Abstract
The antiferromagnetic layer phase Ca 2MnO 4 doped with 119Sn 4+ has been investigated by Mössbauer spectroscopy. Below the Néel temperature a hyperfine magnetic field transfered on the tin nucleus is observed with saturation value H(0)≅38 kOe. The low value of the transfered field is attributed to the absence of e g electrons on the 3 d orbitals of Mn 4+. Supposing the field to follow the power law H( T) = H(0) D[1 − ( T/ T N )] β as the sublattice magnetizations usually do, the study of the temperature dependence of the field yields β = 0.44 ± 0.10. This value for the critical exponent is in rather good agreement with the value deduced from neutron measurements ( β = 0.38 ± 0.06) as well as with those calculated from three dimensional Heisenberg and Ising models (0.31⩽β⩽0.38). It is anyway very different from the theoretical value for a two dimensional Ising model ( β = 0.125) and from the experimental values for various two-dimensional antiferromagnets isostructural with Ca 2MnO 4 such as K 2MnF 4 ( β = 0.15) or K 2NiF 4 ( β = 0.14).
Published Version
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