Experimental Report

実験報告書様式（プロジェクト利用）
承認日 Date of Approval 2013/05/27
承認者 Approver TAKEDA Masayasu
提出日 Date of Report 2013/05/27

実験課題番号 Project No.

装置責任者 Name of Instrument scientist

2013P0302

武田全康

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Research on Correlation between Magnetic Structure and Function inSHARAKU/BL17

Magnetic Multilayers Relating to Spintronics

利用期間 Dates of experiments

実験責任者名 Name of principal investigator2012/06/07 日 09:00 〜 15 日 09:00

TAKEDA Masayasu

2013/01/15 日 09:00 〜 17 日 09:00

所属 Affiliation

2013/01/17 日 21:00 〜 18 日 21:00

Japan Atomic Energy Agency

2013/01/29 日 09:00 〜 30 日 09:00
2013/01/30 日 21:00 〜 05 日 09:00

１．研究成果概要（試料の名称、組成、物理的・化学的性状を明記するとともに、実験方法、利用の結果得られた主なデータ、考察、結論、図表等を記述してください。
Outline of experimental results (experimental method and results should be reported including sample
information such as composition, physical and/or chemical characteristics.)
The aim of this project is to clarify the correlation between interfacial structures and functions in the magnetic
multilayers that are the base of the spintronics using the polarized neutron reflectometer SHARAKU (BL17). Inthis fiscal year, we planned to study three subjects; (a) magnetic multilayers of the full Heusler alloy Co2MnSi, (b)the ferromagnetic semiconductor (Ga,Mn)As, and (c) Pt/NiFe magnetic films relating to the spin current
phenomenon. We focus on the subject (a) in this report; however, the other two topics are briefly reported first.
We measured the polarized neutron reflectivity (PNR) of a (Ga0.95Mn0.05)As with the thickness of 50 nm on theGaAs substrate under a magnetic field of 10 kOe at 3 K, and obsreved the ferromagnetic moments whose
magnitude of 0.84 µB per Mn atom. This value is consistent with a result of the magnetization measurement. The
key issue of this study is whether the ferromagnetic moments are homogeneously distributed along the depth
direction from the surface or not. Although our observation suggested the homogeneous distribution, we reserve
this conclusion at the moment because of the unexpected small ferromagnetic moment of this sample. We will
publish the report after the measurements of a new sample that has the expected magnetic moment of 4µB.
We tried to simultaneously measure the PNR and the spin current in the Pt/YIG film. Unfortunately, terminals
for the measurement of the spin current peeled off during cooling down the sample. The terminals were attachedto the sample surface using the electrical conductive paste. We are now discussing the more stable way tomaintain the electric contact between the sample surface and the terminals even in low temperatures. The
measurements will be performed again after the improvement of the way to fix the terminal.
The specimen of the multilayer of Co2MnSi was synthesized on a MgO(001) substrate by Dr. Sakuraba (IMR,Tohoku University). The layer structure is Au(3nm)/Co2MnSi(10nm)/Cr(1.2nm)/Co2MnSi(20nm)/Cr(5nm)/Au(30nm)/Cr(15nm)/MgO substrate. In this trilayer, a strong and anomalous 90 degree coupling of the ferromagnetic
moments of two Co2MnSi layers across the thin Cr layer is suggested by the M-H loop measurements. We
intended to directly observe the 90 degree coupling using the polarized neutron reflectometry.

１．研究成果概要（つづき） Outline of experimental results (continued).
The measurements were performed at the ambient temperature. The PNR was measured under an external
magnetic field of 10 kOe in the sample plane to saturate the magnetization and under a low field of 50 Oe. The
ferromagnetic moments are supposed to have the 90 degree coupling under this low field. Incident neutrons werepolarized by a polarizer before the sample, and the spin state of reflected neutrons is analyzed by a spin analyzer
set between the sample and a detector. Reflectivities at three different glancing angles of 0.2, 0.6, and 1.8 degree
were combined to cover a wide q-range from 0.02 to 2 nm-1.

Fig. 1 Polarized neutron reflectivities of the Co2MnSi trilayer under a high magnetic field (left), and a low field (right).

Figure 1 shows the results of the PNR measurements. The left panel displays the result under the high magnetic
field, and the right one under the low field where the 90 degree coupling is expected. In these figures, four kindsof reflectivity, R++, R+-, R-+, and R--, are shown. The first sign in the subscript is the spin state of the incident
polarized neutrons, and the second one is the spin state of the reflected neutrons. The spin of the incident neutrons
is flipped by the perpendicular components of a net magnetization vector of the sample according to the neutron
spins, and is conserved the direction by the parallel components.The reflectivities with the spin-flip are observed
even in the data under the saturation field where all the ferromagnetic moments should be parallel to the neutron
spin. We are now carefully checking whether this is an intrinsic character or originates in imperfectness of thecalibration of efficiencies of the components likethe polarizer and the analyzer, and the spin flippers.
One of simulations of the 90 degree coupling isshown in Fig. 2. The feature of the profiles of R++,and R-- is qualitatively well reproduced by thesimulation. The profiles of R+-, and R-+ are also
very similar to the experimental result; however,
the absolute values are much higher in thesimulation than those of the experimental data.
Further analysis is now proceeding. The results will
be reported elsewhere.

Fig.2 An example of simulation of the polarized neutronreflectivity profiles with the 90 degree coupling.

必要に応じて、A4 サイズの用紙に続きを記入して下さい。
Please use A4-size papers for further reporting, if necessary.