Perpendicular exchange bias effect in sputter-deposited CoFe/IrMn bilayers

Chen, Junyang; Thiyagarajah, Naganivetha; Xu, Hao; Coey, J. M. D.

doi:10.1063/1.4871711

Cited by 30 publications

(31 citation statements)

References 27 publications

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“…As summarized in Fig. 1(c), finite exchange bias only becomes evident for NiFe/Cu/IrMn/CoFe samples with t IrMn ≥ 3 nm, consistent with previous reports [36,37]. With field applied orthogonal to the exchange bias direction, while NiFe is essentially saturated at < ∼ 1 mT, CoFe does not saturate up to > ∼ 100 mT ( Fig.…”

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confidence: 90%

Spin decoherence independent of antiferromagnetic order in IrMn

et al. 2019

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We investigate the impact of pinned antiferromagnetic order on the decoherence of spin current in polycrystalline IrMn. In NiFe/Cu/IrMn/CoFe multilayers, we coherently pump an electronic spin current from NiFe into IrMn, whose antiferromagnetic order is globally pinned by static exchangebias coupling with CoFe. We observe no anisotropic spin decoherence with respect to the orientation of the pinned antiferromagnetic order. We also observe no difference in spin decoherence for samples with and without pinned antiferromagnetic order. Moreover, although there is a pronounced resonance linewidth increase in NiFe that coincides with the switching of IrMn/CoFe, we show that this is not indicative of anisotropic spin decoherence in IrMn. Our results demonstrate that the decoherence of electron-mediated spin current is remarkably insensitive to the magnetization state of the antiferromagnetic IrMn spin sink.A spin current is said to be coherent when the spin polarization of its carriers, e.g., electrons, is locked in a uniform precessional phase. How a spin current loses its coherence, particularly as it interacts with magnetic order, is a crucial fundamental question in spintronics [1]. In a ferromagnetic metal (FM), an electronic spin current polarized transverse to the magnetization dephases quickly in the uniform ferromagnetic exchange field [2,3]. Experiments of ferromagnetic resonance (FMR) spin pumping [4][5][6], where a coherently excited spin current propagates from a FM spin source to a FM spin sink [7], show the transverse spin coherence length in FMs to be as short as ≈1 nm [8]. The dephasing of transverse spin polarization s also gives rise to a spin-transfer torque, ∝ m × s × m, acting on the magnetization m of the FM spin sink [2,3,9,10].For antiferromagnetic metals (AFMs) with staggered exchange fields, a fundamental understanding of spin transport has yet to be developed by experiment. Although the transverse spin coherence length can in principle be 1 nm [11][12][13], an electronic spin current polarized transverse to the antiferromagnetic order parameter (Néel vector l) is expected to dephase in the diffusive limit of transport [12,14]. Such spin dephasing in AFMs generates a spin-transfer torque, ∝ l × s × l [13-15], which may be crucial for emerging antiferromagnetic spintronic technologies [16][17][18][19][20].Furthermore, spin dephasing in an AFM with a uniform Néel vector may yield anisotropic decoherence, where spin absorption by the AFM is enhanced when l ⊥ s [21].By contrast, polycrystalline thin films of AFMs by themselves do not exhibit anisotropic spin decoherence on a macroscopic scale, since the grains contain a distribution of Néel vector orientations that averages out the anisotropy [22]. While polycrystalline AFMs have found commercial applications (i.e., pinning ferromagnetic layers in spin valves) [23] and been used as spin sinks [8,22,[24][25][26][27][28], their nonuniform, unpinned antiferromagnetic order poses a challenge for gaining fundamental insight into spin decoherence.To ali...

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confidence: 90%

Spin decoherence independent of antiferromagnetic order in IrMn

et al. 2019

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“…Basic magnetic properties of the new multiferroic EB system were shown in Figure . The magnetic hysteresis loops can be regulated by the thickness of IrMn layer (Figure a); the intensity of EB increases with the IrMn thickness until reaches the saturation point, in which the AFM grain volume is large enough to pin all the FM spins at the interface . The results shown in Figure b demonstrate that the decrease in Pt thickness is acceptable since the variation trend of IrMn thickness is consistent with Figure a.…”

