JP2018181975A - Method of increasing spin-orbit interaction and spin device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spin device which can be put into practical use at a lower cost. SOLUTION: Nitrogen is added to a metal material layer made of Cu to increase the spin-orbit interaction of the metal material layer. Cu is a material having a weak spin-orbit interaction and cannot be applied to a spin device. On the other hand, by adding nitrogen as an impurity to the copper thin film (metal material layer), the spin-orbit interaction is increased, and the spin device can be applied. With inexpensive materials Cu and nitrogen, the strength of spin-orbit interaction can be made comparable to that of rare metals such as platinum, and these expensive material systems can be replaced with inexpensive materials, and spin can be achieved. This leads to device cost reduction. The spin injection magnetic memory includes a spin injection layer (metal material layer to which nitrogen is added) 101 and a free layer 102 made of a ferromagnet formed on the spin injection layer 101. [Selection diagram] Fig. 5

Description

  The present invention relates to a method of increasing spin-orbit interaction which increases spin-orbit interaction of a metal material, and a spin device using the metal material which has increased spin-orbit interaction.

  Materials with strong spin-orbit interaction are important for spin current generation through the spin Hall effect and magnetization reversal by spin orbit torque, and a search for materials capable of highly efficient spin current generation is actively conducted.

Y. Niimi et al., "Giant Spin Hall Effect Induced by Skew Scattering from Bismuth Impurities inside Thin Film CuBi Alloys", Physical Review Letters, PRL 109, 156602, 2012. C. Navio et al., "Intrinsic surface band bending in Cu3N (100) ultrathin films", Physical Review B, vol. 76, no. 8, 085105, 2007. S. Hikami, et al., "Spin-Orbit Interaction and Magnetoresistance in the Two-Dimensional Random System", Prog. Theor. Phys. Vol. 63, no. 2, pp. 707-710, 1980, Progress Letters.

  However, many of the material systems with strong spin-orbit interaction are rare metals such as platinum, tantalum and tungsten, and these material systems become expensive in consideration of practical use of spin devices, and their element strategies From the point of view of

  The present invention has been made to solve the above problems, and it is an object of the present invention to enable spin devices to be put to practical use at lower cost.

  The method of increasing the spin-orbit interaction according to the present invention is to add nitrogen to the metal material layer made of metal to increase the spin-orbit interaction of the metal material layer. The metal is Cu.

  The spin device according to the present invention is composed of a metal material layer made of a metal to which nitrogen is added.

  In the spin device, the spin device is a spin injection magnetic memory, and is formed on a spin injection layer made of a metal material layer, a free layer made of a ferromagnetic material formed on the spin injection layer, and a free layer A tunnel barrier layer, a fixed layer of ferromagnetic material formed on the tunnel barrier layer, and an upper electrode formed on the fixed layer. The metal is Cu.

  As described above, according to the present invention, since the metal material layer made of Cu to which nitrogen is added is used, the excellent effect that the spin device can be put to practical use at lower cost can be obtained.

FIG. 1 is a plan view showing the configuration of a hole bar element manufactured to measure the characteristics of copper nitride in the embodiment. FIG. 2 is a characteristic diagram showing the change in the specific resistance at a temperature of 2 K of the copper nitride thin film produced by reactive sputtering in the embodiment with respect to the nitrogen partial pressure. FIG. 3 is a characteristic diagram showing the observation results of the localized phenomenon of the copper nitride thin film produced by reactive sputtering in the embodiment. FIG. 4 is a characteristic diagram showing a change in spin relaxation length of a copper nitride thin film produced by reactive sputtering in the embodiment with respect to a nitrogen partial pressure. FIG. 5 is a configuration diagram showing a configuration of a spin injection magnetic memory which is a spin device in the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described.

  The method of increasing the spin-orbit interaction in the embodiment of the present invention is to add nitrogen to the metal material layer made of metal to increase the spin-orbit interaction of the metal material layer. The metal is a nonmagnetic metal, for example, copper (Cu).

