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<p>In NiO the Ni makes an FCC structure, you cannot have an antiferromagnetic arrangement in a triangular lattice (for example in 1,1,1 planes), even less in the FCC, which is triangular in many planes, so there is what is called "geometrical frustration"<br>
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On the other hand, in Cr you have the "Cr up" and "Cr dn" alternated and you can have a clear antiferromagnetic arrangement<br>
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Pablo<br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>De:</b> Wien <wien-bounces@zeus.theochem.tuwien.ac.at> en nombre de Abderrahmane Reggad <jazairdz@gmail.com><br>
<b>Enviado:</b> miércoles, 8 de junio de 2016 05:43 a. m.<br>
<b>Para:</b> wien@zeus.theochem.tuwien.ac.at<br>
<b>Asunto:</b> [Wien] Why the antiferromagnetic structure of Cr is still cubic</font>
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<div style="font-size:12.8px">Dear wien2k users</div>
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<div style="font-size:12.8px">I have read that the antiferromagnetic ordering is accompanied with a little structural distortion as in the case of NiO. This latter is characterized by a distortion from NaCl to rhomboherdral structure; but for the chromide Cr
the structure is still cubic when there is a magnetic transition from paramagnetic to antiferromagnetic state.</div>
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<div style="font-size:12.8px">Best regards</div>
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<div><font size="2"><span style="color:rgb(0,0,255)">Mr: A.Reggad</span>
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<span style="background-color:rgb(238,238,238)"><span style="color:blue">Laboratoire de Génie Physique</span></span><br>
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<font size="2"><span style="color:rgb(0,0,255)">Université Ibn Khaldoun - Tiaret</span><br>
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<div><font size="2"><span style="font-family:monospace"><span style="color:rgb(0,0,255)">Algerie</span></span></font><br>
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