Magnetic properties on MnO⋅Al2O3⋅SiO2 glasses

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Abstract
The magnetic susceptibility of concentrated Mn aluminosilicate glasses has been measured from 1.5 to 300 K. The susceptibilities above ∠50 K follow a Curie‐Weiss behavior characterized by a large negative paramagnetic Curie temperature, indicating strong antiferromagnetic interactions among the manganese ions. Below ∠50 K the susceptibilities exhibit a superparamagnetic type behavior which terminates in a sharp peak at 3.3 to 6.5 K. In general with increasing Mn concentration the peak shifts to a higher temperature while the peak susceptibility decreases. Although the sharp peaks in the susceptibility seem to indicate the onset of long range antiferromagnetic order, we show that this behavior can be explained quantitatively by postulating that these glasses contain small (∠50 Å) manganese rich monodomains (which order antiferromagnetically well above the peak temperature) separated by manganese poor paramagnetic regions, and applyin Néel theory of small antiferromagnetic particles. The crucial parameters of this theory are the anisotropy energy, K, the volume, V, and the magnetic moment μ, of the monodomains. For very reasonable values of these parameters (KV∠10−15 erg, μ∠200 μB) quantitative agreement with the experimental data is obtained.

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