ASb3Mn9O19 (A = K or Rb): New Mn-Based Two-Dimensional Magnetoplumbites with Geometric and Magnetic Frustration

TL;DR

This study reports the discovery of the first Mn-based magnetoplumbite with pnictogen elements, exhibiting geometric and magnetic frustration, short-range spin order, and complex magnetic behaviors at low temperatures.

Contribution

It introduces a new class of Mn-based magnetoplumbites involving Sb, revealing geometric frustration and unique magnetic properties not previously observed in this family.

Findings

First Mn-based magnetoplumbite with Sb elements.

Presence of geometric and magnetic frustration.

Evidence of short-range magnetic order and two-dimensional correlations.

Abstract

Magnetoplumbites are one of the most broadly studied families of hexagonal ferrites, typically with high magnetic ordering temperatures, making them excellent candidates for permanent magnets. However, magnetic frustration was rarely observed in magnetoplumbites. Herein, we report the discovery, synthesis and characterization of the first Mn-based magnetoplumbite, as well as the first magnetoplumbite involving pnictogens (Sb), ASb3Mn9O19 (A = K or Rb). The Mn3+ (S = 2) cations, further confirmed by DC magnetic susceptibility and X-ray photoelectron spectroscopy, construct three geometrically frustrated sublattices, including Kagome, triangular and puckered honeycomb lattices. Magnetic properties measurements revealed strong antiferromagnetic spin-spin coupling as well as multiple low-temperature magnetic features. Heat capacity data did not show any prominent lambda-anomaly, suggesting minimal associated magnetic entropy. Moreover, neutron powder diffraction implied the absence of long-range magnetic ordering in KSb3Mn9O19 down to 3 K. However, several magnetic peaks were observed in RbSb3Mn9O19 at 3 K, corresponding to an incommensurate magnetic structure. Interestingly, strong diffuse scattering was seen in the neutron powder diffraction patterns of both compounds at low angles, and was analyzed by reverse Monte Carlo refinements, indicating short-range spin ordering related to frustrated magnetism as well as two-dimensional magnetic correlations in ASb3Mn9O19 (A = K or Rb).