[Wien] Why the antiferromagnetic structure of Cr is still cubic

[Juan Manuel Perez Mato]

This discussion may be very misleading. The concept of frustation is very popular, but whatever geometrical frustation may exist in a fcc lattice, the magnetic structure of NiO is perfectly collinear (see for instance in the MAGNDATA database of the Bilbao crystallographic server: http://webbdcrista1.ehu.es/magndata/index.php?this_label=1.6 <http://webbdcrista1.ehu.es/magndata/index.php?this_label=1.6>) , and each triangular plane of spins perpendicular to the <1,1,1>  has NO frustration, as the couplings within the planes are FM . Therefore the small structural structural strain can not be caused to get rid of the frustration.

In general, any magnetic ordering breaks the symmetry of the system, and structural distortions compatible with the new symmetry can happen due to magneto-structural coupling. Often this coupling is too weak to be detected, but in other cases like NiO is strong enough. In the case of NiO the magnetic order reduces the symmetry to monoclinic, and the observed structural distortion corresponds to this symmetry break.

best regards,

Manuel

> El 10/6/2016, a las 0:46, delamora <delamora at unam.mx> escribió:
> 
> No, because in NaCl you do not have magnetic moments that want to find order, so there is no frustration
> In NiO the distortion is a way out of this frustration
> De: Wien <wien-bounces at zeus.theochem.tuwien.ac.at <mailto:wien-bounces at zeus.theochem.tuwien.ac.at>> en nombre de Abderrahmane Reggad <jazairdz at gmail.com <mailto:jazairdz at gmail.com>>
> Enviado: jueves, 9 de junio de 2016 05:26:15 p. m.
> Para: wien at zeus.theochem.tuwien.ac.at <mailto:wien at zeus.theochem.tuwien.ac.at>
> Asunto: Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
>  
> Thanks Dr Delamora for your reply 
> 
> Now I inderstand that and according to this raison "geometrical frustration" , is there any structural distortion in the planes
>  (100) and (110) for the NaCl structure.
> 
> Best regards
> -- 
> Mr: A.Reggad                                           
> Laboratoire de Génie Physique
> Université Ibn Khaldoun - Tiaret
> Algerie
> 
> 
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**************************************************
J. Manuel Perez-Mato
Fac. Ciencia y Tecnologia,
Universidad del Pais Vasco, UPV
48080 BILBAO,
Spain

tel. +34 946012473
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