Lattice-Expansion-Driven Stabilization of Helical Magnetic Order in Ru-Doped MnP

TL;DR

This study shows that Ru doping in MnP causes anisotropic lattice expansion, significantly increasing the helical magnetic ordering temperature by stabilizing the helimagnetic ground state through structural distortion.

Contribution

It demonstrates that targeted $b$-axis lattice expansion via chemical doping can robustly stabilize helimagnetism in MnP, revealing a universal linear scaling relationship.

Findings

$T_S$ increases from 51K to 215K with Ru doping.

$T_C$ decreases from 291K to 215K with Ru doping.

Lattice expansion along the $b$-axis correlates linearly with $T_S$ and $T_C$

Abstract

The practical utilization of MnP in chiral spintronic devices is fundamentally constrained by its low helical ordering temperature ($T_{\rm S}$). Here, we demonstrate that Ru substitution in Mn$_{1-x}$Ru$_x$P single crystals drives a highly anisotropic lattice expansion, where the $b$-axis elongation is one-quarter that of the $a$- and $c$-axes ($\sim$ 0.04 \AA). This structural distortion profoundly stabilizes the helical ground state, elevating $T_{\rm S}$ from 51~K to 215~K and the critical field along the [010] direction at 5~K from 2.3 to 30.0~kOe, while suppressing the Curie temperature ($T_{\rm C}$) from 291~K to 215~K. Synthesizing these results with reported data on Mo- and W-doped analogues reveals that $T_{\rm S}$ and $T_{\rm C}$ are governed primarily by the $b$-axis parameter, exhibiting universal linear scaling relationships ($dT_{\rm S}/db = 1.59 \times 10^4\ \text{K\AA}^{-1}$, $dT_{\rm C}/db = 0.69 \times 10^4\ \text{K\AA}^{-1}$) far greater than those associated with the $a$- or $c$-axes. First-principles calculations reveal that the lattice expansion selectively attenuates ferromagnetic coupling while preserving antiferromagnetic interactions between nearest-neighbor Mn atoms, thereby enhancing magnetic frustration and stabilizing helimagnetism. These findings establish chemical pressure via directed $b$-axis engineering as a robust, generalizable paradigm for stabilizing helimagnetism in MnP.