RU2650658C1 - Multilayer magnetoresistive nanowires - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to the field of materials for use in magnetosensor and magnetometric devices, information recording and reading devices. Multilayer magnetoresistive nanowires consist of alternating ferromagnetic and copper layers, nickel-iron layers with thicknesses of 10-30 nm are used as ferromagnetic layers, and the thickness of copper layers is 2-5 nm and the total number of pairs of layers is from 100 to 10 000.

EFFECT: technical result is the production of multilayer magnetoresistive NiFe/Cu nanowires with the GMR coefficients of -18,4…-19,2% and the magnitude of the saturation field of the GMR effect of 0,001-0,0015 T.

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Description

The invention relates to the field of materials for use in magnetosensor and magnetometric devices, devices for recording and reading information.

Metal multilayer low-dimensional structures are currently one of the most interesting objects of study. Due to their unique magnetic and electrical properties, they are widely used in the creation of spintronics devices. A special role is played by the giant magnetoresistive effect (GMR) found in them. The nature of this effect is due to the strong difference in the scattering coefficients of conduction electrons with parallel and antiparallel spin orientations relative to the magnetization vector of the ferromagnetic layers. The practical interest in multilayer structures is due to the possibility of using them as sensors of a magnetic field, sensitive elements of recording and reading heads of magnetic information, solving various types of magnetometry problems - determining the location of an object by the Earth’s magnetic field, measuring the rotation angle and linear displacement in a non-contact way, and recognizing the ferromagnetic image objects.

The practical use of multilayer nanowires is based on two basic principles. The first one is based on the fact that the spatial orientation of the electron spins in the ferromagnetic layers (nanoscale size) of the ferromagnet / diamagnet multilayer nanowires is determined by the magnitudes and directions of the spin-polarized currents flowing through them, the defectiveness of the ferromagnetic layers, the composition and state of the interphase boundaries. This allows using the electric field to control the magnetic structure of ferromagnetic nanolayers. The second principle is due to the fact that the injection of spin-polarized electrons into diamagnetic layers creates a nonequilibrium magnetization in them, which makes it possible to influence the magnitude of the spin current through diamagnetic layers due to a change in their thickness and composition.

Co / Cu multilayer structures are known (D.W. Lee, D.J. Kim, US Patent 6,912,770 B2 (07/05/2005) / Application Number: 10 / 316,783 (12/11/2002)) for use as magnetic field sensors. For coordination with semiconductor devices, a Cu barrier layer (thickness from 10 to 100 nm) is deposited on the Ta, TaN, TiN, or WN substrates by the chemical vapor deposition method (CVD method). Then, a film of a ferromagnet (in particular, Co) is applied by spraying onto a Cu barrier layer, with varying thicknesses (from 10 to 1000 nm). A photosensitive material (photoresist) is applied to the surface of the Co film. Then it is selectively etched with a Co film, forming "trenches". T.O. Co strips are formed on the substrate (width 0.05-1 μm, thickness 0.05-1 μm). After that, in the galvanostatic mode, the “trenches” are filled with a diamagnet (in particular Cu). After this, the multilayer Co / Cu structure is brought to the required thickness and parallelism of the surfaces by the mechanochemical polishing method and then a dielectric layer is applied to the upper surface.

The disadvantage of this material is that the process of forming a multilayer structure is associated with a large number of technological operations, which negatively affects the volume and speed of products. Also, the width of the layers of the diamagnetic metal depends on the parameters of the template (during selective etching), and it is impossible to obtain Cu layers with a width of less than 0.05 μm.

Co / Cu system multilayer nanowires are known (H.-T. Tang, et al, J of Appl. Phys., 2006, V. 99, 033906-1-033906-7). Multilayer nanowires are formed in the pores of alumina by electrodeposition from a combined electrolyte in a potentiostatic mode. The metal layers of Co and Cu are alternately formed. The pore diameter is 300 nm. The maximum GMR effect of 13.5% at room temperature is achieved when the thickness ratio of cobalt and copper layers is 8 nm / 10 nm. In this case, the saturation field of the GMR effect was 0.28–0.38 T.

The disadvantage of this material is the relatively high coercive force of pure cobalt, which leads to high saturation fields (0.28-0.38 T) of the GMR effect in multilayer Co / Cu nanowires.

Closest to the proposed material are multilayer magnetoresistive nanowires, consisting of alternating ferromagnetic layers — CoNi and copper layers — Cu, formed by electrolytic deposition (Patent BY 19142 “Method for producing multilayer nanowires for magnetic field sensors”, Grabchikov SS, Trukhanov A .V., Sharko S.A., dated April 30, 2015). As a prototype, we adopted material based on CoNi / Cu multilayer nanowires formed by electrolytic deposition in a potentiostatic mode from a combined electrolyte into the pores of anodic alumina matrices with a diameter of 100 ± 10 nm. The thickness of each ferromagnetic and copper layer is 25 ± 1 nm and 2 ± 0.3 nm, respectively.

The disadvantage of this material is the relatively low (compared with the proposed material) GMR coefficient (-15.3%) and a significant saturation field of the GMR effect (0.03-0.05 T).

