多晶La_(0.49)Sr_(0.51)MnO_3中的铁磁反共振  

Ferromagnetic antiresonance in polycrystalline La_(0.49)Sr_(0.51)MnO_3

作　　者：舒启清[1,2] 柳文军[1,2] Bhagat S M Lofland S E Troyanchuk I O 

机构地区：[1]深圳大学材料学院 [2]深圳市特种功能材料重点实验室,深圳518060 [3]马里兰大学物理系 [4]白俄罗斯科学院固体物理研究所

出　　处：《深圳大学学报（理工版）》2006年第4期314-319,共6页Journal of Shenzhen University(Science and Engineering)

基　　金：深圳市科技计划资助项目(200604;200606)

摘　　要：采用谐振腔微扰技术测量了多晶La_(0.49)Sr_(0.51)MnO_3的微波吸收(PMA),观察到在居里温度TC或奈尔温度TN附近发生PMA呈现极小值即铁磁反共振(FMAR)现象.基于朗道-利弗希茨-吉尔伯特模型,磁化强度μ0M对温度的依赖关系可以从FMAR得到.发现当外加直流磁场μ0H=0时,不同微波频率下得到的磁化强度μ0M对温度的依赖关系与标度律符合.然而,当μ0H≠0且μ0H<120mT时,不同μ0H下得到的磁化强度μ0M对温度的依赖关系与标度律不符合.在μ0H平行最大微波磁场hrf时,在TC附近随μ0H增加发生FMAR的PMA值增加,且随μ0H增加发生FMAR的温度下降,但此时在TN附近未观测到FMAR.在μ0H垂直hrf时在TC附近随μ0H增加发生FMAR的PMA值减少,且随μ0H增加发生FMAR的温度很少变化,但此时在TN附近发生FMAR的PMA值和温度均几乎不随μ0H变化.这些结果可归因为①多晶La_(0.49)Sr_(0.51)MnO_3是一种由铁磁(FM)和反铁磁(AFM)等多态微区组成的密切合物,是一个包含多个状态和取向互不相同的畴壁的复杂系统;②在μ0H增强或温度下降的过程中,都存在导致PMA增加或减少的两种机制的竞争.The microwave absorption （ PMA ） of the polycrystalline La0.49Sr0.51MnO3 was measured by using a cavity perturbation technique, and the ferromagnetic antiresonance （FMAR） phenomenon near Tc （Curie temperature） or TN （Néel temperature） , i.e. , the minimum of PMA, was observed. Through applying Landau-Lifschitz-Gilbert equation to monodomain ferromagnet, the temperature dependence of magnetizationμ0M was derived from FMAR. It is found that as the applied field μ0H = 0, the temperature dependence of μoM obtained under the different microwave frequencies is in agreement with Scaling Law. However, as μoH ≠0 and μ0H 〈 120 mT, the temperature dependence of μoM obtained under the different μoH is not in agreement with Scaling Law. In the case of μoH parallel to the maximal microwave magnetic field hrf, as μoH increases, the PMA values for FMAR increase at near Tc and the temperatures for FMAR decrease. Meanwhile, there is no FMAR at near TN. In contrast, in the case of μoH perpendicular to hrf, as μoH increases, the PMA values for FMAR decrease at near Tc and the temperatures for FMAR decrease slightly. At near TN both PMA values and the temperatures for FMAR do not change with μoH. These results might be attributed to： ①the polycrystalline La0.49Sr0.51 MnO3 is an intimate mixture of ferromagnetic, antiferromagnetic and charge-ordering microregions and a complex system with many domain boundaries different from each other in the states and orientations; ②when the field μoH increases or the temperature decreases, there always exists a competition between two mechanisms which lead to the increase and the decrease in PMA, respectively.

关 键 词：多晶La0.49Sr0.51MnO3 微波吸收 铁磁反共振 标度律 密切合物 

分 类 号：O513[理学—低温物理]