共查询到20条相似文献,搜索用时 15 毫秒
1.
Positive exchange bias field (He) is observed in Tb/Cr (tCr)/FeCo trilayers at 5 K without cooling field, and negative He for Tb/FeCo bilayer. The negative He of Tb/FeCo implies the FM coupling at the interface due to Co and Fe dominate in the magnetization of the ferrimagnetic interlayer alloy of FeCo and Tb. With the inserting of Cr layer, this situation is broken, and the positive He implies the antiferromagnetic interlayer coupling. A peak of He = 6.0 mT for trilayers with tCr = 1.5 nm is corresponding to the minimum value of coercivity as a function of tCr at 5 K, which is used to study the effect of the cooling field (Hfc) on He as a function of temperature. It is found that Hfc of 100 mT triggers He from positive to negative at T ≤ 15 K. The magnetoresistance results also confirm the coexistence of multiple MR mechanisms in these trilayers. 相似文献
2.
We consider the models of ferromagnetic (FM)/antiferromagnetic (AFM) bilayers and trilayers and perform a modified Monte Carlo method to study their exchange bias (EB) properties at low temperature after field cooling on increasing one component thickness at the expense of the other one. The results indicate that EB is insensitive to the thickness variations as the FM layer is thicker than the AFM one. Otherwise, it has a steep increase with the decrease of FM thickness, but the purely inverse proportion is no longer valid due to the dual influences of FM and AFM thicknesses. EB in trilayers should be approximately twice larger than that in bilayers because there is a double interfacial area in the trilayers compared with the bilayers, but the dispersed FM/AFM distributions may break this relation as a result of thermal destabilization. Moreover, EB is independent of FM/AFM stacking sequences probably because of the ideal interface between them. It has been clarified unambiguously that such control of EB through varying the FM/AFM dimensions in heterostructures is attractive for spintronics applications. 相似文献
3.
R. R. Gareev D. E. Bü rgler M. Buchmeier R. Schreiber P. Grü nberg 《Journal of magnetism and magnetic materials》2002,240(1-3):235-237
Fe/Fe1−xSix/Fe (x=0.4–1.0) wedge-type epitaxial trilayers with improved homogeneity are grown by co-evaporation from two electron-beam sources. The coupling strengths of the bilinear (J1) and biquadratic (J2) coupling terms are derived from Brillouin light scattering (BLS) spectra and longitudinal MOKE hysteresis loops. The total coupling strength J=J1+J2 increases dramatically with increasing x and reaches values in excess of 6 mJ/m2. 相似文献
4.
V.P. Nascimento E.C. Passamani A.D. Alvarenga F. Pelegrini A. Biondo E. Baggio Saitovitch 《Journal of magnetism and magnetic materials》2008,320(14):e272-e274
We have studied the effect of roughness on the exchanged biased NiFe/FeMn/NiFe trilayers system. The samples were prepared under three different argon working pressures (2, 5 and 10 mTorr) to obtain different roughness degrees. The root mean square roughness of the NiFe/FeMn interfaces enhances as the argon working pressure during the deposition increases from 2 to 10 mTorr. High-angle X-ray diffraction reveals that the samples have 1 1 1 texture and besides, possible changes in grain size could be an extra contribution to the interfacial roughness. Magnetometry measurements have shown that the coervive field enhances as the root mean square roughness of the NiFe/FeMn interfaces increases, while the dependence of the exchange bias field runs in the opposite way. 相似文献
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Demokritov SO Bayer C Poppe S Rickart M Fassbender J Hillebrands B Kholin DI Kreines NM Liedke OM 《Physical review letters》2003,90(9):097201
The manipulation of the antiferromagnetic interlayer coupling in epitaxial Fe/Cr/Fe(001) trilayers by 5 keV He ion beam irradiation has been investigated. It is shown that even for irradiation with low fluences a drastic change in strength of the coupling appears. For thin Cr spacers (below 0.6-0.7 nm) it decreases with fluence, becoming ferromagnetic for fluences above 2x10(14) ions/cm(2). The effect is connected with the creation of magnetic bridges in the layered system due to atomic exchange events caused by the bombardment. For thicker Cr spacers an enhancement of the antiferromagnetic coupling strength is found. A possible explanation of the enhancement effect is given. 相似文献
7.