  As well known, Cu is a material having weak spin-orbit interaction and can not be applied to spin devices. On the other hand, as a result of intensive studies and studies by the inventors, by adding nitrogen as an impurity to a copper thin film (metal material layer), the spin-orbit interaction is increased, which is applicable to spin devices. I found something. The inexpensive materials Cu and nitrogen make it possible to make the strength of spin-orbit interaction comparable to that of rare metals such as platinum, make it possible to replace these expensive material systems with inexpensive materials, and It leads to the cost reduction of the device.

  Until now, the technology which produces large spin orbital interaction is proposed by making a small amount of rare metal elements, such as Bi, mix in thin films, such as Cu with small spin orbital interaction, (nonpatent literature 1). However, in this technology, since rare metals are used, it is not easy to reduce the cost.

  Recently, a technique has also been proposed which increases the strength of spin-orbit interaction in metals by adding oxygen as an impurity. However, when oxygen is introduced as an impurity into the metal thin film, the electronic structure becomes insulator, which makes it difficult to take ohmic contact, and in industrial application, it is not easy to apply to a spin device. On the other hand, in the metal added with nitrogen, the electronic structure becomes semiconductive (see Non-Patent Document 2), it is relatively easy to take ohmic contact, and application to a spin device is easy.

Next, results of actually producing Cu to which nitrogen is added will be described. Reactive sputtering is performed using a well-known reactive RF magnetron sputtering apparatus, targeting Cu, nitrogen and argon at a pressure of 0.5 Pa, changing the partial pressure ratio, and adding nitrogen-added Cu (copper nitride) A thin film was prepared. The conditions for forming the copper nitride thin film are shown in Table 1 below. In the table, “sccm” is a unit of flow rate, and indicates that a fluid of 0 ° C. · 1013 hPa flows 1 cm ³ per minute. Further, more detailed conditions in which the nitrogen flow rate is 0.7 to 3 sccm are nitrogen partial pressures of 0.032 Pa, 0.045 Pa, 0.065 Pa, 0.083 Pa, and 0.1 Pa.

  Next, the manufactured copper nitride thin film was patterned by argon ion milling using a mask pattern formed by a known photolithography technique to manufacture a Hall bar element 300 μm in length and 10 μm in thickness (see FIG. 1). ). Samples of five types of Hall bar elements were manufactured for each of the nitrogen partial pressures described above.

The strength of the spin-orbit interaction was evaluated from the magnetotransport properties using the produced Hall bar element. The magnetic conductivity measurement and the hole measurement were performed in a state where the temperature of the above-mentioned Hall bar element was 2 K in a ⁴ He cryostat. The resistivity at 2 K exhibits a behavior which exponentially increases with the nitrogen partial pressure at the time of film formation, as shown in FIG.

  In the evaluation of the strength of spin-orbit interaction, we focused on weakly localized and weakly delocalized phenomena of copper thin film and copper nitride thin film. The weak localization phenomenon refers to the case where a positive magnetic conductivity is exhibited when a plane direct magnetic field is applied to the magnetic conductivity of the zero magnetic field, and is observed when the spin-orbit interaction is weak. On the other hand, the weak delocalization phenomenon refers to a case where a negative magnetic conductivity is exhibited when a plane direct magnetic field is applied to the magnetic conductivity of the zero magnetic field. In the weak delocalization phenomenon, the value of the magnetic field where the magnetic conductivity takes an extreme value is proportional to the strength of the spin-orbit interaction. It is possible to know the change in the strength of spin-orbit interaction.

  The spin relaxation length can be obtained as a fitting parameter by fitting the theoretical formula (see Non-Patent Document 3) to the change in magnetic conductivity with respect to the in-plane magnetic field. The spin relaxation length is the propagation distance until the direction of a large number of electron spins aligned at the beginning becomes apart, and is inversely proportional to the strength of the spin-orbit interaction. Therefore, it is possible to quantitatively discuss the strength of the spin-orbit interaction using the spin relaxation length.

  As shown in FIG. 3, from the dependence of the magnetic conductivity on the in-plane magnetic field, a weak localization phenomenon was observed in the copper thin film, whereas a weak delocalization phenomenon was observed in the copper nitride thin film. Also, the value of the magnetic field at which the magnetic conductivity takes an extreme value systematically increased with respect to the nitrogen partial pressure. From this, it is qualitatively clarified that the addition of nitrogen to the copper thin film increases the strength of the spin-orbit interaction.

