実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report

提出日 Date of Report
Jan. 7, 2016

課題番号 Project No.

装置責任者 Name of responsible person

2015A0016

Shin-ichi Itoh

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Magnetic excitations in the spin-3/2 antiferromagnetic alternating

BL12 HRC

chain substance HoCrGeO5

実施日 Date of Experiment

実験責任者名 Name of principal investigator

Nov. 17 to 20, 2015

Masashi Hase所属 Affiliation
National Institute for Materials Science (NIMS)
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.
Holmium chromium germanate, HoCrGeO5, powders and Erbium chromium germanate, 166ErCrGeO5, powders.

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.

An interesting phenomenon in quantum spin systems is the appearance of a spin-singlet ground state with a spingap (singlet - triplet excitation). When the spin value is larger than 1, existence of a spin-singlet ground statewith a spin gap was not confirmed experimentally. We expected antiferromagnetic (AF) alternating spin-3/2
chains of Cr3+ in RCrGeO5 (R = Y or rare earth) [1] and a spin-singlet ground state with a spin gap. We
performed inelastic neutron scattering (INS) experiments on YCrGeO5, 154ErSmCrGeO5, and NdCrGeO5
powders using the HRC spectrometer at BL12 [2]. We observed magnetic excitations of Cr3+ spins and obtainedthe dispersion relation of the magnetic excitations parallel to the spin chain using the conversion method
developed by Tomiyasu et al. [3]. We confirmed experimentally the spin gap. The dispersion relation can be
explained by the AF alternating spin chain model. The energy range of the dispersive first-excited triplet states is
10 to 23 meV and 18 to 23 meV for Y and Sm, respectively.

12. 実験方法及び結果（つづき） Experimental method and results (continued)
The ground state is a dimer state with a strong bond alternation (SD state) and a dimer state with a weak bondalternation (WD state) for 0 ≤ α < 0.41 and 0.41 < α < 1, respectively. Here, α is the ratio of two exchangeinteraction values in the chain. The value of α is 0.14 and 0.05 for Y and Sm, respectively. The ratio depends onrare earth. In order to find RCrGeO5 having a WD state, we performed INS experiments on HoCrGeO5 and166

ErCrGeO5 powders using the HRC spectrometer at BL12. The incident neutron energy Ei was 51.0 or 92.1

meV.
Figure 1(a) shows INS results of HoCrGeO5 powders at 3.8 K using Ei = 51.0 meV. Magnetic excitations areapparent around 13 meV. The Q dependence of the intensity shows a maximum around Q = 1.3Å−1, indicatingthat Cr3+ spins generate the 13 meV excitations. The value of 13 meV corresponds to the spin gap. The 13 meVexcitations remain at high Q. Therefore, crystal-field excitations of Ho (total angular momentum J = 8) may
overlap. We can see excitations around 22 meV that probably correspond to the highest energy of the dispersive
first-excited triplet states. We can see other dispersionless excitations, for example around 34 meV. They may bealso crystal-field excitations of Ho.
Figure 1(b) shows INS results of 166ErCrGeO5 powders at 2.5 K using Ei = 51.0 meV. Magnetic excitations areapparent around 10.5 and 13.5 meV. The Q dependence of the intensity shows a maximum around Q = 1.3Å−1 ,indicating that Cr3+ spins generate the 10.5 and 13.5 meV excitations. These excitations remain at high Q.
Therefore, crystal-field excitations of Er (total angular momentum J = 15/2) may overlap. We can see weakexcitations up to 26 meV that probably correspond to the highest energy of the dispersive first-excited triplet
states. We can see other dispersionless excitations, for example around 33 meV. They may be crystal-field
excitations of Er. We will perform further quantitative analyses.
[1] R. V. Shpanchenko et al., J. Solid State Chem. 181, 2433 (2008).
[2] M. Hase et al., Phys. Rev. B 90, 024416 (2014).
[3] K. Tomiyasu et al., Appl. Phys. Lett. 94, 092502 (2009).

Fig. 1 The INS intensity map in the 𝑄 − 𝜔 plane obtained using 𝐸𝑖 = 51.0 meV. (a) The results ofHoCrGeO5 at 3.8 K. (b) The results of 166ErCrGeO5 at 2.5 K.

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