Training effects in a new class of exchange biased ferromagnet/antiferromagnet/ferromagnet trilayers (Co/NiO/[Co/Pt]3) with mutually orthogonal easy axes have been measured and successfully modeled. Previous experiments have demonstrated an enhanced blocking temperature as well as the ability to isothermally field tune the magnitude of the room temperature in-plane exchange bias. These effects have been attributed to the presence of the [Co/Pt] multilayer with perpendicular magnetic anisotropy, which variably pins the backside NiO domains. Here we show that the tuning of the exchange bias and the blocking temperature enhancement are highly dependent on both the temperature and the in-plane remanence of the normally out-of-plane [Co/Pt] multilayer, achieved using modest in-plane set fields. Training effects and their dependence on temperature and in-plane remanence are modeled using a thermodynamic approach. The in-plane remanence of the [Co/Pt] acts only to set the equilibrium exchange bias value and sets the scale for the blocking temperature; it has no effect on the training. We conclude that training effects occur only at the Co/NiO interface and that the relaxation towards equilibrium is confined to this interface. The field enhanced blocking temperature and isothermal tuning of exchange bias in these magnetic heterostructures with mutually orthogonal easy axes could play a role in the enhancement of exchange bias effects in future spin-valve devices. A thorough knowledge of the training effects is essential to account for the fundamental relaxation mechanisms that occur with repeated field cycling. 相似文献
8.
The exchange-bias (EB) properties of Mg-diluted Ni1−xMgxO/Ni (0?x?0.3) granular systems have been investigated. Magnetic dilution with Mg greatly affects the EB field and the coercivity. The temperature dependence of the EB field and the coercivity can be explained in terms of formation of domain states. The value of the EB field increases and shows a maximum value with increasing cooling field, which can be explained by the competition between the field-dependent Zeeman energy and the exchange interaction at the interface. 相似文献
9.
Ultrathin epitaxial Fe films on Cu(1 0 0) with perpendicular magnetization have been used as templates for the preparation of FCC Fe/Cu/Fe trilayers. The magnetic anisotropy and the coupling of these films have been studied by in-situ magneto optical Kerr effect measurements and Kerr microscopy. The magnetic coupling of both Fe layers is found to be dominated by magnetostatic interaction. Adsorbate-induced spin reorientation in the top layer also causes spin reorientation in the bottom layer. The governing role of the Fe-vacuum interface for the magnetism of the whole trilayer is demonstrated. 相似文献
10.
The magnetic properties of Fe/Zn/Fe trilayers have been studied by ferromagnetic resonance and magnetization measurements. These measurements have been used to investigate the magnetic anisotropy of the iron layers and the magnetic coupling across the semiconductor spacer. The angular dependence of the resonance spectra has been measured in-plane and out-of-plane in order to deduce magnetic anisotropy constants of the samples. Experimental data were fitted by using an energy-density expression that includes bulk cubic anisotropy, growth-induced uniaxial in-plane anisotropy and perpendicular-surface anisotropy terms. A small ferromagnetic coupling is observed in the trilayers with spacer thickness up to
. 相似文献
11.
Xiao-Yong Xu 《Surface science》2009,603(5):814-818
By investigating the antiferromagnetic spin configuration, the exchange anisotropy and the interfacial spin-flop coupling in ferromagnetic/antiferromagnetic (FM/AF) bilayers have been discussed in detail. The results show that there are four possible cases for the AF spins, namely the reversible recovering case, irreversible half-rotating case, irreversible reversing and irreversible half-reversing cases. Moreover, the realization of the cases strongly depends on interface quadratic coupling, interface spin-flop (biquadratic) coupling and AF thickness. The magnetic phase diagram in terms of the AF thickness tAF, the interfacial bilinear coupling J1 and the spin-flop coupling J2 has been constructed. The corresponding critical parameters in which the exchange bias will occur or approach saturation have been also presented. Specially, the small spin-flop exchange coupling may result in an exchange bias without the interfacial bilinear exchange coupling. However, in general, the spin-flop exchange coupling can weaken or eliminate the exchange bias, but always enhances the coercivity greatly. 相似文献
12.
R.K. Das 《Journal of magnetism and magnetic materials》2010,322(17):2618-2621
The magnetic properties of thin-film Pd/Fe/Pd trilayers in which an embedded - thick ultrathin layer of Fe induces ferromagnetism in the surrounding Pd have been investigated. The thickness of the ferromagnetic trilayer is controlled by varying the thickness of the top Pd layer over a range from 8 to . As the thickness of the top Pd layer decreases, or equivalently as the embedded Fe layer moves closer to the top surface, the saturated magnetization normalized to area and the Curie temperature decreases, whereas the coercivity increases. These thickness-dependent observations for proximity-polarized thin-film Pd are qualitatively consistent with finite size effects that are well known for regular thin-film ferromagnets. The critical exponent β of the order parameter (magnetization) is found to approach the mean field value of 0.5 as the thickness of the top Pd layer increases. The functional forms for the thickness dependences, which are strongly modified by the nonuniform exchange interaction in the polarized Pd, provide important new insights to understand nanomagnetism in two-dimensions. 相似文献
13.
