IsomorphousPrT2B2C(T=Co,Ni,Pt)single crystals: Structural, transport, and magnetic properties

Abstract

The full substitution of Ni by Co and Pt enclosed in the same crystalline structure $(I4∕mmm)$ of Pr-based compounds have been investigated. The structural characteristics, magnetic properties, and magnetoresistance of $\mathrm{Pr}{\mathrm{Co}}_{2}{\mathrm{B}}_{2}\mathrm{C}$, $\mathrm{Pr}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$, and $\mathrm{Pr}{\mathrm{Pt}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ single crystals were studied to determine the reason for the absence or presence of superconductivity in those compounds. An antiferromagnetic transition was found for $\mathrm{Pr}{\mathrm{Co}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ at about $8.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, where the easy magnetization axis is along the $c$-crystallographic direction whereas in $\mathrm{Pr}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ the easy magnetization was at the $ab$ plane. In $\mathrm{Pr}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ a small magnetization without traces of saturation is found when it is measured up to $18\phantom{\rule{0.3em}{0ex}}\text{Tesla}$ of applied magnetic field. This behavior suggests a screening effect as a result of a moderate hybridization between the conduction band and Pr ions. Superconductivity occurs in $\mathrm{Pr}{\mathrm{Pt}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ at about $6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The Pt-Pt distance and internal bonding angles are similar to those observed in the superconducting Ni-based compounds. Magnetoresistance measurements show positive and quadratic behavior $(\ensuremath{\Delta}\ensuremath{\rho}∕{\ensuremath{\rho}}_{0}\ensuremath{\sim}a{H}^{2})$ suggesting a spin fluctuation system. In the $\mathrm{Pr}{\mathrm{Pt}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ compound the electronic mean free path is smaller than the BCS coherence length $(\ensuremath{\iota}⪡\ensuremath{\epsilon})$ suggesting a dirty type II superconductor.