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MnSiAlthough your formulation is correct, up to eq. 12 it looks to me that it is clearer if you spell it out like this Dipolar field in the paramagnetic phase, in external field H, in SI units, is {$ {\mathbf B}_d= \sum_{i} {\mathbf D}_{i} \frac {v_c} z {\mathbf \chi\, H} $} where {$v_c$} is the unit cell volume and {$z$} is the number of Mn ions per unit cell. We can define a dipolar tensor A d such that {$ {\mathbf B}_d= {\mathbf A}_d {\mathbf \chi \, H}$} The contact field in the same conditions is {$ {\mathbf B}_c= \sum_{i\in {\rm n.n.}} {\mathbf a}_{c,i} \frac {v_c} z {\mathbf \chi\, H} $} We can define again a contact tensor A c such that {$ {\mathbf B}_c= {\mathbf A}_{c} {\mathbf \chi\, H} $} In the ordered phase, in zero external field, in view of the very long wave-length of the helix, within a cell we can approximate the helix to a local ferromagnetic structure, with collinear moments m (e.g. from neutron scattering?) on each Mn and write the contact field as {$ {\mathbf B}_c= \sum_{i\in {\rm n.n.}} {\mathbf a}_{c,i} {\mathbf m}=\frac z {v_c} {\mathbf A}_{c} {\mathbf m} $} This formulation cures a problem in Eq. 12: the macroscopic magnetization of a mole of helix is zero and the expression {$V_{mole} \mathbf M$} is at least ambiguous. |