Effect of 3d, 4d, and 5d transition metal doping on damping in permalloy thin films

Rantschler, James; McMichael, Robert D.; Castillo, A.; Shapiro, Alexander J.; Egelhoff, William F.; Maranville, Brian B.; Pulugurtha, D.; Chen, A. P.; Connors, Lawrence Matthew

doi:10.1063/1.2436471

Cited by 113 publications

(85 citation statements)

References 30 publications

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“…2 (top) shows results obtained by substituting Fe and Ni atoms in permalloy by 5d TMs. As found by experiment [16] in all cases nearly linearly with the 5d TM content. The total damping for 10 % 5d TM content shown in the middle panel of Fig.…”

Section: Introductionsupporting

confidence: 70%

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Ab InitioCalculation of the Gilbert Damping Parameter via the Linear Response Formalism

et al. 2011

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A Kubo-Greenwood-like equation for the Gilbert damping parameter α is presented that is based on the linear response formalism. Its implementation using the fully relativistic Korringa-KohnRostoker (KKR) band structure method in combination with Coherent Potential Approximation (CPA) alloy theory allows it to be applied to a wide range of situations. This is demonstrated with results obtained for the bcc alloy system FexCo1−x as well as for a series of alloys of permalloy with 5d transition metals. To account for the thermal displacements of atoms as a scattering mechanism, an alloy-analogy model is introduced. The corresponding calculations for Ni correctly describe the rapid change of α when small amounts of substitutional Cu are introduced.

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Section: Introductionsupporting

confidence: 70%

“…This allows us to study with moderate effort the influence of varying the alloy composition on the damping parameter α. Corresponding work has been done in particular using permalloy as a starting material and adding transition metals (TM) [16] or rare earth metals [17]. Fig.…”

Section: Introductionmentioning

confidence: 99%

Ab InitioCalculation of the Gilbert Damping Parameter via the Linear Response Formalism

et al. 2011

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“…The magnitudes of a and the doping dependence are consistent with Gilbert damping constants in conventional transition metal ferromagnets. In metals, a typically increases with increasing resistivity and is enhanced in alloys with enhanced spin-orbit coupling [42][43][44] . Similarly, in our measurements in (Ga,Mn)As, the increase of a correlates with a sizable increase of the resistivity in the lower Mn-doped samples.…”

Section: Resultsmentioning

confidence: 99%

The essential role of carefully optimized synthesis for elucidating intrinsic material properties of (Ga,Mn)As

et al. 2013

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(Ga,Mn)As is at the forefront of spintronics research exploring the synergy of ferromagnetism with the physics and the technology of semiconductors. However, the electronic structure of this model spintronics material has been debated and the systematic and reproducible control of the basic micromagnetic parameters and semiconducting doping trends has not been established. Here we show that seemingly small departures from the individually optimized synthesis protocols yield non-systematic doping trends, extrinsic charge and moment compensation, and inhomogeneities that conceal intrinsic properties of (Ga,Mn)As. On the other hand, we demonstrate reproducible, well controlled and microscopically understood semiconducting doping trends and micromagnetic parameters in our series of carefully optimized epilayers. Hand-in-hand with the optimization of the material synthesis, we have developed experimental capabilities based on the magneto-optical pumpand-probe method that allowed us to simultaneously determine the magnetic anisotropy, Gilbert damping and spin stiffness constants from one consistent set of measured data.

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“…However, a decrease in α with increasing t e f f can still be seen in both the single-and double-insertion series. One possible reason is the alloying of CoFeB and Ta, as Ta is known to readily intermix with CoFeB [21], and higher damping may be expected from CoFeBTa alloys [28]. The relative percentage of CoFeBTa alloy decreases with increasing CoFeB thickness, coinciding with the α decrease.…”

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Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance

Sabino

Lim

Tran

2014

Appl. Phys. Express

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We show by vector network analyzer ferromagnetic resonance measurements that low Gilbert damping α, down to 0.006, can be achieved in perpendicularly magnetized MgO/CoFeB/MgO thin films with ultrathin insertions of Ta in the CoFeB layer. Although increasing the number of Ta insertions allows thicker CoFeB layers to remain perpendicular, the effective areal magnetic anisotropy does not improve with more insertions, which come with an increase in α.Perpendicular magnetic anisotropy (PMA) is the key to further downscaling of spin transfer torque magnetoresistive random memory devices, as it allows two key requirements to be satisfied: low critical current I c0 and high thermal stability ∆, the latter of which is proportional to the energy barrier E b between the two stable magnetic states. The spin torque switching efficiency, defined as E b /I c0 , is commonly used as a metric to account for both requirements. For a StonerWohlfarth model, it is given by [1] ( /4e) · (η/α), where α is the Gilbert damping parameter, and η is the spin polarization factor, which is related to the tunnel magnetoresistance ratio (TMR) by η = [TMR(TMR + 2)] 1/2 /[2(TMR + 1)]. It thus becomes evident that for high switching efficiency, one has to decrease α while keeping TMR high. Magnetic tunnel junctions (MTJs) based on CoFeB/MgO systems are well known to provide high TMR [2] and have recently been shown to possess PMA, which is attributed to the CoFeB/MgO interface.[3] A Ta layer is usually placed adjacent to the CoFeB to induce the proper crystallization necessary for PMA and high TMR [4]. In Ta/CoFeB/MgO systems, however, spin pumping to the Ta increases α.[5] Moreover, the CoFeB layer also needs to be ultrathin (typically less than 1.5nm) in order to exhibit PMA. [3] To improve the thermal stability as devices are scaled down to smaller diameters, increasing the effective areal anisotropy energy density K e f f t is desired.One approach to address these issues is the use of double-MgO structures, i.e., those in which both the barrier layer and capping layer straddling the free layer are made of MgO. Improved I c0 and/or ∆ have been reported in devices using double MgO free layers. [6,7,8,9] The improvement in thermal stability is attributed to the additional CoFeB/MgO interface, whereas lower I c0 is associated with low α. Indeed, α down to 0.005 has been measured in in-plane MgO/FeB/MgO films,[10] which agrees with device measurements.[11] The stacks investigated in these damping studies, however, did not have the Ta layer used in practical free layers with perpendicular anisotropy. [9,12] In addition, although the interfacial anisotropy in the out-of-plane devices measured by Tsunegi et al.[11] can be as high as 3.3 mJ/m 2 , the effective perpendicular anisotropy was rather low (K e f f t ≈ 0.04mJ/m 2 ) relative to that of a Ta/CoFeB/MgO stack [3]. In this work, we explore the influence of Ta insertions within the CoFeB layer of MgO/CoFeB/MgO films by magnetometry and vector network analyzer ferromagnetic resonance (VNA-...

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Effect of 3d, 4d, and 5d transition metal doping on damping in permalloy thin films

Cited by 113 publications

References 30 publications

Ab InitioCalculation of the Gilbert Damping Parameter via the Linear Response Formalism

Ab InitioCalculation of the Gilbert Damping Parameter via the Linear Response Formalism

The essential role of carefully optimized synthesis for elucidating intrinsic material properties of (Ga,Mn)As

Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance

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