The electrical transport and magnetic properties of colossal magnetoresistance material FeCr_(2)S_(4) are studied.The temperature dependence of resistivityρand thermoelectric power S are investigated from 5 to 300 K ...The electrical transport and magnetic properties of colossal magnetoresistance material FeCr_(2)S_(4) are studied.The temperature dependence of resistivityρand thermoelectric power S are investigated from 5 to 300 K and from 77 to 300 K,respectively.The activation energy E ρ obtained from ρ-T is larger than the activation energy ES,obtained from S-T.This indicates that magnetic polarons dominate the conduction behaviour at temperatures above Tc.The M-T curve and electron spin resonance spectra show that the paramagnetic-ferromagnetic transition is incomplete,and that a paramagnetic phase coexists with a ferromagnetic phase in a certain temperature range below Tc.It is proposed that the insulator-metal transition near Tc could be attributed to the gradual delocalizing effect from magnetic polarons to naked carriers.The resistivity in the presented temperature range can be described by considering the coexistence of magnetic polarons and naked carriers.展开更多
The crystal structure of spinel FeCr_(2)S_(4), which shows a semiconductor-metal transition and paramagnetic-ferrimagnetic transition at T_(c)=170 K,was determined by x-ray powder diffraction.It is found that the spin...The crystal structure of spinel FeCr_(2)S_(4), which shows a semiconductor-metal transition and paramagnetic-ferrimagnetic transition at T_(c)=170 K,was determined by x-ray powder diffraction.It is found that the spinel FeCi_(2)S_(4) belongs to a normal spinel structure [Fe^(2+)]_(t)[Cr^(3+)_(2)]_(0)S_(4).The result clearly shows that the spinel FeCr_(2)S_(4) has neither mixed valence of Fe^(3+)and Fe^(2+)ions or Cr^(3+)and Cr^(2+) ions for a double-exchange magnetic interaction, nor a Jahn-Teller cation such as Cr^(3+).The spinels represent a distinct class of colossal magnetoresistance materials,with magnetic ordering driven by superexchange rather than double exchange.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No.19934003the Foundation of Chinese Academy of Sciences,as well as the Research Fund for the Doctoral Program of Higher Education.
文摘The electrical transport and magnetic properties of colossal magnetoresistance material FeCr_(2)S_(4) are studied.The temperature dependence of resistivityρand thermoelectric power S are investigated from 5 to 300 K and from 77 to 300 K,respectively.The activation energy E ρ obtained from ρ-T is larger than the activation energy ES,obtained from S-T.This indicates that magnetic polarons dominate the conduction behaviour at temperatures above Tc.The M-T curve and electron spin resonance spectra show that the paramagnetic-ferromagnetic transition is incomplete,and that a paramagnetic phase coexists with a ferromagnetic phase in a certain temperature range below Tc.It is proposed that the insulator-metal transition near Tc could be attributed to the gradual delocalizing effect from magnetic polarons to naked carriers.The resistivity in the presented temperature range can be described by considering the coexistence of magnetic polarons and naked carriers.
基金Supported in partly by the National Natural Science Foundation under Grant No.KJ951-A1-401,and the National Education Department of China.
文摘The crystal structure of spinel FeCr_(2)S_(4), which shows a semiconductor-metal transition and paramagnetic-ferrimagnetic transition at T_(c)=170 K,was determined by x-ray powder diffraction.It is found that the spinel FeCi_(2)S_(4) belongs to a normal spinel structure [Fe^(2+)]_(t)[Cr^(3+)_(2)]_(0)S_(4).The result clearly shows that the spinel FeCr_(2)S_(4) has neither mixed valence of Fe^(3+)and Fe^(2+)ions or Cr^(3+)and Cr^(2+) ions for a double-exchange magnetic interaction, nor a Jahn-Teller cation such as Cr^(3+).The spinels represent a distinct class of colossal magnetoresistance materials,with magnetic ordering driven by superexchange rather than double exchange.
