Transport and magnetotransport properties of cold-pressed CrO$_2$ powder, prepared by hydrothermal synthesis

TL;DR

This study investigates the transport and magnetoresistance properties of hydrothermally synthesized CrO₂ powder, revealing significant low-temperature negative magnetoresistance due to spin-dependent tunneling between magnetic grains.

Contribution

First detailed analysis of transport and magnetotransport in hydrothermally synthesized CrO₂ powder with granular structure and magnetic properties.

Findings

Large negative magnetoresistance at low temperatures (-20% at 5 K)

Resistance exhibits non-metallic behavior across 4-450 K

Magnetoresistance decreases rapidly above 40 K

Abstract

Submicron powder of CrO$_2$ was prepared by hydrothermal synthesis method from chromium trioxide. Particles obtained were of rounded form with mean diameter about 120 nm. The powder (stabilized with thin surface layer of \beta-CrOOH) has been characterized by structural, X-ray and magnetic measurements. The powder (with Curie temperature about 385 K) was cold-pressed and its transport and magnetotransport properties have been measured in the temperature range 4--450 K in magnetic field up to 1.6 T. The samples studied is characterized by non-metallic temperature behavior of resistance and large negative magnetoresistance (MR) in low temperature range. At T=5 K the MR magnitude has been -17% at H=0.3 T and -20% at H=1.4 T. Its magnitude decreased fast with increase in temperature reducing to 0.3% and less for T>200 K. It is shown that this MR behavior is inherent for a system of magnetic grains with spin-dependent intergrain tunnelling. Some peculiarities of MR behavior in low-temperature range (below 40 K) can be associated with percolating character of tunnelling conductivity of this granular system under conditions of availability of only few conducting current paths through the sample.