Boron Content and the Superconducting Critical Temperature of Carbon-Based Materials

TL;DR

This study investigates the magnetic and superconducting properties of boron-doped carbon-based materials, revealing a linear increase in critical temperature with boron content and identifying signatures of granular superconductivity.

Contribution

It provides new experimental data on magnetization and superconductivity in BN-C and B4C-C mixtures, linking boron concentration to critical temperature enhancement.

Findings

Magnetization shows thermal hysteresis around a metamagnetic transition.

Superconducting critical temperature (Tc) increases linearly with boron content.

Evidence of granular superconductivity in magnetization loops.

Abstract

In this paper, we present results on magnetization properties of boron nitride-carbon (BN-C) and boron carbide-carbon (B4C-C) granular mixtures. The temperature-dependent magnetization for field-cooled during cooling and field-cooled during warming shows a kind of thermal hysteresis that is always seen around a metamagnetic phase transition from an antiferromagnetic martensite to a ferromagnetic austenite phase. The low-temperature magnetization has an upward turn that can be attributed to superparamagnetism, diamagnetic shielding, and trapped flux characteristic to high-temperature superconducting materials. After subtracting the diamagnetic background, the field-dependent magnetization loops M(B) are ferromagnetic-like, more significant for the BN-C than for the B4C-C mixture. In addition, the magnetization loops show the kink feature characteristic to granular superconductivity. The irreversibility temperature for a B4C-C mixture having 37.5 wt% B is Tc = 76 K. Combining our data with previous results on B-doped diamond and Q-carbon, we find that Tc increases linearly with the B concentration.