Adriana E. Martinez and Keshav Shrestha Department of ...
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Magnetic Properties of Eu x Ca 1-x Fe 2 As 2 (0 ≤ x ≤ 1) Superconductor Adriana E. Martinez and Keshav Shrestha Department of Chemistry and Physics, West Texas A&M University, Canyon, TX Abstract Method Results and Discussion Summary References We have investigated evolution of magnetic properties of Eu x Ca 1−x Fe 2 As 2 (0 ≤ x ≤ 1) crystals at low-temperatures down to 2 K. Magnetic susceptibility increases while lowering temperature, showing a typical paramagnetic behavior. At low-temperature, there exists a sharp anomaly at T N = 15 - 19 K, which arises due to the Eu 2+ antiferromagnetic ordering. However, there is no clear evidence for the existence of spin-density wave (SDW) due to the Fe-moments. Temperature dependence of the susceptibility data is analyzed using the Curie-Weiss model and determined the Curie constant (C) and Weiss temperature (θ). It is found that both C and θ parameters vary linearly with increasing x. The obtained results will be compared with other published data. Introduction Recent discovery of a new class of iron-based superconductor (IBSC) in 2008 with the critical temperature up to 55 K has stimulated superconductivity research. In IBSC, the Fe-moments arranged in antiferromagnetic order and they appear as a spin- density wave (SDW) order. In general, the suppression of SDW either by doping or external pressure leads to an induction of superconductivity in these materials. There are different kinds of IBSCs, such as 1111, 122, 11, etc. Here, we have focused our studies in 122 family, namely Eu x Ca 1−x Fe 2 As 2 . Both EuFe 2 As 2 and CaFe 2 As 2 are the members of the 122-system in which the SDW order show up at T SDW ∼ 190 K and 170 K, respectively [1]. In addition, there exists another anomaly in EuFe 2 As 2 at ∼19 K due to Eu 2+ antiferromagnetic order. At ambient pressure, both CaFe 2 As 2 and EuFe 2 As 2 samples do not show superconducting properties. While applying pressure, the SDW transition is gradually suppressed and superconductivity with T c ∼ 10 K is induced in CaFe 2 As 2 and T c ∼ 30 K in EuFe 2 As 2 . In our recent report [2], we have investigated electrical transport properties of high-pressure Eu x Ca 1−x Fe 2 . In this work, we have focused mainly on how magnetic properties of CaFe 2 As 2 change upon Eu-doping. High-quality single crystals of Eu x Ca 1−x Fe 2 As 2 were grown using the FeAs flux method as described in our previous report [2]. Magnetic properties were measured through a magnetic properties measurement system (MPMS, Quantum Design) with an applied field of 0.1 T along the c-axis. Magnetic susceptibility data are analyzed using the Curie-Weiss model. According to this law, the temperature dependence of the magnetic susceptibility () is given by χ T = C T−θ , (1) where χ T is magnetic susceptibility at temperature T, C is the Curie-Weiss constant, and is the Weiss temperature. Figure 1. Magnetic susceptibility () vs. temperature plot for Eu x Ca 1−x Fe 2 As 2 . (T) increases gradually while decreasing temperature. In higher x, there exist a sharp anomaly at T N ∼ (15 - 19 K), which arises due to Eu 2+ antiferromagnetic spin ordering, as indicated by the arrow. Inset: (T) data for the EuFe 2 As 2 (x = 1) sample showing T N . The red curve is the best-fit curve using the Curie-Weiss model (Eq. [1]). Figure 2. Inverse susceptibility, 1/ vs. Temperature graphs for Eu x Ca 1−x Fe 2 As 2 samples at (a) x = 0.31, (b) x = 0.65, (c) x = 0.82, and (d) x = 0.92. 1/ increases linearly with temperature, consistent with the Curie-Weiss behavior. The arrow shows the Eu 2+ antiferromagnetic order. The solid red lines are the best-fit lines using the Curie-Weiss law [Eq. (1)]. Figure 3. The best fit parameters, (a) θ (K) and (b) C plotted as a function of x. Both parameters vary almost linearly with x, as shown by the dashed lines. Contact Information Keshav Shrestha, PhD Assistant Professor of Physics Department of Chemistry and Physics West Texas A&M University Email: [email protected] Adriana E. Martinez Department of Mechanical Engineering West Texas A&M University Email: [email protected] 1. L. Harnagea, et al., J. Phys.: Condens. Matter 30 415601 (2018). 2. K. Shrestha, et al., Supercond. Sci. Technol. 33 095010 (2020). Acknowledgements We would like to thank the Ronald McNair Research program, the Paul Engler College of Agriculture and Natural Sciences, and the Welch Foundation (Grant No. AE-025), and Killgore Faculty Research Grant for proving the financial support for this research. Results and Discussion We have investigated the magnetic properties of Eu x Ca 1-x Fe 2 As 2 samples. Susceptibility () of all the samples show the Curie- Weiss behavior, i. e., that 1/ varies linearly with temperature. (T) does not show any evidence of the spin-density wave transition due to Fe-moments. However, there exists an anomaly due to the antiferromagnetic spin ordering of Eu 2+ spins. We have analyzed the (T) data using the Curie-Weiss model. The best-fit parameters, the Weiss-temperature (θ) and Curie constant (C) vary almost linearly with the Eu-doping content.
Transcript of Adriana E. Martinez and Keshav Shrestha Department of ...
