[Paper Review] Colossal low-field negative magnetoresistance in CaAl$_{2}$Si$_{2}$-type diluted magnetic semiconductors (Ba,K)(Cd,Mn)$_{2}$As$_{2}$

Bijuan Chen, Zheng Deng+1 more|arXiv (Cornell University)|Jan 19, 2026

Iron-based superconductors research0 citations

TL;DR

The study reports decoupled spin and charge doping in (Ba,K)(Cd,Mn)$_{2}$As$_{2}$ DMSs, showing soft ferromagnetism and colossal negative magnetoresistance near 100% at low fields for high Mn content.

ABSTRACT

We report the magnetic and magnetotransport properties of the layered CaAl$_2$Si$_2$-type diluted magnetic semiconductor (Ba$_{1-x}$K$_x$)(Cd$_{1-y}$Mn$_y$)$_2$As$_2$ over a broad Mn (spin) substitution range of $0.05 \le y \le 0.5$. K substitution introduces hole carriers, whereas Mn provides local moments, resulting in bulk ferromagnetism with Curie temperatures up to $\sim 17$ K. Intrinsic magnetic ordering is further supported by an anomalous Hall contribution and a specific-heat anomaly near $T_{\mathrm{C}}$. A key performance feature is a colossal negative magnetoresistance: for heavily Mn-doped compositions ($y \ge 0.3$), $\mathrm{MR}=[ρ(H)-ρ(0)]/ρ(0)$ reaches approximately $-100\%$ at 2 K and nearly saturates at a relatively low magnetic field of $\sim 0.35\,\mathrm{T}$. The combination of soft ferromagnetism, strong spin-charge coupling, and low-field MR saturation highlights (Ba,K)(Cd,Mn)$_2$As$_2$ as a promising bulk platform for low-temperature magnetoresistive functionalities.

Motivation & Objective

• Explore how decoupled charge (K) and spin (Mn) doping tunes ferromagnetism in CaAl2Si2-type bulk DMS Ba1−xKx(Cd1−yMny)2As2.
• Characterize magnetic, transport, and thermodynamic signatures of ordering across broad Mn substitution (0.05 ≤ y ≤ 0.5).
• Demonstrate the relationship between Mn content, carrier density, and magnetoresistance, especially at low fields.
• Provide evidence for intrinsic magnetic ordering via anomalous Hall effect and specific-heat anomalies near Tc.
• Assess potential of this material family as a bulk platform for low-temperature magnetoresistive applications.

Proposed method

• Synthesize polycrystalline samples via solid-state reaction with controlled K and Mn codoping.
• Characterize structure by room-temperature XRD and Rietveld refinement to confirm CaAl2Si2-type hexagonal structure.
• Measure magnetization M(T) and M(H) to determine Curie temperature and saturation moments.
• Perform Hall effect measurements to identify anomalous Hall contribution and carrier type.
• Obtain specific heat C(T) to detect magnetic ordering signatures near Tc.
• Study resistivity ρ(T) and magnetoresistance MR(H) to evaluate low-field MR behavior across Mn contents.

Fig. 1: Crystal structure and phase characterization of CaAl 2 Si 2 -type (Ba,K)(Cd,Mn) 2 As 2 . a Crystal structure of (Ba,K)(Cd,Mn) 2 As 2 (space group $P\bar{3}m1$ ), composed of CdAs 4 tetrahedra and BaAs 6 octahedra and forming a layered Cd 2 As 2 network. b Powder X-ray diffraction patterns of

Experimental results

Research questions

• RQ1 How does decoupled doping (K for holes, Mn for local moments) influence ferromagnetic ordering in Ba1−xKx(Cd1−yMny)2As2?
• RQ2 What is the Mn content dependence of Tc and Msat in this CaAl2Si2-type DMS?
• RQ3 Can intrinsic magnetic ordering be corroborated by anomalous Hall effect and specific-heat anomalies near Tc?
• RQ4 How does Mn-induced disorder/localization affect magnetoresistance, and is colossal negative MR achievable at low fields?
• RQ5 Is there a practical low-field MR regime suitable for bulk magnetoresistive applications in this system?

Key findings

• Ferromagnetic ordering is achieved with decoupled hole and spin doping, with Tc up to about 17 K at optimal Mn content.
• Anomalous Hall effect and a specific-heat anomaly near Tc support intrinsic ordering.
• Increasing Mn content enhances disorder/localization and drives a colossal negative MR approaching −100% at 2 K, saturating near 0.35 T.
• K-doping lowers resistivity by increasing hole density, while Mn-doping increases resistivity due to disorder effects.
• Tc shows a non-monotonic dependence on Mn content, peaking around y ≈ 0.20 and decreasing at higher Mn levels.
• The lattice parameters expand with K doping and contract with Mn doping, consistent with successful chemical substitution.

Fig. 2: Ferromagnetism and Hall response in (Ba,K)(Cd,Mn) 2 As 2 with decoupled charge and spin doping. a Temperature dependence of magnetization $M(T)$ measured under 500 Oe for the K-doping series (Ba 1-x K x )(Cd 0.9 Mn 0.1 ) 2 As 2 with $x$ =0.01–0.10, showing ferromagnetic ordering; inset: Curi