Structural characterization and magnetic properties of chromium jarosite KCr 3 (OD) 6 (SO 4 ) 2 .

Potassium chromium jarosite, KCr ₃ (OH) ₆ (SO ₄ ) ₂ (Cr-jarosite), is considered a promising candidate to display spin liquid behavior due to the strong magnetic frustration imposed by the crystal structure. However, the ground state magnetic properties have been debated, since Cr-jarosite is notoriously non-stoichiometric. Our study reports the magnetic properties for deuterated KCr ₃ (OD) ₆ (SO ₄ ) ₂ on chemically well-defined samples, which have been characteried by a combination of powder X-ray diffraction, neutron diffraction, solid state NMR spectroscopy, and scanning electron microscopy with energy dispersive spectroscopy. Eight polycrystalline samples, which all contained only 1-3% Cr vacancies were obtained. However, significant substitution (2-27%) of potassium with H ₂ O and/or H ₃ O ⁺ was observed and resulted in pronounced stacking disorder along the c-axis. A clear second-order transition to an antiferromagnetically ordered phase at T _N = 3.8(1) K with a small net moment of 0.03 μ _B per Cr ³⁺ -ion was obtained from vibrating sample magnetometry and temperature dependent neutron diffraction. The moment is attributed to spin canting caused by the Dzyaloshinskii-Moriya interaction. Thus, our experimental results imply that even ideal potassium chromium jarosite will exhibit magnetic order below 4 K and therefore it does not qualify as a true spin liquid material.