In this work, we experimentally investigated the thermal stability of the interlayer exchange coupling field(Hex) and strength(-Jiec) in synthetic antiferromagnetic(SAF) structure of [Pt(0.6)/Co(0.6)]2/Ru(tRu)/[Co(0.6...In this work, we experimentally investigated the thermal stability of the interlayer exchange coupling field(Hex) and strength(-Jiec) in synthetic antiferromagnetic(SAF) structure of [Pt(0.6)/Co(0.6)]2/Ru(tRu)/[Co(0.6)/Pt(0.6)]4multilayers with perpendicular anisotropy. Depending on the thickness of the spacing ruthenium(Ru) layer, the observed interlayer exchange coupling can be either ferromagnetic or antiferromagnetic. The Hexwere studied by measuring the magnetization hysteresis loops in the temperature range from 100 K to 700 K as well as the theoretical calculation of the-Jiec. It is found that the interlayer coupling in the multilayers is very sensitive to the thickness of Ru and temperature. The Hexexhibits either a linear or a non-linear dependence on the temperature for different thickness of Ru. Furthermore, our SAF multilayers show a high thermal stability even up to 600 K(Hex= 3.19 kOe,-Jiec= 1.97 erg/cm~2 for tRu=0.6 nm, the unit 1 Oe = 79.5775 A·m-1), which was higher than the previous studies.展开更多
The antiferromagnetic(AFM) interlayer coupling effective field in a ferromagnetic/non-magnetic/ferromagnetic(FM/NM/FM) sandwich structure, as a driving force, can dramatically enhance the ferromagnetic resonance(FMR) ...The antiferromagnetic(AFM) interlayer coupling effective field in a ferromagnetic/non-magnetic/ferromagnetic(FM/NM/FM) sandwich structure, as a driving force, can dramatically enhance the ferromagnetic resonance(FMR) frequency. Changing the non-magnetic spacer thickness is an effective way to control the interlayer coupling type and intensity, as well as the FMR frequency. In this study, Fe Co B/Ru/Fe Co B sandwich trilayers with Ru thickness(tRu) ranging from 1 A to 16 A are prepared by a compositional gradient sputtering(CGS) method. It is revealed that a stress-induced anisotropy is present in the Fe Co B films due to the B composition gradient in the samples. A tRu-dependent oscillation of interlayer coupling from FM to AFM with two periods is observed. An AFM coupling occurs in a range of 2 A ≤ tRu≤ 8 A and over 16 A, while an FM coupling is present in a range of tRu< 2 A and 9 A ≤ tRu≤ 14.5 A. It is interesting that an ultrahigh optical mode(OM) FMR frequency in excess of 20 GHz is obtained in the sample with tRu= 2.5 A under an AFM coupling. The dynamic coupling mechanism in trilayers is simulated, and the corresponding coupling types at different values of tRuare verified by Layadi’s rigid model. This study provides a controllable way to prepare and investigate the ultrahigh FMR films.展开更多
A series of (Sm, Tb)FeCo/Cr/TbFeCo trilayers with perpendicular anisotropy was prepared by RF magnetron sputtering, and the effect of Cr interlayer thickness on magnetic properties and interlayer exchange coupling w...A series of (Sm, Tb)FeCo/Cr/TbFeCo trilayers with perpendicular anisotropy was prepared by RF magnetron sputtering, and the effect of Cr interlayer thickness on magnetic properties and interlayer exchange coupling was investigated. All the samples showed strong out-of-plane anisotropy but their hysteresis loops displayed two types : singlephase and double-phase, indicating that interlayer exchange coupling and magnetic properties varied with the thickness of Cr interlayer. Both saturation field Hs and (1-Mr/Ms) curves indicated that interlayer exchange coupling oscillated between antiferromagnetic and ferromagnetic with a period of 1.6 nm, and the oscillation strength attenuated with increasing Cr interlayer thickness. After being annealed at 450℃ for 25 min, the hysteresis loops of all the samples became single-phase type and coercivity Hc decreased greatly, which could be attributed to the decrease of effective anisotropy in (Sm, TbFeCo) grains.展开更多
