Magnetoelectric and Raman spectroscopic studies of monocrystalline $\mathrm{MnC}{\mathrm{r}}_{2}{\mathrm{O}}_{4}$

Magnetoelectric and Raman spectroscopic studies of monocrystalline $MnC r_{2} O_{4}$

G. T. Lin, Y. Q. Wang, X. Luo, J. Ma, H. L. Zhuang, D. Qian, L. H. Yin, F. C. Chen, J. Yan, R. R. Zhang, S. L. Zhang, W. Tong, W. H. Song, P. Tong, X. B. Zhu, and Y. P. Sun

Phys. Rev. B 97, 064405 – Published 12 February 2018

Abstract

$MnC r_{2} O_{4}$ that exhibits spin frustration and complex spiral spin order is of great interest from both fundamental as well as application-oriented perspectives. Unlike $CoC r_{2} O_{4}$ , whose ground state presents the coexistence of commensurate spiral spin order (CSSO) and ferroelectric order, $MnC r_{2} O_{4}$ shows no multiferroicity. One reason is that the spiral spin order is highly sensitive to the oxygen concentration in $MnC r_{2} O_{4}$ . Here, we have successfully grown high-quality single-crystalline $MnC r_{2} O_{4}$ by the chemical vapor transport method. We observe a first-order magnetic transition from the incommensurate spiral spin order (ICSSO) at 19.4 K to the CSSO at 17.4 K. This magnetic transition is verified by magnetization, specific heat, and magnetoelectric measurements, which also confirm that the ground state exhibits the coexistence of the CSSO and magnetoelectricity below 17.4 K. Interestingly, the temperature evolution of Raman spectra between 5.4 and 300 K suggests that the structure remains the same. We also find that the phase-transition temperature of the CSSO decreases as applied magnetic field increases up to 45 kOe.

Received 15 December 2017

DOI:https://doi.org/10.1103/PhysRevB.97.064405

Physics Subject Headings (PhySH)

Ferrimagnetism Ferroelectricity Magnetic susceptibility Magnetoelectric effect

Multiferroics

Magnetization measurements Specific heat measurements

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

G. T. Lin^1,2, Y. Q. Wang^2,3, X. Luo^1,*, J. Ma^4,5, H. L. Zhuang⁶, D. Qian^5,7, L. H. Yin¹, F. C. Chen^1,2, J. Yan^1,2, R. R. Zhang³, S. L. Zhang³, W. Tong³, W. H. Song¹, P. Tong¹, X. B. Zhu¹, and Y. P. Sun^1,3,7,†

¹Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China
²University of Science and Technology of China, Hefei 230026, China
³High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, China
⁴Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
⁵Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
⁶School for Engineering of Matter, Transport & Energy, Arizona State University, Tempe, Arizona 85287, USA
⁷Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China

^*xluo@issp.ac.cn
^†ypsun@issp.ac.cn

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Vol. 97, Iss. 6 — 1 February 2018

