A new experimental characterization is presented of time-,field-,and temperature-dependent dynamic effects in magnetization of a nanocomposite which displays slow decay.Field and temperature variations of irreversible...A new experimental characterization is presented of time-,field-,and temperature-dependent dynamic effects in magnetization of a nanocomposite which displays slow decay.Field and temperature variations of irreversible susceptibility,χirr,decay coefficient,S,fluctuation field,hf,and activation volume,V,have been calculated for the nanocomposite sample(Co_(80)Ni_(20))using a recently developed modified Preisach–Arrhenius(MPA)model.The sample is composed of non-interacting nanoparticles having negligible reversible magnetization.Non-Arrhenius behavior is observed in both the maximum decay coefficient,Smax,and the fluctuation field,hf,as a function of temperature T.The peak of both temperature curves are identical and occur at a critical temperature Tk of∼50 K,which agrees with our experimental results.Based on the effect of a temperature-dependent chemical potential on energy barrier,hf is studied for T<Tk and T≥Tk,respectively.A more complete MPA model that can predict the magnetization as function of time,field and temperature for a magnetic material with slow decay rates is proposed.This model uses a multi-variable analytical formula,m(ln(t),H,T),which incorporates the characteristic parameters.展开更多
基金supported by National Science Foundation under Contract no.0733526 and no.1031619.
文摘A new experimental characterization is presented of time-,field-,and temperature-dependent dynamic effects in magnetization of a nanocomposite which displays slow decay.Field and temperature variations of irreversible susceptibility,χirr,decay coefficient,S,fluctuation field,hf,and activation volume,V,have been calculated for the nanocomposite sample(Co_(80)Ni_(20))using a recently developed modified Preisach–Arrhenius(MPA)model.The sample is composed of non-interacting nanoparticles having negligible reversible magnetization.Non-Arrhenius behavior is observed in both the maximum decay coefficient,Smax,and the fluctuation field,hf,as a function of temperature T.The peak of both temperature curves are identical and occur at a critical temperature Tk of∼50 K,which agrees with our experimental results.Based on the effect of a temperature-dependent chemical potential on energy barrier,hf is studied for T<Tk and T≥Tk,respectively.A more complete MPA model that can predict the magnetization as function of time,field and temperature for a magnetic material with slow decay rates is proposed.This model uses a multi-variable analytical formula,m(ln(t),H,T),which incorporates the characteristic parameters.
