Superconductivity under pressure in $R$FeAsO${}_{1\ensuremath{-}x}$F${}_{x}$ ($R$ $=$ La, Ce$\ensuremath{-}$Sm) by dc magnetization measurements

Superconductivity under pressure in $R$ FeAsO $_{1 - x}$ F $_{x}$ ( $R$ $=$ La, Ce $-$ Sm) by dc magnetization measurements

Kiyotaka Miyoshi, Eiko Kojima, Saki Ogawa, Yuta Shimojo, and Jun Takeuchi

Phys. Rev. B 87, 235111 – Published 11 June 2013

Abstract

Superconducting transition under pressure ( $P$ ) has been investigated for optimum-doped $R$ FeAsO $_{1 - x}$ F $_{x}$ ( $R = La$ , Ce–Sm) by dc magnetization measurements. For $R = La$ , $T_{c}$ is found to be pressure independent up to $P \sim 3.0$ GPa and then shows a monotonic decrease with increasing pressure. The plateau width decreases for the system with smaller lattice constants and shrinks to almost zero for $R = Sm$ . From the $T_{c}$ ( $P$ ) data, we construct the $T_{c}$ evolution map on the height of the As atom from the Fe-plane $h_{As}$ versus lattice-constant $a$ or $c$ plane. It is shown that the characteristic $T_{c}$ variations under pressure for all compounds and the rapid decrease in $T_{c}$ induced by changing the $R$ element from Sm to La can be described by a common $T_{c}$ ( $h_{As}$ , $a$ or $c$ ) surface, suggesting that $T_{c}$ is determined by $h_{As}$ and lattice constant. It is also suggested that there exists an upper limit of the lattice constant $a_{ulm}$ (or $c_{ulm}$ ), above which $d T_{c}$ $/$ $d a$ (or $d T_{c}$ $/$ $d c$ ) changes the sign from positive to negative.

Received 4 March 2013

DOI:https://doi.org/10.1103/PhysRevB.87.235111

Authors & Affiliations

Kiyotaka Miyoshi, Eiko Kojima, Saki Ogawa, Yuta Shimojo, and Jun Takeuchi

Department of Material Science, Shimane University, Matsue 690-8504, Japan

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Vol. 87, Iss. 23 — 15 June 2013

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Figure 1
Temperature dependence of zero-field-cooled dc magnetization measured with a magnetic field of $H = 20$ Oe under various pressures up to (a) 3.5 GPa, (b) 7.0 GPa, and (c) 7.5 GPa for LaFeAsO $_{1 - x}$ F $_{x}$ . The data are intentionally shifted along the longitudinal axis for clarity. The data measured using liquid Ar as a pressure transmitting medium are shown in (c).Reuse & Permissions
Figure 2
Temperature dependence of zero-field-cooled dc magnetization measured with a magnetic field of $H = 20$ Oe under various pressures up to (a) 2.9 GPa and (b) 5.1 GPa for CeFeAsO $_{1 - x}$ F $_{x}$ and (c) 2.9 GPa and (d) 7.0 GPa for PrFeAsO $_{1 - x}$ F $_{x}$ . The data are intentionally shifted along the longitudinal axis for clarity. The data measured using liquid Ar as a pressure transmitting medium are shown in (b) and (d).Reuse & Permissions
Figure 3
Temperature dependence of zero-field-cooled dc magnetization measured with a magnetic field of $H = 20$ Oe under various pressures up to (a) 3.0 GPa and (b) 7.7 GPa for NdFeAsO $_{1 - x}$ F $_{x}$ and up to (c) 2.5 GPa and (d) 7.7 GPa for SmFeAsO $_{1 - x}$ F $_{x}$ . The data are intentionally shifted along the longitudinal axis for clarity. The data measured using liquid Ar as a pressure transmitting medium are shown in (d).Reuse & Permissions
Figure 4
Pressure variations of critical temperature $T_{c}$ for $R$ FeAsO $_{1 - x}$ F $_{x}$ ( $R = La$ , Ce–Sm). The solid lines are guides for the eyes. The data sets measured in different runs are plotted by different symbols. Open and closed diamonds (other symbols) indicate the data obtained by using liquid Ar (Daphne oil 7373) as the pressure transmitting medium.Reuse & Permissions
Figure 5
Plots of $T_{c}$ vs height of the As layer from Fe layer $h_{As}$ for $R$ FeAsO $_{1 - x}$ F $_{x}$ ( $R = La$ , Ce–Sm). The broken line interpolates the data at ambient pressure, which are displayed by large closed diamonds, and corresponds to the variation for the chemical substitution for the $R$ site. Small symbols represent the data obtained from the physical pressure dependence of $T_{c}$ . The $T_{c}$ ( $P$ ) data are transformed to $T_{c}$ ( $h_{As}$ ) data assuming a linear relation with a coefficient $d h_{As}$ $/$ $d P \sim - 3.6 \times 10^{- 3}$ Å GPa $^{- 1}$ extracted from the pressure variations of structural parameters in the literature.[26] The values of $h_{As}$ at ambient pressure can be obtained from the literature.[8, 11, 44, 45]Reuse & Permissions
Figure 6
$T_{c}$ evolution on the $h_{As}$ –lattice-constant (a) $a$ and (b) $h_{As}$ - $c$ planes for $R$ FeAsO $_{1 - x}$ F $_{x}$ . The $T_{c}$ ( $P$ ) data for each system are plotted on the planes after transforming the data, assuming linear relations $h_{As} = -$ 3.6 $\times$ 10 $^{- 3}$ $P$ $+$ $h_{As}$ $(0)$ , $a = - 9.3 \times 10^{- 3} P + a (0)$ , and $c = - 4.7 \times 10^{- 2} P + c (0)$ obtained from the literature.[19, 26] The data at ambient pressure for $R = La$ , Ce-Gd are displayed by large closed diamonds. The solid lines indicate contours of $T_{c}$ , which are drawn by connecting the data point with similar $T_{c}$ . The broken line indicates the upper limit of the lattice constant $a_{ulm}$ ( $h_{As}$ ) $(c_{ulm}$ ( $h_{As}))$ , above which $d T_{c}$ $/$ $d a$ ( $d T_{c}$ $/$ $d c$ ) changes the sign from positive to negative. (c) Three-dimensional plots of $T_{c}$ as a function of $h_{As}$ and $a$ . The solid lines (broken line) indicate(s) contours (a ridge) of the $T_{c}$ ( $h_{As}$ , $a$ ) surface.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Superconductivity under pressure in $R$ FeAsO $_{1 - x}$ F $_{x}$ ( $R$ $=$ La, Ce $-$ Sm) by dc magnetization measurements

Kiyotaka Miyoshi, Eiko Kojima, Saki Ogawa, Yuta Shimojo, and Jun Takeuchi

Phys. Rev. B 87, 235111 – Published 11 June 2013

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Physical Review B

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Superconductivity under pressure in RFeAsO1−xFx (R = La, Ce−Sm) by dc magnetization measurements

Kiyotaka Miyoshi, Eiko Kojima, Saki Ogawa, Yuta Shimojo, and Jun Takeuchi

Phys. Rev. B 87, 235111 – Published 11 June 2013

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Superconductivity under pressure in $R$ FeAsO $_{1 - x}$ F $_{x}$ ( $R$ $=$ La, Ce $-$ Sm) by dc magnetization measurements