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Comparison of Spin Wave Theory with Neutron Scattering Results for MnF{sub 2}; Comparaison entre la Theorie de l'Onde de Spin et les Resultats Obtenus par la Diffusion des Neutrons dans MnF{sub 2}; Sravnenie teorij spinovoj volny s rezul'tatami rasseyaniya nejtronov dlya MnF{sub 2}; Estudio Comparativo, en el MnF{sub 2}, de la Teoria Ondulatoria del Spin y de los Resultados de la Dispersion Neutronica

Conference:

Abstract

Recent inelastic neutron scattering experiments carried out by Okazaki and Turberfield have provided a direct measure of spin wave dispersion in MnF{sub 2} both at 4.2 Degree-Sign K and at higher temperatures approaching the Neel point. The low temperature results taken together with other magnetic data allow the various exchange constants in MnF{sub 2} to be evaluated with some precision. Using these constants, the spin wave formalism for anti-ferromagnets described by Oguchi has been employed to predict theoretically the temperature dependence of the spin wave dispersion. No disposable parameters are involved and theoretical dispersion curves may be compared with the experimental results for higher temperatures as a test of the spin wave theory. The spin wave energies were evaluated numerically and integrations over the Brillouin zone were carried out, thus avoiding the use of some form of series expansion in temperature. Account was taken of dynamical interactions between pairs of spin waves but kinematical effects were neglected. Renormalization of the spin wave energies was performed. This is an important factor for T/T{sub N}{>=} Vulgar-Fraction-One-Half The agreement between theory and experiment is in fact remarkably good up to temperatures corresponding to about 90% of the Neel point. It would be dangerous  More>>
Authors:
Low, G. G. [1] 
  1. Atomic Energy Research Establishment, Harwell, Berks (United Kingdom)
Publication Date:
Apr 15, 1965
Product Type:
Conference
Report Number:
IAEA-SM-58/38
Resource Relation:
Conference: Symposium on Inelastic Scattering of Neutrons, Bombay (India), 15-19 Dec 1964; Other Information: 7 refs., 1 fig.; Related Information: In: Inelastic Scattering of Neutrons. Vol. I. Proceedings of the Symposium on Inelastic Scattering of Neutrons| 476 p.
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ACCURACY; BRILLOUIN ZONES; COMPARATIVE EVALUATIONS; INELASTIC SCATTERING; MANGANESE FLUORIDES; NEEL TEMPERATURE; NEUTRON DIFFRACTION; RENORMALIZATION; SERIES EXPANSION; SPIN WAVES; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0065-0273 K
OSTI ID:
22141819
Research Organizations:
International Atomic Energy Agency, Vienna (Austria)
Country of Origin:
IAEA
Language:
English
Other Identifying Numbers:
Other: ISSN 0074-1884; TRN: XA13M3385096420
Submitting Site:
INIS
Size:
page(s) 453-459
Announcement Date:
Oct 24, 2013

Conference:

Citation Formats

Low, G. G. Comparison of Spin Wave Theory with Neutron Scattering Results for MnF{sub 2}; Comparaison entre la Theorie de l'Onde de Spin et les Resultats Obtenus par la Diffusion des Neutrons dans MnF{sub 2}; Sravnenie teorij spinovoj volny s rezul'tatami rasseyaniya nejtronov dlya MnF{sub 2}; Estudio Comparativo, en el MnF{sub 2}, de la Teoria Ondulatoria del Spin y de los Resultados de la Dispersion Neutronica. IAEA: N. p., 1965. Web.
Low, G. G. Comparison of Spin Wave Theory with Neutron Scattering Results for MnF{sub 2}; Comparaison entre la Theorie de l'Onde de Spin et les Resultats Obtenus par la Diffusion des Neutrons dans MnF{sub 2}; Sravnenie teorij spinovoj volny s rezul'tatami rasseyaniya nejtronov dlya MnF{sub 2}; Estudio Comparativo, en el MnF{sub 2}, de la Teoria Ondulatoria del Spin y de los Resultados de la Dispersion Neutronica. IAEA.
Low, G. G. 1965. "Comparison of Spin Wave Theory with Neutron Scattering Results for MnF{sub 2}; Comparaison entre la Theorie de l'Onde de Spin et les Resultats Obtenus par la Diffusion des Neutrons dans MnF{sub 2}; Sravnenie teorij spinovoj volny s rezul'tatami rasseyaniya nejtronov dlya MnF{sub 2}; Estudio Comparativo, en el MnF{sub 2}, de la Teoria Ondulatoria del Spin y de los Resultados de la Dispersion Neutronica." IAEA.
@misc{etde_22141819,
title = {Comparison of Spin Wave Theory with Neutron Scattering Results for MnF{sub 2}; Comparaison entre la Theorie de l'Onde de Spin et les Resultats Obtenus par la Diffusion des Neutrons dans MnF{sub 2}; Sravnenie teorij spinovoj volny s rezul'tatami rasseyaniya nejtronov dlya MnF{sub 2}; Estudio Comparativo, en el MnF{sub 2}, de la Teoria Ondulatoria del Spin y de los Resultados de la Dispersion Neutronica}
author = {Low, G. G.}
abstractNote = {Recent inelastic neutron scattering experiments carried out by Okazaki and Turberfield have provided a direct measure of spin wave dispersion in MnF{sub 2} both at 4.2 Degree-Sign K and at higher temperatures approaching the Neel point. The low temperature results taken together with other magnetic data allow the various exchange constants in MnF{sub 2} to be evaluated with some precision. Using these constants, the spin wave formalism for anti-ferromagnets described by Oguchi has been employed to predict theoretically the temperature dependence of the spin wave dispersion. No disposable parameters are involved and theoretical dispersion curves may be compared with the experimental results for higher temperatures as a test of the spin wave theory. The spin wave energies were evaluated numerically and integrations over the Brillouin zone were carried out, thus avoiding the use of some form of series expansion in temperature. Account was taken of dynamical interactions between pairs of spin waves but kinematical effects were neglected. Renormalization of the spin wave energies was performed. This is an important factor for T/T{sub N}{>=} Vulgar-Fraction-One-Half The agreement between theory and experiment is in fact remarkably good up to temperatures corresponding to about 90% of the Neel point. It would be dangerous to extrapolate this result to systems of lower spin as kinematical effects are likely to play a much greater part in such cases. For MnF{sub 2} where S= 5/2 a rough estimate suggests that kinematical effects will not be important until M/M{sub O}-20% and this occurs only within a degree or so of the Neel point. A brief discussion of the likely consequences of a biquadratic exchange term in MnF{sub 2} is given and it is concluded that, if present, such exchange is quite small. (author) [French] Des experiences recentes, executees par Okazaki et Turberfield au moyen de la diffusion inelastique des neutrons, ont fourni une mesure directe de la dispersion de l'onde de spin dans MnF{sub 2}, a 4,2 Degree-Sign K et a des temperatures superieures approchant le point de Neel. Les resultats obtenus a basse temperature, completes par des donnees sur les caracteristiques magnetiques, ont permis d'evaluer les diverses constantes d'echange dans MnF{sub 2} avec une certaine precision. En utilisant ces constantes, l'auteur a employe le formalisme de l'onde de spin pour substances antiferromagnetiques, decrit par Oguchi, pour prevoir theoriquement comment varie la dispersion de l'onde de spin en fonction de la temperature. Aucun des parametres mis enjeu n'est superflu, et les courbes theoriques de dispersion peuvent etre comparees aux resultats experimentaux pour des temperatures plus elevees en vue de verifier la theorie de l'onde de spin. L'auteur a evalue numeriquement les energies d'onde de spin et integre sur la zone de Brillouin, evitant ainsi tout developpement en serie selon la temperature. Ils a tenu compte des interactions dynamiques entre paires d'ondes de spin, mais il a neglige les effets cinematiques. Les energies d'onde de spin ont fait l'objet d'une renormalisation. C'est la un facteur important pour T/T{sub N} Greater-Than-Or-Equal-To Vulgar-Fraction-One-Half . La concordance entre la theorie et les resultats experimentaux demeure, en fait, remarquable