Temperature and field dependence of magnetic domains in ${\mathrm{La}}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$

Temperature and field dependence of magnetic domains in ${La}_{1.2} {Sr}_{1.8} {Mn}_{2} O_{7}$

Benjamin Bryant, Y. Moritomo, Y. Tokura, and G. Aeppli

Phys. Rev. B 91, 134408 – Published 8 April 2015

Abstract

Colossal magnetoresistance and field-induced ferromagnetism are well documented in manganite compounds. Since domain wall resistance contributes to magnetoresistance, data on the temperature and magnetic field dependence of the ferromagnetic domain structure are required for a full understanding of the magnetoresistive effect. Here we show, using cryogenic magnetic force microscopy, domain structures for the layered manganite ${La}_{1.2} {Sr}_{1.8} {Mn}_{2} O_{7}$ as a function of temperature and magnetic field. Domain walls are suppressed close to the Curie temperature $T_{C}$ , and appear either via the application of a $c$ -axis magnetic field, or by decreasing the temperature further. At temperatures well below $T_{C}$ , new domain walls, stable at zero field, can be formed by the application of a $c$ -axis field. Magnetic structures are seen also at temperatures above $T_{C}$ : these features are attributed to inclusions of additional Ruddleston-Popper manganite phases. Low-temperature domain walls are nucleated by these ferromagnetic inclusions.

Received 11 December 2014
Revised 11 February 2015

DOI:https://doi.org/10.1103/PhysRevB.91.134408

Authors & Affiliations

Benjamin Bryant^1,*, Y. Moritomo², Y. Tokura^3,4,5, and G. Aeppli^1,6,7,8

¹London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom
²Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
³Multiferroic Project, ERATO, Japan Science and Technology Agency (JST), Wako, 351-0198, Japan
⁴Cross-Correlated Materials Research Group (CMRG), RIKEN, Advanced Science Institute, Wako, 351-0198, Japan
⁵Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
⁶Department of Physics, ETH Zürich, CH-8093 Zürich, Switzerland
⁷Department of Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
⁸Synchrotron and Nanotechnology Department, Paul Scherrer Institute, CH-5232, Villigen, Switzerland

^*Present address: Delft University of Technology, Kavli Institute of Nanoscience, Department of Quantum Nanoscience, Lorentzweg 1, 2628 CJ Delft, The Netherlands, ben.e.bryant@gmail.com

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Vol. 91, Iss. 13 — 1 April 2015

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Figure 1
(a) Crystal structure of ${La}_{1.2} {Sr}_{1.8} {Mn}_{2} O_{7}$ (b) $c$ -axis resistivity as a function of temperature and $c$ -axis field. Also shown is the magnetoresistance $R_{0 T} / R_{6 T}$ . (c) Room temperature AFM topograph. The scale line shows the location of the cross section (d). (e) $25 \times 25$ $μ m$ MFM image collected at 4.7 K, showing domain walls. (f) Corresponding AFM topographic image.
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Figure 2
$26 \times 26$ $μ m$ MFM images at 80 K (a), 95 K (b), and 100 K (c). Domain walls, visible at 80 K, have disappeared at 100 K, leaving only topographic features. (d) AFM topographic image. (e) Comparison of bulk magnetization ( $H = 100$ $Oe ∥ a b$ ) and surface domain wall contrast as observed by MFM, as functions of temperature: the dashed line is a guide to the eye. A steep drop in the visibility of domain walls is seen at 95 K, well below the bulk $T_{C} = 118$ K. The domain wall contrast is quantified as the peak to peak contrast, measured from a section through each MFM ( $Δ f$ ) image. The section position is indicated in (c).
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Figure 3
(a) Field dependence of MFM imaging at 100 K: the area is the same as for Fig. 2. (b) Field dependence of MFM imaging at 118 K: the area is the same as (a). All MFM images are $26 \times 26$ $μ m$ . (c) Domain wall contrast as a function of field for 100 K and 118 K. Dashed lines are guides to the eye. (d) Bulk magnetization vs applied field ( $H ∥ c$ ) for 2 K, 100 K, and 118 K. Neither MFM data nor $M$ vs $H$ have been corrected for the demagnetizing field, though both samples have a similar aspect ratio.
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Figure 4
Field dependence of MFM images at 20 K (a) zero field MFM image, $15 \times 15$ $μ m$ . Some crosstalk with the topographic image is visible. Under 0.6 T applied field (b) a new domain wall (indicated) is formed: this is wiped out by a field of 2.0 T (c). (d) Zero field MFM image, after a field of 8 T was applied. A new domain wall (indicated), stable at zero field, is observed. (e) $M$ vs $H$ for 2 K and 50 K, $H ∥ c$ , showing negligible hysteresis. (f) Topographic image of same area as (a)–(d). All images $15 \times 15$ $μ m$ ; all MFM images have the same color scale of $\pm 0.1$ Hz.
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Figure 5
Magnetic contrast above and below $T_{C}$ (a) $15 \times 15$ $μ m$ MFM image at 260 K (b) same area at 50 K. (c) Topographic image at 260 K of same area as (a) and (b), showing terrace edges, and also some crosstalk from the magnetic image. (d) Same as (b): dashed lines highlight magnetic features which persist above $T_{C}$ .
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Figure 6
(a) $M$ vs $T$ and $d M / d T$ for the temperature range 2 K to 350 K ( $H = 100$ $Oe ∥ a b$ ). In addition to the bulk $T_{C} = 118$ K, magnetic transitions are observed at $T_{1} = 245$ K, $T_{2} = 285$ K, and $T_{3} = 335$ K. (b) $M$ vs $H$ for 2 K, 100 K, and 150 K. The inset shows $M$ vs $H$ at 150 K with the paramagnetic background subtracted: a residual ferromagnetic component is observed.
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Temperature and field dependence of magnetic domains in ${La}_{1.2} {Sr}_{1.8} {Mn}_{2} O_{7}$

Benjamin Bryant, Y. Moritomo, Y. Tokura, and G. Aeppli

Phys. Rev. B 91, 134408 – Published 8 April 2015

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Physical Review B

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Temperature and field dependence of magnetic domains in La1.2Sr1.8Mn2O7

Benjamin Bryant, Y. Moritomo, Y. Tokura, and G. Aeppli

Phys. Rev. B 91, 134408 – Published 8 April 2015

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Temperature and field dependence of magnetic domains in ${La}_{1.2} {Sr}_{1.8} {Mn}_{2} O_{7}$