Bulk specimens of the hetærolite solid solution ${\text{Zn}}_x{\text{Mn}}_{3-x}{\text{O}}_4$ 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 ${\text{Mn}}_3{\text{O}}_4$ with an antiferromagnet ${\text{ZnMn}}_2{\text{O}}_4$ wherein distinct magnetic clusters grow and percolate to produce a smooth transition between competing orders.

• Received 22 June 2009

DOI:https://doi.org/10.1103/PhysRevB.80.144422