Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
Thanks again Mr Juan Manuel for the rich information Would you tell me to what extent this information is just: *The character of the unit cell distortion is determined by the orientation of the easy magnetization direction (EMD) of the compounds for binary RCo2 [6]. A close correlation between the EMD and **the symmetry of the distorted Laves phase was observed,* i.e.* a rhombohedral distortion corresponds to the EMD of [1 1 1] of the pseudo-cubic structure, a tetragonal distortion to the EMD of [1 0 0] and an orthorhombic distortion to the EMD of [1 1 0].* *Best regards* -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
Thanks again Pr Staphan for the procedure and the article. Unfortunately I have no idea about the Spin Density Wave and I have to learn more about it. Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
In order to know the symmetry of a structure you do not have to look at the unit cell, but to the symmetry group of the structure. You can have a triclinic structure with a cubic unit cell. Just look at the symmetry group that is indicated in the database, and you will see that its point-group is monoclinic. The monoclinic magnetic structure of NiO in the database comes from an experimental report where any deviation of the positional structure and lattice from the parent cubic was considered negligible. As in general the magnetic induced structural distortions are very weak one has to make a specific effort to detect them and to characterize them experimentally (and I suppose also in calculations as explained by Stefaan Cottenier). A rombohedral strain is just a less general strain than a monoclinic one. If the strain is very weak, a first appoximation to it can be a rombohedral strain, which has only one free parameter to determine, instead of the three that requires the monoclinic strain. best regards, Manuel > El 10/6/2016, a las 12:48, Abderrahmane Reggad escribió: > > > Thanks Mr Khan Manuel for your contribution to enrich the subject of > geometrical frustration and magnetism . > > After reading your contribution, I made the following remarks: > > * you have said:In the case of NiO the magnetic order reduces the symmetry to > monoclinic, but what we know all is that the magnetic order reduces the > symmetry in NiO from cubic to rhombohedral. > > * From theMAGNDATA database, It's mentionned that the magnetic unit cell is > cubic > > Lattice parameters of the magnetic unit cell: > 8.3500 8.3500 8.3500 90. 90. 90. > > Whould you explain that > > Best regards > Mr: A.Reggad > Laboratoire de Génie Physique > Université Ibn Khaldoun - Tiaret > Algerie > > > ___ > Wien mailing list > Wien@zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > SEARCH the MAILING-LIST at: > http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html ** J. Manuel Perez-Mato Fac. Ciencia y Tecnologia, Universidad del Pais Vasco, UPV 48080 BILBAO, Spain tel. +34 946012473 fax. +34 946013500 *** ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
Now , I understand the origins of the tetragonal and the orthorombic distortions for the cubic structure of Chromium Cr. I know how to add the spin-orbit coupling in the wien2k code to get the tertragonal structure , but I don't know how to take the spin-density wave in account . Would you explain to me how to do that We did that long ago: J. Phys.: Condens. Matter 14 (2002) 3275–3283 (http://stacks.iop.org/JPhysCM/14/3275) It boils down to preparing a supercell in which one period of the spin density wave fits (in this case a 1x1x21 supercell), and preparing in case.inst antiferromagnetic moments with a cosine profile as starting situation. In those calculations, the lattice parameters were constrained to (multiples of) the cubic values, as the effect of the spin-density wave on the energy was much larger then the effect of the induced tetragonal symmetry. Stefaan ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
Thanks again Pr Stephan for the rich information Now , I understand the origins of the tetragonal and the orthorombic distortions for the cubic structure of Chromium Cr. I know how to add the spin-orbit coupling in the wien2k code to get the tertragonal structure , but I don't know how to take the spin-density wave in account . Would you explain to me how to do that the little thing will be fruitfull Best regards Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
According to what your are saying , the real magnetic structures for Chromide is tetragonal and orthorhombic and not cubic as it's mentionned in the userguide. I think the cubic magnetic structure fo Cr is given just to simply the calculation for the beginners of the antiferromagnetic calculation. The deviation from cubic symmetry is very, very small, and for most purposes it is perfectly fine to treat Cr as cubic. Moreover, spin-orbit coupling is needed to allow the magnetic moments to break the cubic symmetry to tetragonal. Spin-orbit coupling is a very small effect for a light element as Cr. And in order to get the reduction to orthorhombic symmetry, the spin-density wave in Cr is must be taken into account (its wave vector is transversal to the magnetic moments between 123 K and 311 K, whence the orthorhombic symmetry -- it is parallel to the magnetic moments between 0 K and 123 K, that's why a tetragonal symmetry is possible). When Cr is approximated as an antiferromagnetic crystal without spin-density wave and without spin-orbit coupling, its ground state is exactly cubic. Stefaan ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