A numerical study reports that the zero-field skyrmions in Fe Ge thin films are stabilized when a Fe Ge layer is exchange coupled to a single-domain Ni layer,which has been magnetized perpendicularly.Due to the small ...A numerical study reports that the zero-field skyrmions in Fe Ge thin films are stabilized when a Fe Ge layer is exchange coupled to a single-domain Ni layer,which has been magnetized perpendicularly.Due to the small thickness,an easy-plane anisotropy in the Fe Ge layer is taken into account,and the skyrmion-crystal state is favored to appear for low anisotropies and intermediate Fe Ge/Ni interlayer exchange couplings,and finally transformed from a labyrinth-like and into an out-ofplane uniform state for the large couplings or into an in-plane state for the high anisotropies.Furthermore,the maximum skyrmion charge number is bigger for the periodic and fixed boundary conditions with an out-of-plane magnetization;on the contrary,the Bloch-type skyrmions can be frozen and stabilized for the larger couplings on the fixed boundary with an in-plane magnetization,similar to the experimental results of the magnetic-field-induced skyrmions.Finally,the skyrmion charge number and diameter both decrease if the nonmagnetic defects exist,and the skyrmion centers are prone to being captured by defect sites.This work evidences that the ensembles of homochiral skyrmions stabilized in the multilayers fabricated by well-established technologies present a roadmap to design new classes of the materials that can host skyrmions.展开更多
The magnon energy band in a four-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green's function technique. It is found that three modulated energy gaps exist in the magnon ene...The magnon energy band in a four-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green's function technique. It is found that three modulated energy gaps exist in the magnon energy band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the three energy gaps. The magnon energy gaps of the four-layer ferromagnetic superlattice are different from those of the three-layer one. For the four-layer ferromagnetic superlattice, the disappearance of the magnon energy gaps △ω12, △ω23 and △ω34 all correlates with the symmetry of this system. The zero energy gap △ω23 correlates with the symmetry of interlayer exchange couplings, while the vanishing of the magnon energy gaps △ω12 and △ω34 corresponds to a translational symmetry of x-direction in the lattice. When the parameters of the system deviate from these symmetries, the three energy gaps will increase.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11704191)the Jiangsu Specially-Appointed Professor,the Natural Science Foundation of Jiangsu Province of China(Grant No.BK20171026)the Six-Talent Peaks Project in Jiangsu Province,China(Grant No.XYDXX-038)
文摘In this work, we experimentally investigated the thermal stability of the interlayer exchange coupling field(Hex) and strength(-Jiec) in synthetic antiferromagnetic(SAF) structure of [Pt(0.6)/Co(0.6)]2/Ru(tRu)/[Co(0.6)/Pt(0.6)]4multilayers with perpendicular anisotropy. Depending on the thickness of the spacing ruthenium(Ru) layer, the observed interlayer exchange coupling can be either ferromagnetic or antiferromagnetic. The Hexwere studied by measuring the magnetization hysteresis loops in the temperature range from 100 K to 700 K as well as the theoretical calculation of the-Jiec. It is found that the interlayer coupling in the multilayers is very sensitive to the thickness of Ru and temperature. The Hexexhibits either a linear or a non-linear dependence on the temperature for different thickness of Ru. Furthermore, our SAF multilayers show a high thermal stability even up to 600 K(Hex= 3.19 kOe,-Jiec= 1.97 erg/cm~2 for tRu=0.6 nm, the unit 1 Oe = 79.5775 A·m-1), which was higher than the previous studies.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51871127 and 11674187)。
文摘The antiferromagnetic(AFM) interlayer coupling effective field in a ferromagnetic/non-magnetic/ferromagnetic(FM/NM/FM) sandwich structure, as a driving force, can dramatically enhance the ferromagnetic resonance(FMR) frequency. Changing the non-magnetic spacer thickness is an effective way to control the interlayer coupling type and intensity, as well as the FMR frequency. In this study, Fe Co B/Ru/Fe Co B sandwich trilayers with Ru thickness(tRu) ranging from 1 A to 16 A are prepared by a compositional gradient sputtering(CGS) method. It is revealed that a stress-induced anisotropy is present in the Fe Co B films due to the B composition gradient in the samples. A tRu-dependent oscillation of interlayer coupling from FM to AFM with two periods is observed. An AFM coupling occurs in a range of 2 A ≤ tRu≤ 8 A and over 16 A, while an FM coupling is present in a range of tRu< 2 A and 9 A ≤ tRu≤ 14.5 A. It is interesting that an ultrahigh optical mode(OM) FMR frequency in excess of 20 GHz is obtained in the sample with tRu= 2.5 A under an AFM coupling. The dynamic coupling mechanism in trilayers is simulated, and the corresponding coupling types at different values of tRuare verified by Layadi’s rigid model. This study provides a controllable way to prepare and investigate the ultrahigh FMR films.
