Helical magnetism in Sr-doped $\mathrm{CaM}{\mathrm{n}}_{7}{\mathrm{O}}_{12}$ films

Helical magnetism in Sr-doped $CaM n_{7} O_{12}$ films

Amanda Huon, Anuradha M. Vibhakar, Alexander J. Grutter, Julie A. Borchers, Steven Disseler, Yaohua Liu, Wei Tian, Fabio Orlandi, Pascal Manuel, Dmitry D. Khalyavin, Yogesh Sharma, Andreas Herklotz, Ho Nyung Lee, Michael R. Fitzsimmons, Roger D. Johnson, and Steven J. May

Phys. Rev. B 98, 224419 – Published 19 December 2018

Abstract

Noncollinear magnetism can play an important role in multiferroic materials but is relatively understudied in oxide heterostructures compared to their bulk counterparts. Using variable temperature magnetometry and neutron diffraction, we demonstrate the presence of helical magnetic ordering in $CaM n_{7} O_{12}$ and $C a_{1 - x} S r_{x} M n_{7} O_{12}$ (for $x$ up to 0.51) thin films. Consistent with bulk $C a_{1 - x} S r_{x} M n_{7} O_{12}$ , the net magnetization increases with Sr doping. Neutron diffraction confirms that the helical magnetic structure remains incommensurate at all values of $x$ , while the fundamental magnetic wavevector increases upon Sr substitution. This result demonstrates a chemical-based approach for tuning helical magnetism in quadruple perovskite films and enables future studies of strain and interfacial effects on helimagnetism in oxide heterostructures.

Received 30 August 2018
Revised 12 November 2018

DOI:https://doi.org/10.1103/PhysRevB.98.224419

Physics Subject Headings (PhySH)

Complex oxides Helimagnets Perovskites

Neutron diffraction

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Amanda Huon¹, Anuradha M. Vibhakar², Alexander J. Grutter³, Julie A. Borchers³, Steven Disseler³, Yaohua Liu⁴, Wei Tian⁴, Fabio Orlandi⁵, Pascal Manuel⁵, Dmitry D. Khalyavin⁵, Yogesh Sharma⁶, Andreas Herklotz⁶, Ho Nyung Lee⁶, Michael R. Fitzsimmons^4,7, Roger D. Johnson², and Steven J. May^1,*

¹Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, USA
²Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, OX1 3PU, United Kingdom
³NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
⁴Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
⁵ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
⁶Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
⁷Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA

^*smay@drexel.edu

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Vol. 98, Iss. 22 — 1 December 2018

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Figure 1
Effect of Sr doping on the crystal structure of $C a_{1 - x} S r_{x} M n_{7} O_{12}$ films synthesized on $SrLaAl O_{4}$ . (a) 2θ–θ x-ray diffraction scans of $C a_{1 - x} S r_{x} M n_{7} O_{12}$ films displaying the $00 l$ reflections of the pseudocubic structure. The $c$ axis expands with increasing Sr doping. The data sets are presented in order of Sr content with the $x = 0$ data on bottom (black line) and the $x = 0.51$ data on top (green line). (b) RSMs show the 103 Bragg reflection of $C a_{1 - x} S r_{x} M n_{7} O_{12}$ films, confirming that the in-plane strain is relaxed. (c) Room temperature Raman spectra of the $C a_{1 - x} S r_{x} M n_{7} O_{12}$ films exhibits nine active modes. The Raman modes of the substrate are indicated by the dotted lines.
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Figure 2
(a) – (d) Normalized reciprocal space maps about the 222 reflection for each of the four rhombohedral domains within the undoped $CaM n_{7} O_{12}$ film. (e) Fitted line scan taken through (d). The raw data is given by the black circles, the total fitted data by the red line, the polynomial background by the green line and the two diffraction peaks by the blue lines.
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Figure 3
(a) Temperature dependence of magnetization measured with $μ_{0} H = 0.1 T$ applied parallel to the film surface of the $C a_{1 - x} S r_{x} M n_{7} O_{12}$ films. Magnetization data in (a) were obtained upon warming after field-cooling in 0.1 T. The vertical dotted lines show the $T_{N 2}$ values reported for bulk $CaM n_{7} O_{12}$ and $SrM n_{7} O_{12}$ in Ref. [25], for comparison. (b) Magnetization as a function of applied field at 10 K.
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Figure 4
Neutron diffraction data along the pseudocubic [111] direction obtained from the $CaM n_{7} O_{12}$ film using the WISH instrument at sample temperatures of 100, 65, and 2 K. The raw data minus the background are given by the red circles and the fitted peaks are given by the solid black line. The magnetic satellite peaks are labeled as in Ref. [18]. The inset of (a) shows a schematic of the scattering vector with respect to the thin film geometry, while $| Q_{k 0} |$ is defined in (b).
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Figure 5
Neutron diffraction temperature maps for (a) $CaM n_{7} O_{12}$ and (b) $C a_{0.78} S r_{0.22} M n_{7} O_{12}$ . Adjacent plots to the right show the intensity as a function of |Q| at individual temperatures. In all plots, the |Q| vector is along the [111] direction. Error bars indicate the square root of the number of counts.
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Figure 6
The length of the $k_{0}$ wavevector as a function of (a) temperature and (b) Sr concentration at the lowest temperatures measured. The two $x = 0$ data points were obtained at 2 K with the WISH diffractometer (open circle) and 6 K with the SPINS instrument (closed circle) from different $CaM n_{7} O_{12}$ samples. The $x = 0.51$ sample was measured at 6 K and the $x = 0.22$ sample was measured at 10 K. Data from bulk $CaM n_{7} O_{12}$ and $SrM n_{7} O_{12}$ measured at 1.5 K is represented by open squares; this data comes from Ref. [25]. Error bars represent ±1 standard deviation.
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Physical Review B

covering condensed matter and materials physics

Helical magnetism in Sr-doped $CaM n_{7} O_{12}$ films

Amanda Huon, Anuradha M. Vibhakar, Alexander J. Grutter, Julie A. Borchers, Steven Disseler, Yaohua Liu, Wei Tian, Fabio Orlandi, Pascal Manuel, Dmitry D. Khalyavin, Yogesh Sharma, Andreas Herklotz, Ho Nyung Lee, Michael R. Fitzsimmons, Roger D. Johnson, and Steven J. May

Phys. Rev. B 98, 224419 – Published 19 December 2018

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Physical Review B

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Helical magnetism in Sr-doped CaMn7O12 films

Amanda Huon, Anuradha M. Vibhakar, Alexander J. Grutter, Julie A. Borchers, Steven Disseler, Yaohua Liu, Wei Tian, Fabio Orlandi, Pascal Manuel, Dmitry D. Khalyavin, Yogesh Sharma, Andreas Herklotz, Ho Nyung Lee, Michael R. Fitzsimmons, Roger D. Johnson, and Steven J. May

Phys. Rev. B 98, 224419 – Published 19 December 2018

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Helical magnetism in Sr-doped $CaM n_{7} O_{12}$ films