Vortex pinning and magnetic phase diagram of EuRbFe ₄ As ₄ iron-based superconductor

Abstract

Abstract We performed systematic AC susceptibility and magnetic moment measurements to investigate the vortex dynamics and pinning in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>E</mml:mi> <mml:mi>u</mml:mi> <mml:mi>R</mml:mi> <mml:mi>b</mml:mi> <mml:mi>F</mml:mi> <mml:msub> <mml:mi>e</mml:mi> <mml:mn>4</mml:mn> </mml:msub> <mml:mi>A</mml:mi> <mml:msub> <mml:mi>s</mml:mi> <mml:mn>4</mml:mn> </mml:msub> </mml:math> single crystals as a function of temperature, frequency, and DC magnetic field. The vortex solid-liquid line was determined, and it can be fitted well with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>H</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>p</mml:mi> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mi>H</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>0</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:msub> <mml:mi>t</mml:mi> <mml:mi>p</mml:mi> </mml:msub> <mml:mrow> <mml:msup> <mml:mo stretchy="false">)</mml:mo> <mml:mi>β</mml:mi> </mml:msup> </mml:mrow> </mml:math> using β = 1.74 ± 0.1–1.91 ± 0.1, where T p is the peak position on an imaginary part of the AC susceptibility plot ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi>χ</mml:mi> <mml:mo>′′</mml:mo> </mml:msup> </mml:math> ), <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>t</mml:mi> <mml:mi>p</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>p</mml:mi> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>c</mml:mi> </mml:msub> </mml:math> for H <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∥</mml:mo> </mml:math> ab. It indicates a rather high pinning strength of the vortex system. The activation energy U 0 was determined from thermally activated flux creep theory and reached 6700 ± 1100 K at low fields, suggesting strong vortex pinning. A field dependence of U 0 (H <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∥</mml:mo> </mml:math> ab) ∼ H a with a = 0.47(4) suggests thermally activated plastic pinning or caused by planar defects. Magnetic moment measurements also confirmed strong pinning in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>E</mml:mi> <mml:mi>u</mml:mi> <mml:mi>R</mml:mi> <mml:mi>b</mml:mi> <mml:mi>F</mml:mi> <mml:msub> <mml:mi>e</mml:mi> <mml:mn>4</mml:mn> </mml:msub> <mml:mi>A</mml:mi> <mml:msub> <mml:mi>s</mml:mi> <mml:mn>4</mml:mn> </mml:msub> </mml:math> superconductor, and the superconducting response gives the main contribution to the M(H) hysteresis. Additionally, we show long-range ordering of the Eu 2 + sublattice according to the AC susceptibility measurement data.

Topics & Concepts