Magnetic Properties of EuxCa1-xFe2As2 (0 ≤ x ≤ 1) SuperconductorAdriana E. Martinez and Keshav Shrestha
Department of Chemistry and Physics, West Texas A&M University, Canyon, TX
Abstract
Method
Results and Discussion
Summary
References
We have investigated evolution of magnetic properties ofEuxCa1−xFe2As2 (0 ≤ x ≤ 1) crystals at low-temperatures down to 2K. Magnetic susceptibility increases while lowering temperature,showing a typical paramagnetic behavior. At low-temperature,there exists a sharp anomaly at TN = 15 - 19 K, which arises due tothe Eu2+ antiferromagnetic ordering. However, there is no clearevidence for the existence of spin-density wave (SDW) due to theFe-moments. Temperature dependence of the susceptibility data isanalyzed using the Curie-Weiss model and determined the Curieconstant (C) and Weiss temperature (θ). It is found that both C andθ parameters vary linearly with increasing x. The obtained resultswill be compared with other published data.
Introduction
Recent discovery of a new class of iron-based superconductor(IBSC) in 2008 with the critical temperature up to 55 K hasstimulated superconductivity research. In IBSC, the Fe-momentsarranged in antiferromagnetic order and they appear as a spin-density wave (SDW) order. In general, the suppression of SDWeither by doping or external pressure leads to an induction ofsuperconductivity in these materials. There are different kinds ofIBSCs, such as 1111, 122, 11, etc. Here, we have focused our studiesin 122 family, namely EuxCa1−xFe2As2 . Both EuFe2As2 andCaFe2As2 are the members of the 122-system in which the SDWorder show up at TSDW ∼ 190 K and 170 K, respectively [1]. Inaddition, there exists another anomaly in EuFe2As2 at ∼19 K due toEu2+ antiferromagnetic order. At ambient pressure, both CaFe2As2
and EuFe2As2 samples do not show superconducting properties.While applying pressure, the SDW transition is gradually suppressedand superconductivity with Tc ∼ 10 K is induced in CaFe2As2 and Tc
∼ 30 K in EuFe2As2. In our recent report [2], we have investigatedelectrical transport properties of high-pressure EuxCa1−xFe2. Inthis work, we have focused mainly on how magnetic properties ofCaFe2As2 change upon Eu-doping.
High-quality single crystals of EuxCa1−xFe2As2 were grown usingthe FeAs flux method as described in our previous report [2].Magnetic properties were measured through a magnetic propertiesmeasurement system (MPMS, Quantum Design) with an appliedfield of 0.1 T along the c-axis. Magnetic susceptibility data areanalyzed using the Curie-Weiss model. According to this law, thetemperature dependence of the magnetic susceptibility (𝜒) is givenby
χ T =C
T−θ, (1)
where χ T is magnetic susceptibility attemperature T, C is the Curie-Weiss constant, and 𝛉 is the Weisstemperature.
Figure 1. Magnetic susceptibility (𝜒) vs. temperature plot forEuxCa1−xFe2As2 . 𝜒(T) increases gradually while decreasingtemperature. In higher x, there exist a sharp anomaly at TN ∼ (15 -19 K), which arises due to Eu2+ antiferromagnetic spin ordering, asindicated by the arrow. Inset: 𝜒 (T) data for the EuFe2As2 (x = 1)sample showing TN. The red curve is the best-fit curve using theCurie-Weiss model (Eq. [1]).
Figure 2. Inverse susceptibility, 1/𝜒 vs. Temperature graphs forEuxCa1−xFe2As2 samples at (a) x = 0.31, (b) x = 0.65, (c) x = 0.82,and (d) x = 0.92. 1/𝜒 increases linearly with temperature, consistentwith the Curie-Weiss behavior. The arrow shows the Eu2+
antiferromagnetic order. The solid red lines are the best-fit linesusing the Curie-Weiss law [Eq. (1)].
Figure 3. The best fit parameters, (a) θ (K) and (b) C plotted as a function of x. Both parameters vary almost linearly with x, as shown by the dashed lines.
Contact Information
Keshav Shrestha, PhDAssistant Professor of PhysicsDepartment of Chemistry and PhysicsWest Texas A&M UniversityEmail: [email protected]
Adriana E. MartinezDepartment of Mechanical EngineeringWest Texas A&M UniversityEmail: [email protected]
1. L. Harnagea, et al., J. Phys.: Condens. Matter 30 415601 (2018).2. K. Shrestha, et al., Supercond. Sci. Technol. 33 095010 (2020).
Acknowledgements
We would like to thank the Ronald McNair Research program, thePaul Engler College of Agriculture and Natural Sciences, and theWelch Foundation (Grant No. AE-025), and Killgore Faculty ResearchGrant for proving the financial support for this research.
Results and Discussion
We have investigated the magnetic properties of EuxCa1-xFe2As2
samples. Susceptibility (𝜒) of all the samples show the Curie-Weiss behavior, i. e., that 1/𝜒 varies linearly with temperature.
𝜒 (T) does not show any evidence of the spin-density wavetransition due to Fe-moments. However, there exists an anomalydue to the antiferromagnetic spin ordering of Eu2+ spins.
We have analyzed the 𝜒 (T) data using the Curie-Weiss model.The best-fit parameters, the Weiss-temperature (θ) and Curieconstant (C) vary almost linearly with the Eu-doping content.
