Anomalous transport properties of the halfmetallic ferromagnets Co2TiSi, Co2TiGe, and Co2TiSn

TL;DR

This study combines theoretical predictions and experimental data to explore the magnetic, transport, and thermoelectric properties of Co2TiZ (Z=Si, Ge, Sn) half-metallic ferromagnets, revealing their potential for spintronic and thermoelectric applications.

Contribution

It provides the first combined theoretical and experimental analysis of Co2TiZ compounds, highlighting their half-metallicity, high Curie temperatures, and promising thermoelectric properties.

Findings

All compounds are half-metallic ferromagnets with high Curie temperatures.

Co2TiSn exhibits 55% negative magnetoresistance at room temperature.

Large Seebeck coefficients are observed, especially in Co2TiSn, over wide temperature ranges.

Abstract

In this work the theoretical and experimental investigations of Co2TiZ (Z = Si, Ge, or Sn) compounds are reported. Half-metallic ferromagnetism is predicted for all three compounds with only two bands crossing the Fermi energy in the majority channel. The magnetic moments fulfill the Slater-Pauling rule and the Curie temperatures are well above room temperature. All compounds show a metallic like resistivity for low temperatures up to their Curie temperature, above the resistivity changes to semiconducting like behavior. A large negative magnetoresistance of 55% is observed for Co2TiSn at room temperature in an applied magnetic field of 4T which is comparable to the large negative magnetoresistances of the manganites. The Seebeck coefficients are negative for all three compounds and reach their maximum values at their respective Curie temperatures and stay almost constant up to 950 K. The highest value achieved is -52muV/K m for Co2TiSn which is large for a metal. The combination of half-metallicity and the constant large Seebeck coefficient over a wide temperature range makes these compounds interesting materials for thermoelectric applications and further spincaloric investigations.