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
2017/1/4

課題番号 Project No.

装置責任者 Name of responsible person

2017A0068

Kaoru Shibata

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Magnetic relaxation in Zn-Ce-Zn single ion magnet

DNA (BL02)

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Maiko Kofu

2017/4/3 – 2017/4/4

所属 Affiliation

2017/6/14 – 2017/6/20

J-PARC Center, JAEA
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.
Nd complex (C40D39NdN8O11S2Zn2)

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.

A single-molecule magnet (SMM) is a metal complex that behaves as an individual nanomagnet. Eachmolecule, containing several metal centers with unpaired electrons, possesses a giant resultant spin. Given
that the giant spin exhibits easy-axis anisotropy (D < 0), the magnetization reversal between the groundstates with Sz = ±S is hindered by the potential barrier of DSz2. The barrier yields a slow relaxation of themagnetization reversal that is characteristic of SMMs. Early SMM researches have focused on the complexes
containing multiple transition metal atoms. During the past decade, lanthanide SMMs have received muchattention as promising materials with high blocking temperature, i.e. stable SMMs [1]. Owing to a large
contribution of angular momentum, lanthanide complexes can become SMMs containing only one or twomagnetic ions. However, the relaxation behaviors of lanthanide SMMs are rather complicated and several
types of mechanisms are discussed, for example Raman, direct and quantum tunneling processes. Clarifying
the mechanism of magnetic relaxation is a key issue in lanthanide SMMs and assists formulation of designing
strategies for engineering long-living SMMs.
12. 実験方法及び結果（つづき） Experimental method and results (continued)
We have first studied a Tb-Cu dinuclear SMM by means of inelastic (INS) and quasielastic neutron scattering(QENS) [2,3]. We are now investigating trinuclear Zn-Ln-Zn complexes (Ln = Ce, Pr, Nd). The system has
only one magnetic center in a molecule, which can be regarded as “single ion magnet”. Interestingly, thecomplexes with Kramers ion (Ce : J=5/2 and Nd : J=9/2) exhibit the SMM behavior while that with nonKramers ion (Pr : J=4) does not [4]. We have performed INS measurements on AMATERAS (2014B0064,201A0094) for these complexes and found that a magnetic excitation is observed at 3-4 meV in the Prcomplex but undetected in the Ce and Nd ones. It indicates that the existence or non-existence of the lowenergy excitation is closely related to whether the ac susceptibility exhibits the non-SMM or SMM behavior.
To investigate magnetic relaxation in the Zn-Ln-Zn SMMs, we have carried out QENS measurements for
the Nd complex using DNA and AMATERAS. Figure 1 (left) displays a QENS spectrum taken at 75 K on theDNA spectrometer. A weak QENS contribution (1 % of elastic intensity) was observed. In fact, we have also
made a xyz polarization analysis using a spin-echo instrument at NIST and confirmed that the fraction ofelastic magnetic scattering is 1.1 ± 0.3 %.
By combining the ac susceptibility data, an overall dynamical map is made as shown in Fig. 1 (right).
Obviously, the relaxation times do not follow the Arrhenius law. So far, the Orbach process through tunnelingbetween pairs of degenerate magnetic sublevels has been considered as a major mechanism for SMMs.
However, (i) the absence of magnetic excitation at 3 meV, corresponding to the potential barrier of 35 K
estimated from ac magnetic susceptibility and (ii) the non-Arrhenius behavior of relaxation time suggest thatthe magnetic relaxation does not take place through the standard Orbach process in the Zn-Ln-Zn SMMs.
Recently, other mechanisms of spin-phonon relaxation including Raman process and an anharmonic phononeffect are much discussed [5,6]. We believe that our study can provide insight into the mechanism ofmagnetization reversal in rare-earth based SMMs.

Fig. 1: (Left) QENS spectrum of Nd complex taken at 75 K using DNA spectrometer. (Right) Arrhenius plotsof relaxation times obtained from QENS and ac susceptibility measurements.
[1] R. Sessoli et al., Coordin. Chem. Rev., 253, 2328 (2013). [2] M. Kofu et al., Phys. Rev. B, 88, 064405 (2013).
[3] M. Kofu et al., Chem. Phys., 427, 147-152 (2013). [4] C. Takehara et al., Dalton Trans., 44, 18276 (2015).
[5] Y. Rechkemmer et al., Nat Commun, 7, 10467 (2016). [6] A Lunghi et al., Nat Commun, 8, 14620 (2017).
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