Recent advances in understanding and manipulating magnetic and electronic properties of Eu$M_2X_2$ ($M$ = Zn, Cd; $X$ = P, As)

TL;DR

This review summarizes recent progress in understanding the magnetic and electronic properties of Eu$M_2X_2$ compounds, highlighting their potential for spintronics and the complex interplay between magnetism and charge transport.

Contribution

The paper provides a comprehensive review of Eu$M_2X_2$ compounds, emphasizing their magnetic, electronic, and transport properties, and discusses future research directions.

Findings

Eu$M_2X_2$ compounds exhibit giant nonlinear anomalous Hall effect.

Colossal magnetoresistance observed in Eu$M_2X_2$ materials.

Carrier density and pressure can tune magnetic and electronic phases.

Abstract

Over the past five years, significant progress has been made in understanding the magnetism and electronic properties of CaAl$_2$Si$_2$-type Eu$M_2X_2$ ($M$ = Zn, Cd; $X$ = P, As) compounds. Prior theoretical work and experimental studies suggested that EuCd$_2$As$_2$ had the potential to host rich topological phases, particularly an ideal magnetic Weyl semimetal state when the spins are polarized along the c axis. However, this perspective is challenged by recent experiments utilizing samples featuring ultra-low carrier densities, as well as meticulous calculations employing various approaches. Nonetheless, the Eu$M_2X_2$ family still exhibit numerous novel properties that remain to be satisfactorily explained, such as the giant nonlinear anomalous Hall effect and the colossal magnetoresistance effect. Moreover, Eu$M_2X_2$ compounds can be transformed from semiconducting antiferromagnets to metallic ferromagnets by introducing a small number of carriers or applying external pressure, and a further increase in the ferromagnetic transition temperature can be achieved by reducing the unit cell volume. These features make the Eu$M_2X_2$ family a fertile platform for studying the interplay between magnetism and charge transport, and an excellent candidate for applications in spintronics. This paper presents a comprehensive review of the magnetic and transport behaviors of Eu$M_2X_2$ compounds with varying carrier densities, as well as the current insights into these characteristics. An outlook for future research opportunities is also provided.