Intrinsic exchange bias in Zn$_x$Mn$_{3-x}$O$_4$ ($x \leq 1$) solid solutions

TL;DR

This study investigates the intrinsic exchange bias in Zn$_x$Mn$_{3-x}$O$_4$ solid solutions, revealing nanoscale magnetic phase separation and complex magnetic behavior without long-range order, through comprehensive neutron diffraction and magnetic measurements.

Contribution

It demonstrates intrinsic exchange bias in Zn$_x$Mn$_{3-x}$O$_4$ due to nanoscale magnetic phase separation, providing new insights into magnetic interactions in mixed-valence oxide systems.

Findings

Samples with $x$ = 0.25, 0.5, 0.75 show shifted hysteresis loops at low temperature.

Magnetic behavior arises from nanoscale mixture of ferrimagnetic and antiferromagnetic regions.

The material is distinguished from a pure spin glass by magnetization measurements.

Abstract

Bulk specimens of the hetaerolite solid solution Zn$_x$Mn$_{3-x}$O$_4$, with $x$ = 0, 0.25, 0.5, 0.75, and 1 have been prepared as homogeneous, phase-pure polycrystalline samples as ascertained by neutron diffraction measurements. Samples with $x$ = 0.25, 0.5, and 0.75 exhibit shifted magnetic hysteresis loops at low temperature, characteristic of exchange bias typically seen in magnetic composites. We propose that the unusual magnetic behavior arises as a result of a nanoscale mixture of ferrimagnetic and antiferromagnetic regions that are distinct but lack long-range order. While some glassy behavior is seen in AC magnetic measurements, its magnitude is not sufficient to account for the observed dramatic exchange bias. Furthermore, isothermal and thermoremanent magnetization measurements distinguish this material from a pure spin glass. The title system offers insights into the alloying of a ferrimagnet Mn$_3$O$_4$ with an antiferromagnet ZnMn$_2$O$_4$ wherein distinct magnetic clusters grow and percolate to produce a smooth transition between competing orders.