Epitaxial superlattices of ferromagnetic/paramagnetic La0.67Sr0.33MnO3/SrIrO3 materials have been prepared on SrTiO3 (100) substrate using pulse laser deposition technique. An unexpected onset of interface magnetic interaction has been observed around 40 K. Interestingly, magnetic exchange bias effect has been observed in both field cooled and zero field cooled magnetization loops, however, the shifting of loop is opposite in both measurements. Exchange bias field vanishes as temperature increases to interface magnetic ordering temperature. Moreover, exchange bias field is found to decrease with increasing cooling field. We believe that tuning of magnetic exchange at interface during field cooling induces this evolution in nature of exchange bias field. 相似文献
14.
Zero-field-cooled (ZFC) and field-cooled (FC) hysteresis loops of egg- and ellipsoid-shaped nanoparticles with inverted ferromagnetic (FM)-antiferromagnetic (AFM) core-shell morphologies are simulated using a modified Monte Carlo method, which takes into account both the thermal fluctuations and energy barriers during the rotation of spin. Pronounced exchange bias (EB) fields and reduced coercivities are obtained in the FC hysteresis loops. The analysis of the microscopic spin configurations allows us to conclude that the magnetization reversal occurs by means of the nucleation process during both the ZFC and FC hysteresis branches. The nucleation takes place in the form of “sparks” resulting from the energy competition and the morphology of the nanoparticle. The appearance of EB in the FC hysteresis loops is only dependent on that the movements of “sparks” driven by magnetic field at both branches of hysteresis loops are not along the same axis, which is independent of the strength of AFM anisotropy. The tilt of “spark” movement with respect to the symmetric axis implies the existence of additional unidirectional anisotropy at the AFM/FM interfaces as a consequence of the surplus magnetization in the AFM core, which is the commonly accepted origin of EB. Our simulations allow us to clarify the microscopic mechanisms of the observed EB behavior, not accessible in experiments. 相似文献
15.
The structure dependence of exchange bias in ferromagnetic/antiferromagnetic (FM/AF) bilayers has been investigated in detail by extending Slonczewski's 'proximity magnetism' idea. Here three important parameters are discussed for FM/AF bilayers, i.e. interracial bilinear exchange coupling J1, interracial biquadratic (spin-flop) exchange coupling J2 and antiferromagnetic layer thickness tAF. The results show that both the occurrence and the variety of the exchange bias strongly depend on the above parameters. More importantly, the small spin-flop exchange coupling may result in an exchange bias without the interracial bilinear exchange coupling. However, in general, the spin-flop exchange coupling cannot result in the exchange bias. The corresponding critical parameters in which the exchange bias will occur or approach saturation are also presented. 相似文献
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For the ferromagnetic (FM)/antiferromagnetic (AFM) bilayers, both negative and positive exchange bias HE have been observed for low and high cooling field HCF, respectively. The thickness dependence of HE and coercivity HC have been investigated for the cases of negative and positive HE. It is found that the negative HE and the positive one have similar FM thickness dependence that is attributed to the interfacial nature of exchange bias. However, the AFM thickness dependence of positive HE is completely contrary to that of the negative one, which clearly demonstrates that the AFM spins play different roles for the cases of positive and negative HE. In particular, the AFM thickness of positive HE was first highlighted by an AFM spin canting model. These results should be attributed to the interfacial spin configuration after field cooling procedure. 相似文献
18.
The dynamics of magnetic vortices in double disks coupled with a bridge are studied by micromagnetic simulations. There are three types of magnetic configurations being found, which depend on the size of the bridge and the chiralities of the vortices. The exchange coupling between the vortices, which is mediated by the magnetizations in the bridge, influences the trajectories and oscillation frequencies of the vortices. Moreover, the frequency depends on the configurations of the double disks and the bridge size. 相似文献
19.
A new method was developed to control Co film oxidation in an epitaxially grown Cu(wedge)/Co/Cu(0 0 1) film. By annealing the film at 200 °C within 10−6 Torr oxygen environment, we find that the top Cu wedge controls the Co underlayer oxidation continuously as a function of the Cu film thickness. Magneto-Optic Kerr Effect measurement shows that the exchange bias of the resulting CoO/Co film exhibits a systematic variation with the Cu thickness, thus offering a new method of tailoring the exchange bias of CoO/Co films. 相似文献
20.
胡耀乔 《原子与分子物理学报》2014,31(6)
采用基于密度泛函理论(DFT)的第一性原理计算方法,在现有的单分子磁体交换耦合常数计算方法的基础上提出了一种新的计算方法.采用新方法计算两个原子之间的交换耦合常数时,首先分别设置这两个原子的自旋取向,然后再同时设置两个原子的自旋取向,计算出总能即可,而不用选取不同的自旋组态并求解线性方程组.方法特别适合含有数目很大的磁性原子的单分子磁体交换耦合常数的计算.采用新方法计算了Fe7和Fe20配合物分子的交换耦合常数.结果表明,Fe7和Fe20分子中的交换常数都为负,即反铁磁耦合时能量更低,这与类似分子的相关研究相一致. 相似文献