Structure and magnetic properties of $Ln\mathrm{MnSbO}$ ($Ln=\mathrm{La}$ and Ce)

Structure and magnetic properties of $L n MnSbO$ ( $L n = La$ and Ce)

Qiang Zhang, C. M. N. Kumar, Wei Tian, Kevin W. Dennis, Alan I. Goldman, and David Vaknin

Phys. Rev. B 93, 094413 – Published 11 March 2016

Abstract

A neutron powder diffraction (NPD) study of $Ln MnSbO$ ( $L n = La$ or Ce) reveals differences between the magnetic ground state of the two compounds due to the strong Ce-Mn coupling compared to La-Mn. The two compounds adopt the P4/nmm space group down to 2 K, and whereas magnetization measurements do not show obvious anomaly at high temperatures, NPD reveals a C-type antiferromagnetic (AFM) order below $T_{N} = 255 K$ for LaMnSbO and 240 K for CeMnSbO. While the magnetic structure of LaMnSbO is preserved to base temperature, a sharp transition at $T_{SR} = 4.5 K$ is observed in CeMnSbO due to a spin-reorientation (SR) transition of the ${Mn}^{2 +}$ magnetic moments from pointing along the $c$ axis to the $a b$ plane. The SR transition in CeMnSbO is accompanied by a simultaneous long-range AFM ordering of the Ce moments, which indicates that the Mn SR transition is driven by the Ce-Mn coupling. The ordered moments are found to be somewhat smaller than those expected for ${Mn}^{2 +}$ ( $S = 5 / 2$ ) in insulators, but large enough to suggest that these compounds belong to the class of local-moment antiferromagnets. The lower $T_{N}$ found in these two compounds compared to the As-based counterparts ( $T_{N} = 317$ for LaMnAsO, $T_{N} = 347 K$ for CeMnAsO) indicates that the Mn- $P n$ ( $P n = As$ or Sb) hybridization that mediates the superexchange Mn- $P n$ -Mn coupling is weaker for the Sb-based compounds.

Received 14 December 2015

DOI:https://doi.org/10.1103/PhysRevB.93.094413

Physics Subject Headings (PhySH)

Antiferromagnetism

Neutron diffraction

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Qiang Zhang^1,2,*, C. M. N. Kumar^3,4, Wei Tian⁵, Kevin W. Dennis¹, Alan I. Goldman^1,2, and David Vaknin^1,2,†

¹Ames Laboratory, Ames, Iowa 50011, USA
²Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
³Jülich Centre for Neutron Science (JCNS), Forschungszentrum Jülich GmbH, Outstation at SNS, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
⁴Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
⁵Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

^*qzhangemail@gmail.com
^†vaknin@ameslab.gov

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Vol. 93, Iss. 9 — 1 March 2016

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Figure 1
Neutron diffraction patterns measured on HB1A (a) at 272 K for LaMnSbO and (b) at 650 K for CeMnSbO. The insets show the corresponding graphic representation of the crystal structure. The blue spheres indicate (a) La and (b) Ce atoms. The observed data and the Rietveld fit are indicated by the open circles and solid lines, respectively, with the difference curve at the bottom. The vertical bars mark the positions of Bragg reflections for the expected “ZrCuSiAs”-type structure (top), and the Al sample holder and impurity phase of Sb in LaMnSbO and MnSb in CeMnSbO (bottom).
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Figure 2
Temperature dependence of the magnetization of LaMnSbO and CeMnSbO at applied magnetic of 0.01 T. The two lowest curves (dashed and solid lines) show the derivatives of the magnetization for both samples with respect to temperature. Note that both curves do not show anomalies at the AFM transition of Mn at around 250 K; however, a sharp peak associated with the Mn spin reorientation and Ce ordering is observed at $T_{SR} = T_{CE} \approx 4.5 K$ .
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Figure 3
(a) Low-angle neutron diffraction scans showing the emergence of the (100) and the increase in intensity (101) reflections for (a) LaMnSbO and (b) CeMnSbO due to a simple Mn AFM ordering (checkerboardlike) as shown in the left part of (c). For CeMnSbO, as the temperature is lowered further (below $\approx 4.5 K$ ), the (100) Bragg reflection is significantly reduced in intensity and simultaneously the (200) gains intensity, indicating a uniform spin flop of the Mn moments from pointing along the $c$ axis to pointing in the $a b$ plane and the emergence of Ce ordering with a magnetic structure, as depicted in the right side of (c).
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Figure 4
Integrated intensities vs temperature of the (100) and (101) Bragg peaks for (a) CeMnSbO and (b) LaMnSbO with a fit to a power law (solid lines). At low temperatures, the (100) peak of CeMnSbO shows a strong reduction in intensity around $T_{SR} = 4.5 K$ .
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Figure 5
Observed (measured on POWGEN) and calculated diffraction patterns and their difference for (a) CeMnAsO and (b) CeMnSbO at 300 K. The left and right frames correspond to the data collected with center wavelengths 1.333 and 3.731 Å, respectively. Note that at 300 K, CeMnAsO is AFM showing extra reflections that are also accounted for in the calculations. The inset in (b) shows the high quality of the POWGEN data and the calculated fit at the high-order reflections region.
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Figure 6
(a) Temperature dependence of cell volumes for CeMnSbO and CeMnAsO. (b) The $c / a$ ratio of cell parameters showing the magnetoelastic effect at the Ce ordering, $T_{Ce} \approx 4.5 K$ for CeMnSbO and $\approx 35 K$ for CeMnAsO. Dotted lines are guides to the eye.
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Physical Review B

covering condensed matter and materials physics

Structure and magnetic properties of $L n MnSbO$ ( $L n = La$ and Ce)

Qiang Zhang, C. M. N. Kumar, Wei Tian, Kevin W. Dennis, Alan I. Goldman, and David Vaknin

Phys. Rev. B 93, 094413 – Published 11 March 2016

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Physical Review B

covering condensed matter and materials physics

Structure and magnetic properties of LnMnSbO (Ln=La and Ce)

Qiang Zhang, C. M. N. Kumar, Wei Tian, Kevin W. Dennis, Alan I. Goldman, and David Vaknin

Phys. Rev. B 93, 094413 – Published 11 March 2016

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Structure and magnetic properties of $L n MnSbO$ ( $L n = La$ and Ce)