Electron spin resonance of Mn3O4 defects in MnOa)

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Abstract
Here we report the first observation of an electron spin resonance (ESR) line due to the Mn3O4 impurity in MnO. Using this ESR line (g≂2.005, linewidth ΔH≂100 Oe) as a probe, we have shown that Mn3O4 is primarily concentrated on the surface of MnO. The temperature dependence of the ESR line was investigated from 20 to 150 K. Anomalous changes in Hr (resonance field) and ΔH are observed near 42 K, the ferrimagnetic ordering temperature of Mn3O4. Above 42 K, Hr is temperature-independent, but ΔH shows noticeable changes near 102 and 118 K (TN for MnO). From the observed change in g below 42 K, an anisotropy of 90 Oe for Mn3O4 in MnO is determined and this anisotropy is consistent with the observed ΔH. This anisotropy, about 10−2 times the anisotropy of pure Mn3O4, may be primarily due to exchange anisotropy at the Mn3O4–MnO interface.