Thank you Pr Stefaan Cottenier for your contribution According to what your are saying , the real magnetic structures for Chromide is tetragonal and orthorhombic and not cubic as it's mentionned in the userguide. I think the cubic magnetic structure fo Cr is given just to simply the calculation for the beginners of the antiferromagnetic calculation. Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
Thanks Mr Khan Manuel for your contribution to enrich the subject of geometrical frustration and magnetism . After reading your contribution, I made the following remarks: * you have said:In the case of NiO the magnetic order reduces the symmetry to monoclinic, but what we know all is that the magnetic order reduces the symmetry in NiO from cubic to rhombohedral. * From theMAGNDATA database, It's mentionned that the magnetic unit cell is cubic *Lattice parameters of the magnetic unit cell:* 8.3500 8.3500 8.3500 90. 90. 90. Whould you explain that Best regards Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
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. And this is indeed what happens for bcc Cr (where the initial question was about). Quoting from pages 173-174 of "Phase diagrams of the elements" (David A. Young): "At room pressure and temperature, Cr is bcc. This structure is modified very slightly by two first order magnetic phase transitions. From 0 to 123 K, Cr is antiferromagnetic with a small tetragonal distortion of the bcc lattice. From 123 K to 311 K, Cr is antiferromagnetic with as small orthorhombic distortion of the bcc lattice." The original experiments can be found in http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.23.979 Stefaan -- Stefaan Cottenier Center for Molecular Modeling (CMM) & Department of Materials Science and Engineering (DMSE) Ghent University Tech Lane Ghent Science Park – Campus A building 903 BE-9052 Zwijnaarde Belgium http://molmod.ugent.be http://www.ugent.be/ea/dmse/en email: stefaan.cotten...@ugent.be my conference talks on Youtube: http://goo.gl/P2b1Hs for China: http://i.youku.com/cottenierlectures ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
Thanks again and I have read that the lifting of the Geometrical Frustration lead to Ferrimagnetism. Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
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 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 <mailto:wien-boun...@zeus.theochem.tuwien.ac.at>> en nombre de Abderrahmane > Reggad mailto:jazai...@gmail.com>> > Enviado: jueves, 9 de junio de 2016 05:26:15 p. m. > Para: wien@zeus.theochem.tuwien.ac.at <mailto:wien@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 > > > ___ > Wien mailing list > Wien@zeus.theochem.tuwien.ac.at <mailto:Wien@zeus.theochem.tuwien.ac.at> > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > <http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien> > SEARCH the MAILING-LIST at: > http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html > <http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html> ** J. Manuel Perez-Mato Fac. Ciencia y Tecnologia, Universidad del Pais Vasco, UPV 48080 BILBAO, Spain tel. +34 946012473 fax. +34 946013500 *** ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
I want to say that the distortion does not completely solve the frustration in NiO The geometric frustration in magnetism is vast subject Cheers Pablo de la Mora De: Wien en nombre de Abderrahmane Reggad Enviado: jueves, 9 de junio de 2016 06:10:01 p. m. Para: wien@zeus.theochem.tuwien.ac.at Asunto: Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic Thanks again Dr Delamora for your explanation Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
Thanks again Dr Delamora for your explanation Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
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 en nombre de Abderrahmane Reggad Enviado: jueves, 9 de junio de 2016 05:26:15 p. m. Para: wien@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 G?nie Physique Universit? Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
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 ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Why the antiferromagnetic structure of Cr is still cubic
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" On the other hand, in Cr you have the "Cr up" and "Cr dn" alternated and you can have a clear antiferromagnetic arrangement Pablo De: Wien en nombre de Abderrahmane Reggad Enviado: miércoles, 8 de junio de 2016 05:43 a. m. Para: wien@zeus.theochem.tuwien.ac.at Asunto: [Wien] Why the antiferromagnetic structure of Cr is still cubic Dear wien2k users 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. Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html