基金Project supported by the National Natural Science Foundation of China (90306008) Item of"Engineering Research Insti-tute ,Peking University (ERIPKU)",and Spaceflight Science and Technology Innovation Foundation
文摘A series of (Sm, Tb)FeCo/Cr/TbFeCo trilayers with perpendicular anisotropy was prepared by RF magnetron sputtering, and the effect of Cr interlayer thickness on magnetic properties and interlayer exchange coupling was investigated. All the samples showed strong out-of-plane anisotropy but their hysteresis loops displayed two types : singlephase and double-phase, indicating that interlayer exchange coupling and magnetic properties varied with the thickness of Cr interlayer. Both saturation field Hs and (1-Mr/Ms) curves indicated that interlayer exchange coupling oscillated between antiferromagnetic and ferromagnetic with a period of 1.6 nm, and the oscillation strength attenuated with increasing Cr interlayer thickness. After being annealed at 450℃ for 25 min, the hysteresis loops of all the samples became single-phase type and coercivity Hc decreased greatly, which could be attributed to the decrease of effective anisotropy in (Sm, TbFeCo) grains.
基金the National Natural Science Foundation of China(Grant No.11774045)the Joint Research Fund Liaoning-Shenyang National Laboratory for Materials Science(Grant No.20180510008)the Fundamental Research Funds for Central Universities,China(Grant No.N182410008-1)。
文摘A numerical study reports that the zero-field skyrmions in Fe Ge thin films are stabilized when a Fe Ge layer is exchange coupled to a single-domain Ni layer,which has been magnetized perpendicularly.Due to the small thickness,an easy-plane anisotropy in the Fe Ge layer is taken into account,and the skyrmion-crystal state is favored to appear for low anisotropies and intermediate Fe Ge/Ni interlayer exchange couplings,and finally transformed from a labyrinth-like and into an out-ofplane uniform state for the large couplings or into an in-plane state for the high anisotropies.Furthermore,the maximum skyrmion charge number is bigger for the periodic and fixed boundary conditions with an out-of-plane magnetization;on the contrary,the Bloch-type skyrmions can be frozen and stabilized for the larger couplings on the fixed boundary with an in-plane magnetization,similar to the experimental results of the magnetic-field-induced skyrmions.Finally,the skyrmion charge number and diameter both decrease if the nonmagnetic defects exist,and the skyrmion centers are prone to being captured by defect sites.This work evidences that the ensembles of homochiral skyrmions stabilized in the multilayers fabricated by well-established technologies present a roadmap to design new classes of the materials that can host skyrmions.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 50331030, 10674139 and 10274087)the Natural Science Foundation of Liaoning Province, China (Grant No 20062040)
文摘The magnon energy band in a four-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green's function technique. It is found that three modulated energy gaps exist in the magnon energy band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the three energy gaps. The magnon energy gaps of the four-layer ferromagnetic superlattice are different from those of the three-layer one. For the four-layer ferromagnetic superlattice, the disappearance of the magnon energy gaps △ω12, △ω23 and △ω34 all correlates with the symmetry of this system. The zero energy gap △ω23 correlates with the symmetry of interlayer exchange couplings, while the vanishing of the magnon energy gaps △ω12 and △ω34 corresponds to a translational symmetry of x-direction in the lattice. When the parameters of the system deviate from these symmetries, the three energy gaps will increase.