Tuning the Magnetically Segregated Nanolayering in Mn–Ni–As Intermetallics

Bruno Gonano,Gwladys Steciuk,Francois Guillou,Dipankar Saha,Denis Pelloquin,Helmer Fjellvåg,Øystein Slagtern Fjellvåg

doi:10.1021/acs.chemmater.1c00760

Abstract

2D materials exhibiting alternating ferro- and non-ferromagnetic layers are highly sought due to their potential for applications. In this work, we demonstrate, through the use of robust methodology, the existence of single-phase, Mn1–xNixAs (0.25 ≤ x ≤ 0.50), with a unique intrinsic nanostructuring where the thickness of MnAs and NiAs nanolayers can be tuned via the composition, x. We describe a periodic variation of nanolayers of edge-sharing MnAs6 and NiAs6 octahedra layers with thicknesses ranging from 1 to 6 octahedra, 2–16 Å. These crystalline structures are modulated and fully described based on 3D electron diffraction and neutron diffraction. Moreover, by X-ray magnetic circular dichroism, an elemental and orbital-specific technique, we probe the 3d magnetic moments of Mn and Ni. We unveil that the nanosegregated MnAs and NiAs layers behave very differently, with the magnetic moment of manganese being one order of magnitude greater than that of nickel. This study opens the path to a completely new class of materials with intrinsic layers of high and low magnetization with potential applications within spintronics.

Highlights

The benefits of fundamental research as a guide toward applications and innovations are since long demonstrated by magnetic materials; the transfer process is still ongoing. 3d-based intermetallic materials can be brought at the verge of stability between different magnetic, crystal, or electronic structures, leading in turn to unusual phase transitions potentially involving changes in local magnetic moments and discontinuities in magnetic, lattice, or electronic entropies
The physicochemical properties of these compounds are determined by the nature of chemical bonding, the crystal structure,[11] and especially the dimensionality[12] of the crystal structure, which has a major impact on the properties
We initiated our study of Mn1−xNixAs samples (x = 0.25, 0.33, 0.40, and 0.50; average structure P63/mmc) in the superstructure range reported by Fjellvåg et al.[52] by high-angle annular dark field (HAADF) imaging, allowing good elemental contrasts for Mn and Ni

Summary

INTRODUCTION

The benefits of fundamental research as a guide toward applications and innovations are since long demonstrated by magnetic materials; the transfer process is still ongoing. 3d-based intermetallic materials can be brought at the verge of stability between different magnetic, crystal, or electronic structures, leading in turn to unusual phase transitions potentially involving changes in local magnetic moments and discontinuities in magnetic, lattice, or electronic entropies. 2D materials with magnetic layers are interesting due to their strong magnetic anisotropy and electronic anisotropy, leading to complex phenomena such as charge and spin density waves,[13−15] staircase-like magnetism,[16] magnetic exchange bias effect,[17] or even superconductivity.[18,19] In addition to the fundamental interest, such 2D materials hold great potential for applications in, e.g., data storage and spintronics.[20] Materials presenting an alternation of magnetic and non-magnetic layers may act as spin valves[21−24] or as magnetic tunnel junctions[25−28] and are currently widely exploited for MRAM29,30 (magnetic random access memory) In this field, two-dimensional structures are desired but just very few crystalline materials display the structural features of stacked ferromagnetic and nonferromagnetic layers with sufficient control of layer thickness and spacing. The very understanding of the connection between modulated composition and magnetic properties in Mn1−xNixAs is important and interesting

EXPERIMENTAL AND METHODS

RESULTS AND DISCUSSION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES