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1、SpinmodelswithrandomanisotropyandreflectionsymmetryPasqualeCalabrese,1,2AndreaPelissetto,3EttoreVicari41ScuolaNormaleSuperioreandINFN,PiazzadeiCavalieri7,I-56126Pisa,Italy.2TheoreticalPhysics,UniversityofOxford,1KebleRoad,OxfordOX13NP,UnitedKingdom.3DipartimentodiFisic
2、adell’Universit`adiRomaIandINFN,I-00185Roma,Italy.4DipartimentodiFisicadell’Universit`aandINFN,ViaBuonarroti2,I-56127Pisa,Italy.e-mail:calabres@df.unipi.it,Andrea.Pelissetto@roma1.infn.it,vicari@df.unipi.it.(February2,2008)AbstractWestudythecriticalbehaviorofageneralc
3、lassofcubic-symmetricspinsystemsinwhichdisorderpreservesthereflectionsymmetrysa→−sa,sb→sbforb6=a.Thisincludesspinmodelsinthepresenceofrandomcubic-symmetricanisotropywithprobabilitydistributionvanishingoutsidethelatticeaxes.Usingnonperturbativeargumentsweshowtheexistenc
4、eofastablefixedpointcorrespondingtotherandom-exchangeIsinguniversalityclass.Thefield-theoreticalrenormalization-groupflowisinvestigatedintheframeworkofafixed-dimensionexpansioninpowersofappropriatequarticcouplings,computingthecorrespondingβ-functionstofiveloops.Thisanal-ys
5、isshowsthattherandomIsingfixedpointistheonlystablefixedpointthatisaccessiblefromtherelevantparameterregion.Therefore,ifthesys-temundergoesacontinuoustransition,itbelongstotherandom-exchangeIsinguniversalityclass.Theapproachtotheasymptoticcriticalbehavioriscontrolledbysc
6、alingcorrectionswithexponent∆=−αr,whereαr≃−0.05isthespecific-heatexponentoftherandom-exchangeIsingmodel.PACSNumbers:75.10.Nr,75.10.Hk,64.60.AkarXiv:cond-mat/0311576v1[cond-mat.stat-mech]25Nov2003TypesetusingREVTEX1I.INTRODUCTIONANDSUMMARYThecriticalbehaviorofmagneticsy
7、stemsinthepresenceofquencheddisorderhasbeenthesubjectofextensivetheoreticalandexperimentalstudy.Animportantclassofsystemsisformedbyamorphousalloysofrareearthswithasphericalelectrondistributionandtransi-tionmetals,forinstanceTbFe2andYFe2.Thesesystemsaremodeled[1,2]byth
8、eHeisenbergmodelwithrandomuniaxialsingle-siteanisotropy,or,inshort,bytherandom-anisotropymodel(RAM)XX2HRAM=−J~sx·~sy−D0(~ux·
