Exchange bias and spin glass states driven by antisite disorder in the double perovskite compound ${\mathrm{LaSrCoFeO}}_{6}$

Exchange bias and spin glass states driven by antisite disorder in the double perovskite compound ${LaSrCoFeO}_{6}$

R. C. Sahoo, Y. Takeuchi, A. Ohtomo, and Z. Hossain

Phys. Rev. B 100, 214436 – Published 26 December 2019

Abstract

Antisite (B-site) disorder in double perovskite lattice is responsible for various magnetic phenomena such as exchange bias, spin glass, memory effect, colossal magnetoresistance, etc. By controlling the antisite disorder in the antiferromagnetic double perovskite ${LaSrCoFeO}_{6}$ , we achieve intrinsic exchange bias effect with a large exchange bias field ( $\sim 1.2$ kOe) and giant coercive field ( $\sim 12.8$ kOe). Further, we find that the effect of such antisite disorder induces a spin-glass state in ${LaSrCoFeO}_{6}$ . Multiple signatures of slow dynamics were confirmed by frequency-dependent peak shift, slow spin relaxation, and memory effect over a wide temperature regime ( $5 - 80$ K). The AC susceptibility data near the spin-glass temperature ( $\sim 72.1 \pm 0.6$ K) are best fit by a critical slowing down model described by a dynamical exponent $z ν = 7.5 \pm 0.5$ and $τ_{0} = 1.05 \times 10^{- 12}$ s. The origin of exchange bias and spin glass are briefly discussed.

Received 21 August 2019
Revised 3 December 2019

DOI:https://doi.org/10.1103/PhysRevB.100.214436

Physics Subject Headings (PhySH)

Antiferromagnetism Exchange bias Ferromagnetism Magnetic anisotropy Magnetic susceptibility Magnetism Spin dynamics Spin relaxation

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

R. C. Sahoo^1,*, Y. Takeuchi², A. Ohtomo^2,3, and Z. Hossain^1,†

¹Department of Physics, Indian Institute of Technology, Kanpur 208016, India
²Department of Chemical Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan
³Materials Research Center for Element Strategy (MCES), Tokyo Institute of Technology, Yokohama 226−8503, Japan

^*rsahoo@iitk.ac.in
^†zakir@iitk.ac.in

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Vol. 100, Iss. 21 — 1 December 2019

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Figure 1
Room-temperature powder x-ray diffraction pattern of LSCFO sample (dots) with the fitted curve (red line) and the difference (blue line), using Rietveld refinement. Inset shows a polyhedral picture of the unit cell of monoclinic LSCFO, where big balls (blue) and small balls (red) represent La/Sr and O atoms, respectively, while pink and yellow octahedra denote ${CoO}_{6}$ and ${FeO}_{6}$ , respectively.
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Figure 2
(a) ZFC $M (H)$ isotherms in the range $\pm 60$ kOe at 5 K and 300 K. Inset shows the “virgin” $M (H)$ isotherm (black dots) taken from 5 K and the theoretical fit (red line) of Eq. (1) with $M_{S} = 2.9 μ_{B}$ /f.u., $a = 11393.4$ Oe, $b = 4.03 \times 10^{7}$ ( ${Oe)}^{2}$ , and $c = 2.55 \times 10^{- 6} μ_{B}$ /(f.u.-Oe) in the field range of 20 $kOe \leq$ H $\leq 60$ kOe. (b) Two-dimensional schematic crystal-structure model for ASD LSCFO system. In this model, the atomic interchange between Co-Fe pair and degrees of antisite disorder are indicated. (c) The $M (H)$ isotherms measured at 5 K after cooling the sample from 300 K under $+ 30$ kOe (black curve) and $- 30$ kOe (red curve) fields using two different protocols: (1) $H_{CF} = + 30$ kOe: $+ 30$ kOe $\to + 60$ kOe $\to - 60$ kOe $\to + 60$ kOe and (2) $H_{CF} = - 30$ kOe: $- 30$ kOe $\to - 60$ kOe $\to + 60$ kOe $\to - 60$ kOe. (d) $M (H)$ isotherms in ZFC and FC modes at different cooling fields of 0, 30, and 60 kOe. (e) Cooling field dependent $H_{EB}$ and $H_{C}$ change at 5 K. (f) The variation of $M_{E B}$ and $M_{C}$ as a function of cooling fields.
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Figure 3
(a) The zoomed view of the $M (H)$ isotherms in negative field axis measured at 5 K after $+ 30$ kOe cooling field, with ten continuous loops (magnetic training effect of EB). (b) The number of field cycle ( $λ$ ) dependence of $H_{EB}$ extracted from training effect at 5 K. The connecting lines are the best fitted by two different models mentioned in the text.
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Figure 4
(a) $M (T)$ curve of LSCFO measured at 500 Oe DC magnetic field $H_{DC}$ under ZFC and FC mode and its temperature derivative $d M_{ZFC} / d T$ as a function of temperature. (b) The DC $M (T)$ curves measured under various $H_{DC}$ fields of 50, 100, 500, and 1000 Oe. Inset shows the corresponding plot of $H_{DC}^{2 / 3}$ versus $T_{irr}$ obtained from $M (T)$ curves and a linear fitting by De Almeida-Thouless (AT) line.
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Figure 5
Temperature-dependent real $χ^{'}$ (T) at different frequencies of 3, 50, 150, and 350 Hz. Inset shows relaxation time ( $τ$ ) versus $T_{f}$ at various $f$ and the solid line (red) denotes a best fit to the critical slowing down model given in Eq. (5).
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Figure 6
(a) Raw data of magnetic field and temperature as a function of time ( $t$ ) varied during memory effect experiments. (b) Temperature-dependent FC magnetization data recorded during the memory effect experiments. Inset shows zoomed view of FC magnetization versus temperature curves at high temperature regime. (c) and inset in (c) show the extended view of FC magnetization versus temperature curve in the low temperature regime. (d) Time dependence of isothermal (at 45 K) magnetization measured in the FC mode with an applied DC field of 100 Oe for different waiting times ( $t_{W}$ ) of $10^{2}$ , $10^{3}$ , and $10^{4}$ sec; the corresponding solid lines (red) are the best fit using the stretched exponential function described in Eq. (6).
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Physical Review B

covering condensed matter and materials physics

Exchange bias and spin glass states driven by antisite disorder in the double perovskite compound ${LaSrCoFeO}_{6}$

R. C. Sahoo, Y. Takeuchi, A. Ohtomo, and Z. Hossain

Phys. Rev. B 100, 214436 – Published 26 December 2019

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Physical Review B

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Exchange bias and spin glass states driven by antisite disorder in the double perovskite compound LaSrCoFeO6

R. C. Sahoo, Y. Takeuchi, A. Ohtomo, and Z. Hossain

Phys. Rev. B 100, 214436 – Published 26 December 2019

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Exchange bias and spin glass states driven by antisite disorder in the double perovskite compound ${LaSrCoFeO}_{6}$