Direct Visualization of Magnetic Correlations in Frustrated Spinel ZnFe<sub>2</sub>O<sub>4</sub>
Jonas Ruby Sandemann, Thomas Bjørn Egede Grønbech, Kristoffer Andreas Holm Støckler, Feng Ye, Bryan C. Chakoumakos, Bo B. Iversen
Abstract
Abstract Magnetic materials with the spinel structure (A 2+ B 3+ 2 O 4 ) form the core of numerous magnetic devices, and ZnFe 2 O 4 constitutes a peculiar example where the nature of the magnetism is still unresolved. Susceptibility measurements revealed a cusp around T c = 13 K resembling an antiferromagnetic transition, despite the positive Curie–Weiss temperature determined to be Θ CW = 102.8(1) K. Bifurcation of field‐cooled and zero‐field‐cooled data below T c in conjunction with a frequency dependence of the peak position and a non‐zero imaginary component below T c shows it is in fact associated with a spin‐glass transition. Highly structured magnetic diffuse neutron scattering from single crystals develops between 50 K and 25 K revealing the presence of magnetic disorder which is correlated in nature. Here, the 3D‐mΔPDF method is used to visualize the local magnetic ordering preferences, and ferromagnetic nearest‐neighbor and antiferromagnetic third nearest‐neighbor correlations are shown to be dominant. Their temperature dependence is extraordinary with some flipping in sign and a strongly varying correlation length. The correlations can be explained by orbital interaction mechanisms for the magnetic pathways and a preferred spin cluster. This study demonstrates the power of the 3D‐mΔPDF method in visualizing complex quantum phenomena thereby providing a way to obtain an atomic‐scale understanding of magnetic frustration.