jusqu'a des temperatures correspondant a environ 90% du point de NeeL II serait dangereux d'extrapoler ces resultats en vue de les utiliser pour des systemes a spin plus faible, car les effets cinematiques joueraient probablement un role beaucoup plus important dans ces cas. En ce qui concerne MnF{sub 2}, ou S= 5/2, une evaluation grossiere laisse supposer que les effets cinematiques seront peu importants jusqu'a M/M{sub O}-20%, ce qui ne se produit que dans les limites d'un degre environ du point de Neel, L'auteur discute brievement les consequences que peut avoir un terme d'echange biquadratique dans MnF{sub 2}; il conclut que, si cet echange existe, il est tres faible. (author) [Spanish] Los experimentos de dispersion inelastica de neutrones, realizados recientemente por Okazaki y Tuberfield, han proporcionado un medio de medir directamente la dispersion de las ondas de spin en el MnF{sub 2}, tanto a 4,2 Degree-Sign K como a temperaturas mas elevadas proximas al punto de NeeL Los resultados obtenidos a bajas temperaturas, considerados conjuntamente con otros datos magneticos, permiten evaluar con cierta precision las diversas constantes de intercambio en el MnF{sub 2}. Haciendo uso de estas constantes, se ha empleado el formalismo de las ondas de spin para sustancias antiferromagneticas descrito por Oguchi para predecir teoricamente la dispersion de las ondas de spin en funcion de la temperatura. No intervienen parametros redundantes y las curvas de dispersion teoricas pueden compararse con los resultados experimentales obtenidos a temperaturas mas elevadas, como prueba de la teoria ondulatoria del spin. Se han evaluado numericamente las energias de las ondas de spin y se han realizado integraciones que abarcan la zona de Brillouin, por lo que no es preciso emplear alguna forma de desarrollo en serie en funcion de la temperatura. Se tuvieron en cuenta las interacciones dinamicas entre pares de ondas de spin, pero se despreciaron los efectos cinematicos. Se procedio a renormalizar las energias de las ondas de spin. Esto constituye un importante factor en el caso de T/T{sub N} Greater-Than-Or-Equal-To Vulgar-Fraction-One-Half . La concordancia entre los datos teoricos y los resultados experimentales es, de hecho, notable hasta temperaturas correspondientes a un 90% aproximadamente del punto de Neel. Extrapolar este resultado a sistemas de spin mas bajo seria arriesgado, ya que en esos casos es probable que los efectos cinematicos desempenen un papel mucho mas importante. Para el MnF{sub 2}, en el que S= 5/2, un calculo aproximado sugiere que los efectos cinematicos no tendran importancia hasta llegar a un valor de M/M{sub O}-20%, y esto ocurre unicamente a menos de un grado, aproximadamente, del punto de Neel. Et autor describe sucintamente las probables consecuencias de un termino bicuadratico de intercambio en el MnF{sub 2}, y llega a la conclusion de que tal intercambio, de producirse, es muy pequeno. (author) [Russian] V rezul'tate jeksperimentov po neuprugomu rassejaniju, kotorye proveli nedavno Okazaki i Turberfil'd, poluchena prjamaja mera dispersii spinovoj volny v MnF{sub 2} i pri 4,2 Degree-Sign K i pri bolee vysokih temperaturah, priblizhajushhihsja k tochke Nila. Nizkotemperaturnye rezul'taty vmeste s drugimi magnitnymi svojstvami pozvoljajut ocenit' s nekotoroj tochnost'ju razlichnye obmennye konstanty v MnF{sub 2}. Ispol'zuja jeti konstanty, byl primenen opisannyj Oguchi formalizm teorii spinovoj volny dlja antiferromagnetikov v celjah teoreticheskogo predskazanija zavisimosti dispersii spinovoj volny ot temperatury. Ni odin iz imejushhihsja parametrov ne zatragivaetsja, i teoreticheskie krivye dispersii mozhno sravnit' s jeksperimental'nymi rezul'tatami v otnoshenii bolee vysokih temperatur v kachestve proverki teorii spinovoj volny. Byli prinjaty v raschet chislennye znachenija jenergii spinovyh voln i byli vzjaty integral' po zone Brilljujena, i tem samym udalos' izbezhat' ispol'zovanija nekotoroj formy razlozhenija v rjad po temperature. Uchteny dinamicheskie vzaimodejstvija mezhdu parami spinovyh voln, odnako kinematicheskie jeffekty ne prinimalis' vo vnimanie. Byla proizvedena perenormirovka jenergij spinovyh voln. Jeto-vazhnyj faktor dlja T/T{sub N} Greater-Than-Or-Equal-To Vulgar-Fraction-One-Half . Fakticheski teoreticheskie i jeksperimental'nye dannye v znachitel'noj stepeni sovpadajut pri temperaturah, sootvetstvujushhih priblizitel'no 90% tochki Nila. Opasno jekstrapolirovat' jetot rezul'tat k sistemam s men'shimi spinami, poskol'ku, verojatno, kinematicheskie jeffekty igrajut znachitel'no bol'shuju rol' v takih sluchajah. Dlja MnF{sub 2}, gde S = 5/2, soglasno priblizitel'noj ocenke, kinematicheskie jeffekty ne igrajut sushhestvennoj roli do M/M{sub O} Tilde-Operator 20%, chto proishodit tol'ko na rasstojanii primerno odnogo gradusa ot tochki Nila. Kratko obsuzhdajutsja verojatnye posledstvija bikvadratnogo chlena obmena v MnF2 i delaetsja vyvod o tom, chto takoj obmen, esli on prisutstvuet, javljaetsja dovol'no neznachitel'nym. (author)}
place = {IAEA}
year = {1965}
month = {Apr}
}