High-temperature susceptibility of cobalt and manganese aluminosilicate glasses

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Abstract
The magnetic susceptibility for 14.3 at.% Mn and 14.3 at.% Co aluminosilicate glasses has been measured via a sensitive pendulum magnetometer from 4 to 300 K in a field of 5 kOe. For temperatures above 80 K a Curie–Weiss law was obeyed in both systems; however, below 80 K strong deviations from this law occurred. From the high-temperature inverse susceptibility, a Bohr magneton number p0 of 5.93 μB for Mn and 4.73 μB for Co was found. These values correspond to the free ion values observed for Mn++ and Co++, respectively. The paramagnetic Curie temperatures ϑ are −117 K for Mn and −44 K for Co. Assuming a cubic closed packed structure to represent our amorphous system, we have analyzed these results with a canonical ensemble for all possible states of the first eleven configurations in which magnetic impurities can be grouped in this structure. Thereby we can explain the deviations from the Curie–Weiss law, ϑ, and p0 and their temperature dependences with nearest neighbor and next nearest neighbor exchanges of −27 and −20 K for Mn and −24 and +5 K for Co.