EFFECT: obtaining multilayer magnetoresistive NiFe / Cu nanowires with a GMR coefficient of -18.4 ... -19.2% and a saturation field of the GMR effect of 0.001-0.0015 T.

The technical result is achieved by the fact that NiFe layers with a thickness of 10-30 nm are used as ferromagnetic layers, and the thickness of copper layers is 2-5 nm and the total number of layer pairs is from 100 to 10,000.

The invention consists in the following. Multilayer nanowires of the NiFe / Cu system are deposited into the pores of the matrix of anodic alumina (pore diameter 100 ± 10 nm) by electrodeposition in a potentiostatic mode. Electrodeposition is carried out using a hardware-software complex based on the PI-50-1.1 potentiostat (GOST 22261-82) with an electrochemical cell and the PR-8 programmer (GOST 25272-14), designed to set the signal. A silver-silver reference electrode EVL-1M 3.1 (TU25-05 (1E2.840.217) -78), having a potential of 201 ± 3 mV relative to a normal hydrogen electrode, is designed to set and maintain the deposition potential when operating in the potentiostatic mode. The current strength in the electric circuit is controlled by an ammeter M325-1.5 (GOST 871 1-93), which has an accuracy class of 0.2. To obtain multilayer nanowires, the pulsed electrodeposition method is used (A V Trukhanov, SS Grabchikov, SA Sharko, SV Trukhanov, K L Trukhanova, O S Volkova, and A Shakin, Magnetotransport properties and calculation of the stability of GMR coefficients in CoNi / Cu multilayer quasi -one-dimension structures, Materials research express Vol. 3, No. 6, (2016)) from a combined electrolyte. The principle of this method is based on the fact that ferromagnetic metals of the iron group (Fe, Co. Ni, as well as their alloys) and noble metals (Cu, Ag, Au, Pt) can be used respectively as ferromagnetic and diamagnetic layers. The preparation of multilayer nanowires by electrolytic deposition from the same electrolyte is based on the fact that the equilibrium reduction potential of ferromagnetic and noble metal ions differs by more than 400 mV. Therefore, at low deposition potentials, only metals such as Cu, Ag, etc. will be reduced. At more negative potentials, both Cu and ferromagnetic metals or their alloys are deposited. But if you set the concentration of Cu ions in the electrolyte is much lower than the concentration of ferromagnetic ions (about 1% of the concentration of magnetic metal ions), then due to diffusion difficulties in the transfer of Cu ions to the cathode, the deposition rate of Cu layers will be limited, regardless of the magnitude of the applied potential.

The deposition of multilayer NiFe / Cu nanowires into the pores of the alumina matrices is made from a combined electrolyte of the following composition (g / l): NiSO ₄ ⋅ 7H ₂ O - 210 g / l; MgSO ₄ - 60 g / l; FeSO ₄ ⋅ 7H ₂ O - 15 g / l; NiCl ₂ - 20 g / l; H ₃ BO ₃ - 30 g / l; saccharin - 1; CuSO ₄ ⋅ 5H ₂ O - 35 g / l; KNaC ₄ H ₄ O ₆ 4H ₂ O - 25 g / l; pH = 2.4-2.6, T = 50-60 ° C (nickel is used as an anode).

The ratio between the concentrations of salts of NiSO ₄ ⋅ 7H ₂ O and FeSO ₄ ⋅ 7H ₂ O (210/15 g / l) in the electrolyte was due to the fact that at this concentration alloy compositions (Ni ₈₀ Fe ₂₀ ) are formed with a minimum coercive force and maximum magnetic permeability values.

The deposition modes of multilayer nanowires were as follows: ϕNiFe = -1.8 ... -2.3 V; ϕCu = -0.2-0.4 V. Under these conditions, the average deposition rate of individual layers is V _NiFe = ~ 8-10 nm / s; v _Cu = ~ 0.1-0.5 nm / s. The thickness of the ferromagnetic layer is 10-30 nm, the thickness of the Cu layer is 2-5 nm. The thickness of the matrix of aluminum oxide is ~ 2-120 microns. The pore diameter in the matrices is ~ 100 ± 10 nm.

The GMR coefficient of multilayer nanowires was calculated on the basis of the measurement data of the electrical resistance by the two-contact method for fixed values of magnetic fields in the range up to 0.13 T at room temperature according to the following formula:

where R (B) is the electrical resistance of multilayer NiFe / Cu nanowires in an external magnetic field B, R ₀ is the electrical resistance of multilayer NiFe / Cu nanowires without a magnetic field.

