実験報告書様式（一般利用課題・成果公開利用）（ ※本報告書は英語で記述してください。ただし、産業利用課題として採択されている方は日本語で記述していただいても結構です。 ）MLF Experimental Report

提出日 Date of Report

課題番号 Project No.

装置責任者 Name of responsible person

2014A0197

Toshiya Otomo

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Observation of local lattice distortion causing self-doping effect to half
metallic feromagnet CrO2NOVA (BL21)

実験責任者名 Name of principal investigator

実施日 Date of ExperimentKatsuaki Kodama

2014/4/25-27

所属 Affiliation
Japan Atomic Energy Agency
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.
Powder sample of CrO2 (about 1.7g)

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

The magnetic and transport properties of half metallic ferromagnets CrO2 have been studied as a candidate of
the spintronics materials.

However, an origin of the metallic ferromagnetism in CrO2 remains unsettled. As amechanism of the metallic ferromagnetism in CrO2, self-doping effect has been suggested. [1] In the recent
NMR measurement, two kinds of Cr sites with different magnetic moments are observed, indicating two kinds ofself-doped Cr sites with valences of +4±δ. [2] These results suggest that the self-doped carrier exhibits metallic
ferromagnetism through the double exchange type mechanism. Although this scenario can explain metallicferromagnetism in CrO2, it is not consistent with the reported crystal structure including only single Cr site.
In order to reveal the existence of two kinds of Cr site with different valence due to self-doping effect, we have
perform PDF (atomic pair distribution function) analysis on powder neutron diffraction data of CrO2 obtained byusing NOVA. The diffraction data were collected at 50, 370, 410 and 473 K.

First, we analyze the diffraction

data at 473 K where the compound is in paramagnetic phase (The ferromagnetic transition temperature of CrO2is about 390 K).

Figure 1 shows the diffraction patterns aｔ 473 K and the fitting results by using z-Rietveld.
12. 実験方法及び結果（つづき） Experimental method and results (continued)
In the analysis, the reported tetragonal structure

Fig. 1

with a space group P42/mnm which has a single Crsite is used. The calculated line almost reproduces
the observed diffraction pattern, confirming thatthe averaged structure at 473 K is the tetragonalwith P42/mnm.

In Fig. 2, the atomic pair

distribution function G(r) obtained at 473 K isshown by open circles.

The red line shows thefitting result using the tetragonal structure with

6P42/mnm corresponding with the averaged structure.

observed
fitting for P42/mnmFig. 2

4

Clear discrepancy between the observed and calculated2

distortion which can be detected in the present
experimental accuracy is absent, at least, at 473 K.

G(r) (Å-2)G(r) is not observed, indicating that the local lattice0-2

According to the NMR measurement, the inequivalent
Cr sites have to exist in the ferromagnetic phase. Then-4

we should perform the local structural analysis on the-6

data obtained at 50 K although the PDF analysis in theferromagnetic phase is difficult because of including
magnetic scattering component.
References[1] Korotin et al. Phys. Rev. Lett. 80 (1998) 4305.
[2] Shim et al. Phys. Rev. Lett. 99 (2007) 057209.

223456r (Å)

78910