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Figure 1
(a) Temperature-dependent magnetization $M$ ( $T$ ) of $MnC r_{2} O_{4}$ under the ZFC, FCC, and FCW with an applied magnetic field $H$ of 50 Oe, parallel to the ⟨111⟩ direction. The inset (i) shows the temperature-dependent inverse susceptibility $χ {(T)}^{- 1}$ . The red solid line is the fitting result according to Eq. (1). The inset (ii) shows the temperature-dependent magnetization $M$ ( $T$ ) measurements of samples 1 and 2 with $H = 50 Oe$ , parallel to the ⟨111⟩ direction. (b) The isothermal magnetization curves $M$ ( $H$ ) at 5 K, parallel to the ⟨111⟩ direction. The insets (i) and (ii) present the time-dependent magnetization $M$ ( $t$ ) under FCC mode below $T_{C}$ . (c)–(e) The enlarged view of the $M$ ( $T$ ) under FCC and FCW modes with different applied magnetic field, parallel to the (111) plane.
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Figure 2
(a) Specific heat $C_{p}$ as a function of $T$ for $MnC r_{2} O_{4}$ and the fitted $C_{V}^{Debye} (T)$ using Eqs. (3) and (4). (b) Temperature-dependent magnetic specific heat $C_{mag} (T)$ . The inset shows the magnetic entropy $S_{mag} (T)$ . The red dashed line refers to ${S_{mag}}_{} (T \to \infty)$ calculated with the magnetic moment $S = 5 / 2$ for $M n^{2 +}$ and $S = 3 / 2$ for $C r^{3 +}$ . (c) The enlarged view of the $C_{p} (T)$ under cooling and warming modes with $H = 0 Oe$ .
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Figure 3
(a) Temperature-dependent Raman spectra of $MnC r_{2} O_{4}$ ; Temperature-dependent Raman phonon frequencies of (b) $T_{2 g} (1)$ , (c) $T_{2 g} (2)$ , (d) $T_{2 g} (3)$ , and (e) $A_{1 g}$ modes. The red solid lines are the anharmonic contributions to the phonon frequencies fitted by Eq. (7). Temperature-dependent linewidth of (f) $T_{2 g} (2)$ and (g) $A_{1 g}$ modes.
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Figure 4
(a) Temperature-dependent electric polarization $P$ ( $T$ ) and $M$ ( $T$ ) along the [111] direction. (b) $P$ ( $T$ ) along the [111] direction around the $T_{L}$ with different applied field. (c) The $M$ ( $H$ ) at 10 K, parallel to the ⟨111⟩ direction. The field-dependent electric polarization $P$ ( $H$ ) at 10 and 17 K, respectively, parallel to the ⟨111⟩ direction. (d) The synchronous reversal of the spontaneous $M$ and $P$ between +1.5 and −1.5 kOe at 10 K.
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Figure 5
(a) Schematic structure of spinel $MnC r_{2} O_{4}$ . The electron configuration of $M n^{2 +}$ and $C r^{3 +}$ ions, located at the center of tetrahedral and octahedral $O^{2 -}$ cages, respectively. Here, the splitting due to the local crystal field of the ions in the cubic phase and the effect of Hund coupling are only taken into account. (b) Low-temperature magnetic structure of spinel $MnC r_{2} O_{4}$ viewed along $[1 \bar{1} 0]$ direction. (c) The spin ( $S_{i}$ and $S_{j}$ ) canting between the two sites ( $i$ and $j$ ) and the direction of induced polarization $P$ . (d) Schematic low-temperature phase diagram of $MnC r_{2} O_{4}$ . The open circles and triangles refer to the phase-transition temperature obtained by $M$ ( $T$ ) and $P$ ( $T$ ) curves along the [111] directions, respectively.
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Physical Review B

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Magnetoelectric and Raman spectroscopic studies of monocrystalline $MnC r_{2} O_{4}$

G. T. Lin, Y. Q. Wang, X. Luo, J. Ma, H. L. Zhuang, D. Qian, L. H. Yin, F. C. Chen, J. Yan, R. R. Zhang, S. L. Zhang, W. Tong, W. H. Song, P. Tong, X. B. Zhu, and Y. P. Sun

Phys. Rev. B 97, 064405 – Published 12 February 2018

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Physical Review B

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Magnetoelectric and Raman spectroscopic studies of monocrystalline MnCr2O4

G. T. Lin, Y. Q. Wang, X. Luo, J. Ma, H. L. Zhuang, D. Qian, L. H. Yin, F. C. Chen, J. Yan, R. R. Zhang, S. L. Zhang, W. Tong, W. H. Song, P. Tong, X. B. Zhu, and Y. P. Sun

Phys. Rev. B 97, 064405 – Published 12 February 2018

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Magnetoelectric and Raman spectroscopic studies of monocrystalline $MnC r_{2} O_{4}$