Section: Resultssupporting

confidence: 54%

Voltage Control of Perpendicular Exchange Bias in Multiferroic Heterostructures

Zhang

et al. 2019

Adv Elect Materials

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is one of the most decisive factors in the excellent performance of spintronic devices. [1,2] Researches have intensely studied EB properties due to the importance applications in magnetic random access memories and magnetoresistive read heads based on spin valves or tunnel junctions. [3] If EB is combined with the perpendicular magnetic anisotropy (PMA), [1] it is promising to develop magnetic devices with ultrahigh density. [4] One existing challenge for AFM spintronics is the effective regulation of magnetization. [5] Although the AFM materials are essentially magnetic, they do not have macroscopic magnetization due to the alternatively antiparallel magnetic spins. [6] Therefore, AFM materials are very insensitive to the magnetic perturbation. [7] As an alternative, voltage control of magnetism provides a promising way in realizing next generation of fast, compact, and energy-efficient magnetic memories and sensors. [8][9][10] There are some studies related to the piezoelectric strain-controlled EB with in-plane anisotropy, [9,11,12] demonstrating the feasibility of using electric field (E-field) to manipulate AFM moments and domains. E-field induced interfacial strain mediation can also regulate the spin structure of AFM materials [13] with an excellent fatigue durability, [14] which is promising in anti-ferromagnetic piezospintronics. Nevertheless, because the alternative spins of AFM materials are strongly pinned, [15] the existing E-field controls of EB and AFM spins are usually confined at a low temperature [1,16] or require a large H-field assistance. [13] Although the magnetoelectric (ME) switching of perpendicular EB has been studied by changing the interfacial exchange and magnetization at low temperature, [1] the control of perpendicular EB by strain-mediated ME coupling has not been demonstrated yet. Therefore, we considered perpendicular EB on ferroelectric Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT) [17] substrate to realize the electrical modulation of anti-ferromagnetism.In this work, we utilized vibrating sample measurements (VSM) and ferromagnetic resonance (FMR) to study the strainmediated voltage control effect. Both the film fabrication and characterization were carried at room temperature, which has overcome the requirement of a high-temperature magnetic annealing during the EB formation [18] as well as the difficulty of Perpendicular exchange bias (EB), which combines perpendicular magnetic anisotropy and ferromagnetic (FM)-anti-ferromagnetic (AFM) exchange coupling, is extremely important in high-density AFM spintronics. However, the effective modulation of EB remains challenging, since the alternant spins at the AFM/ FM interface are strongly pinned by the AFM layer. Voltage tuning of EB through magnetoelectric coupling provides a potential way to achieve rapid magnetization switching in an energy-efficient manner. Nevertheless, the interfacial strain mediation of perpendicular EB induced by E-field remains unexplored. In this work, perpendicular EB nanostructure by room-temperature fabri...

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“…From the slope of this figure and the saturation magnetization determined earlier, one can determine the interface energy per unit area [7,36,37], also called interfacial exchange coupling, ∆ · · , which enables a comparison with other exchange bias systems. For the interfacial exchange coupling we obtain a value of ∆ 0.53 0.02 / , which exceeds the values for all metallic antiferromagnets listed in Table 3 of reference [7] and is almost five times as big as the value reported in reference [38] for perpendicular CoFe/IrMn bilayers, which confirms the strong interfacial exchange coupling in our film series.…”

Section: B2 Quasistatic Magnetometrysupporting

confidence: 63%

Broadband ferromagnetic resonance characterization of anisotropies and relaxation in exchange-biased IrMn/CoFe bilayers

et al. 2017

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The magnetization dynamics of exchange biased IrMn/CoFe bilayers have been investigated using broadband and in-plane angle dependent ferromagnetic resonance spectroscopy. The interface energy of the exchange bias effect in these bilayers exceeds values previously reported for metallic antiferromagnets. A strong perpendicular magnetic anisotropy and a small in-plane uniaxial anisotropy are also observed in these films. The magnetization relaxation of the bilayers has a strong unidirectional contribution, which is in part caused by two-magnon scattering. However, a detailed analysis of in-plane angle and thickness dependent linewidth data strongly suggests the presence of a previously undescribed unidirectional relaxation mechanism.2

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Perpendicular exchange bias effect in sputter-deposited CoFe/IrMn bilayers

Cited by 30 publications

References 27 publications

Spin decoherence independent of antiferromagnetic order in IrMn

Spin decoherence independent of antiferromagnetic order in IrMn

Voltage Control of Perpendicular Exchange Bias in Multiferroic Heterostructures

Broadband ferromagnetic resonance characterization of anisotropies and relaxation in exchange-biased IrMn/CoFe bilayers

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