  In addition, it can be seen that the strength of the spin-orbit interaction can be controlled by the nitrogen partial pressure at the time of film formation described above. As shown in FIG. 4, the spin relaxation length of the copper nitride thin film obtained by the theoretical equation fitting decreases linearly with the nitrogen partial pressure, and the value of the spin relaxation length is smaller than that of the copper thin film. It became clear that it became 1/10 or less. This value is comparable to that of platinum and bismuth having strong spin-orbit interaction, and copper nitride is considered to be a substitute for these material systems.

  Next, the spin device in the embodiment of the present invention will be described. The spin device in the present invention is characterized by being composed of a metal material layer made of a metal to which nitrogen is added as described above.

  For example, the spin device is a spin injection magnetic memory shown in FIG. The spin injection magnetic memory includes a spin injection layer (a metal material layer to which nitrogen is added) 101 and a free layer 102 made of a ferromagnetic material formed on the spin injection layer 101. The spin injection magnetic memory further includes a tunnel barrier layer 103 formed on the free layer 102 and a fixed layer 104 formed of a ferromagnetic material formed on the tunnel barrier layer 103. An upper electrode 105 is formed on the fixed layer 104. In the embodiment, the spin injection layer 101 is formed of a metal material layer made of a metal to which nitrogen is added. The metal is copper.

  The spin injection magnetic memory generates a spin current above the spin injection layer 101 by generating a difference between the flow of electrons 111 in the upward spin and electrons 112 in the downward spin by flowing a current through the spin injection layer 101. Rewriting is performed by reversing the magnetization direction in the free layer 102. The magnetization direction of the fixed layer 104 is fixed. When the direction of magnetization is the same between the free layer 102 and the fixed layer 104, the value of the electrical resistance in the stacking direction is low, and when the directions of magnetization are opposite, the electrical resistance is high. The difference in resistance value is the difference in stored data. Data can be read as the difference in resistance value between the spin injection layer 101 and the upper electrode 105 as the lower electrode.

  It is important that the spin injection layer is made of a material having strong spin-orbit interaction, and generally, heavy elements such as platinum and tantalum are used. On the other hand, in the embodiment, since the spin injection layer 101 is formed of copper nitride, the spin injection magnetic memory can be manufactured more inexpensively.

  As described above, according to the present invention, since nitrogen is added to a nonmagnetic metal such as copper and used, a spin device can be put to practical use at lower cost. For example, the cost can be suppressed to 1/10 to 1/100 in the case where a platinum thin film is used for the same purpose and in the case where a nitrogen-added copper thin film is used. As a result, it is possible to make practicalization and mass production of spin devices more realistic.

  The present invention is not limited to the embodiments described above, and many modifications and combinations can be made by those skilled in the art within the technical concept of the present invention. It is clear. For example, although the case where the layer of Cu to which nitrogen is added is formed by the reactive sputtering method has been described above as an example, the present invention is not limited thereto, and Cu formed by the plating method or sputtering method is Nitrogen may be added by disposing the

  101 ... spin injection layer, 102 ... free layer, 103 ... tunnel barrier layer, 104 ... fixed layer, 105 ... top electrode, 111 ... electron of upward spin, 112 ... electron of downward spin.

Claims (5)

  A method of enhancing spin-orbit interaction, comprising adding nitrogen to a metal-material layer made of metal to increase spin-orbit interaction of the metal-material layer. In the method of increasing spin-orbit interaction according to claim 1,
The method for increasing spin-orbit interaction, wherein the metal is Cu.   A spin device comprising a metal material layer made of a metal to which nitrogen is added. In the spin device according to claim 3,
The spin device is a spin injection magnetic memory,
A spin injection layer comprising the metal material layer;
A free layer of ferromagnetic material formed on the spin injection layer;
A tunnel barrier layer formed on the free layer;
A fixed layer of ferromagnetic material formed on the tunnel barrier layer;
An upper electrode formed on the fixed layer. The spin device according to claim 3 or 4
The spin device characterized in that the metal is Cu.