Effect of Ni doping on vortex pinning in CaK(Fe 1-xNi x) 4As 4 single crystals

N. HABERKORN; MINGYU XU ; W. MEIER; J. SCHMIDT; S. L. BUD'KO; P. C. CANFIELD

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Lugar: New York; Año: 2019 vol. 100 p. 64524 - 64535

1098-0121

We study the correlation between chemical composition and vortex dynamics in Ni-doped CaK(Fe1-xNix)4As4 (x = 0, 0.015, 0.025, 0.03 and 0.05) single crystals by performing measurements of the critical current densities Jc and the flux creep rates S. The magnetic relaxation of all the crystals is well described by the collective creep theory. The samples display a glassy exponent, μ, within the predictions for vortex bundles in a weak pinningscenario and relatively small characteristic pinning energy (U0 < 100 K). The undoped crystals display modest Jc values at low temperatures and high magnetic fields applied along the c-axis. Jc (T) dependences at high fields display an unusual peak. The enhancement in Jc (T) matches with an increase in U0 and the appearance of a second peak in the magnetization (SPM). As Ni doping increases whereas there is a monotonic decrease in Tc there is a non-monotonic change in Jc. Initially Jc increases, reaching a maximum value for x = 0.015, and then Jc decreases for x ≥ 0.025. This change in Jc(x) is coincident with the onset of antiferromagnetic order. The magnetic field dependence of Jc(H) also manifests a change in behavior between these xvalues. The analysis of the vortex dynamics for small and intermediate magnetic fields shows a gradual evolution in the glassy exponent μ with Ni-content, x. This implies that there is no appreciable change in the mechanism that determines the vortex relaxation for Ni-doped samples.