Pr1.5Sr0.5MgIrO6 (PSMIO1505). The observed magnetic transitions are further corroborated by the presence of anomalies around the same temperatures in our T-dependent specific heat results. The charge states of both Pr and Ir cations have been confirmed to be the expected ones (3+ for Pr in both the compounds, while Ir is in a pure 4+ state for x = 0 and in a mixed 4+/5+ state for x = 0.5) from the core-level x-ray photoemission spectroscopy (XPS) measurements. Using neutron powder diffraction (NPD) the magnetic ground states and the magnetic moment values were determined for both compounds. Both the Pr- and Ir-sites undergo AFM ordering below the respective transition temperatures, designated by the propagation vector k = ( 1/2 , 0, 1/2 ), in both the compounds.
Paper Structure (11 sections, 6 figures, 3 tables)

This paper contains 11 sections, 6 figures, 3 tables.

Table of Contents

  1. Introduction:
  2. EXPERIMENTAL SECTION:
  3. RESULTS AND DISCUSSION:
  4. Structural characterizations by x-ray and neutron powder diffractions
  5. Core-level X-ray photoemission spectroscopy (XPS)
  6. DC magnetic susceptibility and DC magnetization
  7. Heat capacity ($C_p$)
  8. Magnetic Entropy
  9. Neutron powder diffraction (NPD)
  10. CONCLUSIONS
  11. ACKNOWLEDGMENTS

Figures (6)

  • Figure 1: Rietveld refined NPD of (a) Pr$_2$MgIrO$_6$ and (b) Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$. Open black circles represent the experimental data and the continuous red line represents the calculated pattern. The blue line represents the difference between the observed and calculated patterns while the vertical green tick marks indicate the positions of the Bragg reflections of the compounds in $P$2$_{1/n}$ (upper row) and of the vanadium sample holder (lower row). (c) show the crystal structure of Pr$_2$MgIrO$_6$. The rotational distortions (change in O-Ir-O bond angles) within the IrO$_6$ octahedral unit for Pr$_2$MgIrO$_6$ (d), and Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$ (e) samples. In addition, the extent of the geometric frustration within Ir-triangular units is shown for the Pr$_2$MgIrO$_6$ (f), and Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$ (g) compounds.
  • Figure 2: Ir 4$f$ core level XPS spectra (shaded black circles) along with the fitting (red solid line) for (a) Pr$_{2}$MgIrO$_6$ and (b) Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$ samples. Pr 3$d_{5/2}$ core level XPS spectra (shaded black circles) along with the respective fittings (red solid line) for the (c) Pr$_{2}$MgIrO$_6$ and (d) Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$ samples.
  • Figure 3: Zero-field-cooled (open black circles) and field-cooled (crossed blue circles) DC magnetic susceptibilities as a function of temperature for (a) Pr$_2$MgIrO$_6$ and (c) Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$; Inset of (a) reveals the ZFC DC susceptibility curves at various applied magnetic fields, pointing to a field-induced change in the nature of the magnetic transition. Isothermal magnetization ($M-H$) curves at different temperatures for (b) Pr$_2$MgIrO$_6$ and (d) Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$.
  • Figure 4: Specific heat of (a) Pr$_2$MgIrO$_6$ and (b) Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$ at different applied magnetic field (Inset: Magnetic contribution to the specific heat from Debye-Einstein fitting). (c) and (d) depict the corresponding entropy change in Pr$_2$MgIrO$_6$ and Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$ respectively.
  • Figure 5: Low angle part of the thermodiffractogram of Pr$_2$MgIrO$_6$ showing the appearance of magnetic Bragg peaks indexed with $k$ = ($\frac{1}{2}$, 0, $\frac{1}{2}$). The scale of the color-coded intensity contour map is given at the right for reference.
  • ...and 1 more figures