Several different models for coercivity are discussed. There are two main situations: i) nanocrystalline magnets, with grain size bellow the single domain particle size, and ii) magnets with grain size above single do...Several different models for coercivity are discussed. There are two main situations: i) nanocrystalline magnets, with grain size bellow the single domain particle size, and ii) magnets with grain size above single domain particle size. The described theories and models are general, and can be applied in either NdFeB magnets, SmFeCoCuZr or strontium ferrite magnets. The spring effect observed in isotropic nanocrystalline magnets can be explained with the Stoner-Wohlfarth model. Modifications of the StonerWohlfarth model are necessary to take into account the effect of interaction between grains. When the grain size is above the single domain size, energy considerations show that nucleation should occur at the surface of grains. Nucleation is interpreted as a two-step process, where domain wall displacement occurs for grain size above single domain size, after a nucleus is first formed. The effect of grain size on the coercive field is discussed.展开更多
Manipulation of antiferromagnetic(AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. Here we report a reversible electrical control of antiferromagnetic moment...Manipulation of antiferromagnetic(AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. Here we report a reversible electrical control of antiferromagnetic moments of FeMn up to 15 nm, using an ionic liquid to exert a substantial electric-field effect. The manipulation is demonstrated by the modulation of exchange spring in[Co/Pt]/FeMn system, where AFM moments in FeMn pin the magnetization rotation of Co/Pt. By carrier injection or extraction,the magnetic anisotropy of the top layer in FeMn is modulated to influence the whole exchange spring and then passes its influence to the [Co/Pt]/FeMn interface, through a distance up to the length of exchange spring that fully screens electric field. Comparing FeMn to IrMn, despite the opposite dependence of exchange bias on gate voltages, the same correlation between carrier density and exchange spring stiffness is demonstrated. Besides the fundamental significance of modulating the spin structures in metallic AFM via all-electrical fashion, the present finding would advance the development of low-power-consumption AFM spintronics.展开更多
基金Project supported by Brazilian Agencies Fundacao de Amparo a Pesquisa do Estado do Rio de Janeiro(FAPERJ)Conselho Nacional de Desenvolvimento Científico e Tecnologico(CNPq)
文摘Several different models for coercivity are discussed. There are two main situations: i) nanocrystalline magnets, with grain size bellow the single domain particle size, and ii) magnets with grain size above single domain particle size. The described theories and models are general, and can be applied in either NdFeB magnets, SmFeCoCuZr or strontium ferrite magnets. The spring effect observed in isotropic nanocrystalline magnets can be explained with the Stoner-Wohlfarth model. Modifications of the StonerWohlfarth model are necessary to take into account the effect of interaction between grains. When the grain size is above the single domain size, energy considerations show that nucleation should occur at the surface of grains. Nucleation is interpreted as a two-step process, where domain wall displacement occurs for grain size above single domain size, after a nucleus is first formed. The effect of grain size on the coercive field is discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.51322101,51231004 and 51571128)the Ministry of Science and Technology of China(Grant No.2014AA032904)
文摘Manipulation of antiferromagnetic(AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. Here we report a reversible electrical control of antiferromagnetic moments of FeMn up to 15 nm, using an ionic liquid to exert a substantial electric-field effect. The manipulation is demonstrated by the modulation of exchange spring in[Co/Pt]/FeMn system, where AFM moments in FeMn pin the magnetization rotation of Co/Pt. By carrier injection or extraction,the magnetic anisotropy of the top layer in FeMn is modulated to influence the whole exchange spring and then passes its influence to the [Co/Pt]/FeMn interface, through a distance up to the length of exchange spring that fully screens electric field. Comparing FeMn to IrMn, despite the opposite dependence of exchange bias on gate voltages, the same correlation between carrier density and exchange spring stiffness is demonstrated. Besides the fundamental significance of modulating the spin structures in metallic AFM via all-electrical fashion, the present finding would advance the development of low-power-consumption AFM spintronics.
