Negative anisotropic magnetoresistance in 3d metals and alloys containing iridium

We present the Co-Gd composition dependence of the spin-Hall magnetoresistance (SMR) and anisotropic magnetoresistance (AMR) for ferrimagnetic Co 100-x Gd x / Pt bilayers. With Gd concentration x, its magnetic moment increasingly competes with the Co moment in the net magnetization. We find a nearly compensated ferrimagnetic state at x = 24. The AMR changes sign from positive to negative with increasing x, vanishing near the magnetization compensation. On the other hand, the SMR does not vary significantly even where the AMR vanishes. These experimental results indicate that very different scattering mechanisms are responsible for AMR and SMR. We discuss a possible origin for the alloy composition dependence.Page 5 the anisotropic magnetoresistance (AMR) that occur simultaneously in all-metal magnetic bilayers, which should help to establish microscopic models for both effects.We report the different composition dependences of SMR and AMR for the Co-Gd / Pt bilayers with in-plane magnetization. The sign of the AMR monotonically changes from positive to negative by increasing the Gd concentration and vanishes near the magnetization compensation composition. On the other hand, the SMR remains finite even when the AMR vanishes, which is a direct proof for different physics. We interpret the composition dependence of the SMR in terms of a spin mixing conductance that, in contrast to the conventional wisdom, depends on the magnet. Experimental ProcedureThin films were deposited on a thermally oxidized Si substrate using an ultrahigh vacuum compatible magnetron sputtering system with the base pressure below 2 × 10 -7 Pa. First, a 4 nm-thick Cr buffer was deposited on the Si-O substrate. Then Co and Gd were co-deposited to form the Co 100-x Gd x layers with a thickness of 30 nm. Finally, a 4 nm-thick Pt layer was deposited. All the layers were deposited at room temperature. By tuning the sputtering powers of Co and Gd targets, the Gd concentration x (at. %) was widely varied from x = 0 to x = 45. Except for x = 0, i.e. pure cobalt, the Co-Gd layers were amorphous alloys, as confirmed by reflection high energy electron diffraction (RHEED) in Fig. 1(c). In contrast to the amorphous

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“…6(b)). Pure Co shows a positive AMR [29] while a negative AMR has been reported for a Gd single crystal [30].…”

Section: Pagementioning

confidence: 75%

Spin-Hall and anisotropic magnetoresistance in ferrimagnetic Co-Gd/Pt layers

Zhou

Seki

Kubota

et al. 2018

Phys. Rev. Materials

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“…[6] and reproduced in column 4 together with their grain sizes in column 6. We have also listed relevant literature data for Ni thin films [26][27][28][29] which are presumably also nanocrystalline.…”

Section: Nanocrystalline Nimentioning

confidence: 99%

Room-temperature magnetoresistance of nanocrystalline Ni metal with various grain sizes

et al. 2020

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The room-temperature magnetoresistance (MR) characteristics of nanocrystalline (nc) Ni metal with various grain sizes (between 30 and 100 nm) are investigated in this work for the first time. The nc-Ni foils were produced by electrodeposition and the results are compared with data measured on coarse-grained (bulk) pure Ni metal samples prepared by cold-rolling and annealing. The MR(H) curves measured in magnetic fields up to H 9 kOe are analyzed in detail to determine the anisotropic magnetoresistance (AMR) ratio. The magnitude of the AMR ratio was found to be around 2.5% for bulk Ni and in the range from about 2 to 2.5% for the nc-Ni samples, the latter data not exhibiting a systematic dependence on the grain size. On the other hand, the field-induced resistivity anisotropy splitting ρ AMR in the magnetically saturated state of the nc-Ni series was found to be proportional to the zero-field resistivity of the same samples with different grain sizes. The slope of this proportionality relation provided an AMR ratio of 2.4% for all nc-Ni samples, matching well the value for the bulk Ni samples. Thus, the AMR ratio for polycrystalline Ni metal seems to be fairly independent of the microstructural features. This also means that the AMR ratio is an inherent characteristic of the Ni metal matrix and it remains the same even if the matrix resistivity changes (e.g., by introducing grain boundaries) without noticeably modifying the electronic density of states at least in the vicinity of the Fermi level.

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“…Weak ferromagnet 21) bcc Fe 0.0030 at 300 K (ref. 8 the conduction states of the σ spin, while sσ → dς was the scattering process from the conduction state of the σ spin to the σ spin state in the localized d states of the ς spin. On the other hand, Malozemoff 9,10) extended the CFJ model to a more general model which was applicable to the weak ferromagnet as well as the strong ferromagnet.…”

Section: Categorymentioning

confidence: 99%

Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe₄N, and Half-Metallic Ferromagnet: A Systematic Analysis

et al. 2012

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We theoretically analyze the anisotropic magnetoresistance (AMR) effects of bcc Fe (þ), fcc Co (þ), fcc Ni (þ), Fe 4 N (À), and a half-metallic ferromagnet (À). The sign in each parenthesis represents the sign of the AMR ratio observed experimentally. We here use the two-current model for a system consisting of a spin-polarized conduction state and localized d states with spin-orbit interaction. From the model, we first derive a general expression of the AMR ratio. The expression consists of a resistivity of the conduction state of the spin ( ¼ " or #), s , and resistivities due to s-d scattering processes from the conduction state to the localized d states. On the basis of this expression, we next find a relation between the sign of the AMR ratio and the s-d scattering process. In addition, we obtain expressions of the AMR ratios appropriate to the respective materials. Using the expressions, we evaluate their AMR ratios, where the expressions take into account the values of s# = s" of the respective materials. The evaluated AMR ratios correspond well to the experimental results.

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Negative anisotropic magnetoresistance in 3d metals and alloys containing iridium

Cited by 40 publications

References 10 publications

Spin-Hall and anisotropic magnetoresistance in ferrimagnetic Co-Gd/Pt layers

Spin-Hall and anisotropic magnetoresistance in ferrimagnetic Co-Gd/Pt layers

Room-temperature magnetoresistance of nanocrystalline Ni metal with various grain sizes

Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe₄N, and Half-Metallic Ferromagnet: A Systematic Analysis

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Negative anisotropic magnetoresistance in 3d metals and alloys containing iridium

Cited by 40 publications

References 10 publications

Spin-Hall and anisotropic magnetoresistance in ferrimagnetic Co-Gd/Pt layers

Spin-Hall and anisotropic magnetoresistance in ferrimagnetic Co-Gd/Pt layers

Room-temperature magnetoresistance of nanocrystalline Ni metal with various grain sizes

Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe4N, and Half-Metallic Ferromagnet: A Systematic Analysis

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Product

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Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe₄N, and Half-Metallic Ferromagnet: A Systematic Analysis