# Robust magnetic polaron percolation in the antiferromagnetic CMR system EuCd2P2

## TL;DR

The study reveals that colossal magnetoresistance in EuCd2P2 arises from magnetic polarons percolating through an antiferromagnetic matrix.

## Contribution

The paper provides direct evidence that CMR in EuCd2P2 is caused by magnetic polaron percolation.

## Key findings

- Electronic and magnetic phase separation occurs below T* ≈ 2TN.
- Magnetic polarons with sizes of ~6−10 nm form and percolate in the paramagnetic regime.
- Negative magnetoresistance emerges at a universal critical magnetization.

## Abstract

The interplay between magnetism and charge transport is central to understanding colossal magnetoresistance (CMR), a phenomenon well studied in ferromagnets. Recently, antiferromagnetic (AFM) EuCd2P2 has attracted considerable interest due to its remarkable CMR, for which magnetic fluctuations and the formation of ferromagnetic clusters have been proposed as key mechanisms. Here we provide direct evidence that these effects originate from the formation and percolation of magnetic polarons. We employ a complementary set of sensitive probes that allows for a direct comparison of electronic and magnetic properties on multiple time scales revealing pronounced electronic and magnetic phase separation below T* ≈ 2TN. These measurements indicate an inhomogeneous, percolating electronic system below T* and well above the magnetic ordering temperature TN = 11 K. In applied magnetic fields, the onset of the pronounced negative MR in the paramagnetic regime emerges at a universal critical magnetization. The characteristic size of the magnetic polarons near the percolation threshold is estimated to be ~6−10 nm. Our results establish dynamic polaron percolation within an AFM matrix as the microscopic origin of CMR in EuCd2P2, providing a unified framework for magnetotransport in Eu-based correlated semiconductors.