Magnetic materials with the spinel structure (A2+B23+O4) form the core of numerous magnetic devices, but ZnFe2O4 constitutes a peculiar example where the nature of the magnetism is still unresolved. Susceptibility measurements revealed a cusp around Tc=13K resembling an antiferromagnetic transition, despite the positive Curie-Weiss temperature determined to be ΘCW=102.8(1)K. Bifurcation of field-cooled and zero-field-cooled data below Tc in conjunction with a frequency dependence of the peak position and a non-zero imaginary component below Tc shows it is in fact associated with a spin-glass transition. Highly structured magnetic diffuse neutron scattering from single crystals develops between 50K and 25K 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. Our 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.
@article{arxiv.2208.01431,
title = {Direct visualization of magnetic correlations in frustrated spinel ZnFe$_2$O$_4$},
author = {Jonas Ruby Sandemann and Thomas Bjørn Egede Grønbech and Kristoffer Andreas Holm Støckler and Feng Ye and Bryan C. Chakoumakos and Bo Brummerstedt Iversen},
journal= {arXiv preprint arXiv:2208.01431},
year = {2022}
}