Example 1

Multilayer magnetoresistive nanowires NiFe / Cu with layer thicknesses: ferromagnetic layer NiFe 20 nm; diamagnetic Cu layer - 2 nm; the total number of pairs of NiFe / Cu layers is 1000; the total thickness of the matrix of anodic alumina is 20-25 microns. Multilayer nanowires of the NiFe / Cu system are deposited into the pores of the matrix of anodic alumina (pore diameter 100 ± 10 nm) by electrodeposition in a potentiostatic mode. The deposition of multilayer NiFe / Cu nanowires into the pores of the alumina matrices is made from a combined electrolyte of the following composition (g / l): NiSO ₄ ⋅ 7H ₂ O - 210 g / l; MgSO ₄ - 60 g / l; FeSO ₄ ⋅ 7H ₂ O - 15 g / l; NiCl ₂ - 20 g / l; H ₃ BO ₃ - 30 g / l; saccharin - 1; CuSO ₄ ⋅ 5H ₂ O - 35 g / l; KNaC ₄ H ₄ O ₆ 4H ₂ O - 25 g / l; pH = 2.4-2.6, T = 50-60 ° C (nickel is used as an anode). The deposition modes of multilayer nanowires: ϕNiFe = -1.8 ... -2.3V; ϕCu = -0.2-0.4V. Under these conditions, the average deposition rate of individual layers is v _NiFe = ~ 8-10 nm / s; v _Cu = ~ 0.1-0.2 nm / s. The deposition time of one partial ferromagnetic layer of NiFe is 1.6-2 s. The deposition time of one partial diamagnetic Cu layer is 4-8 s. The GMR coefficient is -18.7%. The value of the saturation field of the GMR effect is 0.0013 T (Fig. 1)

Example 2

Multilayer magnetoresistive nanowires NiFe / Cu with layer thicknesses: ferromagnetic layer NiFe 30 nm; diamagnetic Cu layer - 5 nm; the total number of pairs of NiFe / Cu layers is 1000; the total thickness of the matrix of anodic alumina is 35-38 microns. Multilayer nanowires of the NiFe / Cu system are deposited into the pores of the matrix of anodic alumina (pore diameter 100 ± 10 nm) by electrodeposition in a potentiostatic mode. The deposition of multilayer NiFe / Cu nanowires into the pores of the alumina matrices is made from a combined electrolyte of the following composition (g / l): NiSO ₄ ⋅ 7H ₂ O - 210 g / l; MgSO ₄ - 60 g / l; FeSO ₄ ⋅ 7H ₂ O - 15 g / l; NiCl ₂ - 20 g / l; H ₃ BO ₃ - 30 g / l; saccharin - 1; CuSO ₄ ⋅ 5H ₂ O - 35 g / l; KNaC ₄ H ₄ O ₆ 4H ₂ O - 25 g / l; pH = 2.4-2.6, T = 50-60 ° C (nickel is used as an anode). The deposition modes of multilayer nanowires: ϕNiFe = -1.8 ... -2.3V; ϕCu = -0.2-0.4V. Under these conditions, the average deposition rate of individual layers is v _NiFe = ~ 8-10 nm / s; v _Cu = ~ 0.1-0.2 nm / s. The deposition time of one partial ferromagnetic layer of NiFe is 3-3.75 s. The deposition time of one partial diamagnetic Cu layer is 12.5-25 s. The GMR coefficient is -18.4%. The value of the saturation field of the GMR effect is 0.0015 T (Fig. 2)

Example 3

Multilayer magnetoresistive nanowires NiFe / Cu with layer thicknesses: ferromagnetic layer NiFe 30 nm; diamagnetic Cu layer - 2 nm; the total number of pairs of NiFe / Cu layers is 1000; the total thickness of the matrix of anodic alumina is 30-35 microns. Multilayer nanowires of the NiFe / Cu system are deposited into the pores of the matrix of anodic alumina (pore diameter 100 ± 10 nm) by electrodeposition in a potentiostatic mode. The deposition of multilayer NiFe / Cu nanowires into the pores of the alumina matrices is made from a combined electrolyte of the following composition (g / l): NiSO ₄ ⋅ 7H ₂ O - 210 g / l; MgSO ₄ - 60 g / l; FeSO ₄ ⋅ 7H ₂ O - 15 g / l; NiCl ₂ - 20 g / l; H ₃ BO ₃ - 30 g / l; saccharin - 1; CuSO ₄ ⋅ 5H ₂ O - 35 g / l; KNaC ₄ H ₄ O ₆ 4H ₂ O - 25 g / l; pH = 2.4-2.6, T = 50-60 ° C (nickel is used as an anode). The deposition modes of multilayer nanowires: ϕNiFe = -1.8 ... -2.3V; ϕCu = -0.2-0.4V. Under these conditions, the average deposition rate of individual layers is v _NiFe = ~ 8-10 nm / s; v _Cu = ~ 0.1-0.2 nm / s. The deposition time of one partial ferromagnetic layer of NiFe is 3-3.75 s. The deposition time of one partial diamagnetic Cu layer is 5-10 s. The GMR coefficient is - 19.2%. The value of the saturation field of the GMR effect is 0.0013 T (Fig. 3)

Claims (1)

Multilayer magnetoresistive nanowires, consisting of alternating ferromagnetic and copper layers, characterized in that the ferromagnetic layers are made in the form of NiFe layers with a thickness of 10-30 nm, and copper layers with a thickness of 2-5 nm, with a total number of pairs of layers ranging from 100 up to 10,000.

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