実験報告書様式（プロジェクト利用）

MLF	
 Experimental Report

提出日 Date of report2014 年 10 月 11 日

実験課題番号 Project No.

装置責任者 Name of responsible person

2013S01

伊藤晋一

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

高分解能チョッパー分光器による物質のダイナミクスの研究

HRC (BL12)

実験責任者名 Name of principal investigator

利用期間 Dates of experiments

伊藤晋一、益田隆嗣*

2013 年 4 月 – 2014 年 3 月

所属 Affiliation
高エネルギー加速器研究機構、東京大学*

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.
1. Introduction

The High Resolution Chopper Spectrometer (HRC) was installed and is being operated at BL12 in MLF,
J-PARC, to study dynamics in condensed matters with high-resolutions and with relatively high-energy
neutrons [1,2], under the framework of the S-type project. This project is aim to establish a comprehensive
picture in condensed matter physics by observing wide range of correlated electron systems using the HRC.
We selected some topics among them and focused on the following two points of view: high energy neutron
studies on dynamical structures in metallic magnets, and, high accuracy studies on novel grounds states inlow dimensional quantum spin systems.
We have optimized the performance of the HRC for this project. The HRC delivers high-resolutions andrelatively high-energy neutrons for a wide range of studies on the dynamics of materials, and we proposed
three types of experiments on the HRC, as indicated in Fig. 1. The first technique targets high-resolution
experiments in a conventional energy momentum space (region A in Fig. 1). This experimental condition isuseful for simultaneously determining a dispersion relation of excitations and details of the dynamical
structure factor. The second technique aims to access the first Brillouin zone by using low-angle detectors
and high-energy neutrons (region B). This is the so-called neutron Brillouin scattering (NBS). Observationof ferromagnetic spin waves from a polycrystalline sample
becomes possible and should be useful for material development.
The third technique opens the possibility of accessing eV region(region C). Dispersive excitations up to a sub-eV energy region
can be observed by using single-crystal samples. Electronic
excitations are expected to be observable, if eV neutrons arepractically utilized.
	  In this report, we describe the construction, and the instrumental
improvements after that, also the scientific results from this initial
operation in the period between JFY2008 and JFY2013. Amongthese activities, in particular, the NBS method has beensuccessfully launched, and demonstrations and results have beenobtained. It should be noted that the HRC was constructed and is
Energy-momentum space
being operated under the collaboration between the Institute for Fig. 1
threetechniquesofSolid State Physics, the University of Tokyo and the Institute of forhigh-resolution experiments A, B, C
Materials Structure Science, High Energy Accelerator Research
proposed for the HRC.
Organization (KEK).
1１．研究成果概要（つづき） Outline of experimental results (continued).

2. Design and Initial Construction
On a chopper spectrometer, a neutron beam is monochromatized by a Fermi chopper and then incident
on a sample to be investigated. The neutrons scattered from the sample are detected by a neutron detector
placed at a certain scattering angle. The energy transfer (E) and momentum transfer (Q) from the neutron to
the sample are determined by measuring the time-of-flight (TOF) and the scattering angle (φ) of thedetected neutron. The Fermi chopper consists of a slit package inserted to a cylinder rotating in
synchronization with the production timing of pulsed neutrons. Neutrons pass through the slit package
when it rotates to a position of the slit parallel to the incident neutron beam, and the slit-open time(chopper-open time) determines the energy resolution of the spectrometer. High energy neutrons from thepulsed neutron source are scattered and moderated within the spectrometer, resulting in a large amount ofbackground noise. A T0 chopper reduces this noise by blocking the incident neutron beamline at aroundtime zero. Also, to increase the neutron flux, a supermirror guide tube is mounted in the primary flight path.
A schematic layout of the HRC is illustrated in Fig. 2. The size parameters are L1 = 15 m (the distance
between the neutron source and the sample), L2 = 4 m (the distance between the sample and the detector),and L3 = 1 m (the distance between the Fermi chopper and the sample). The HRC at BL12 faces thedecoupled moderator, which has an area of 100 mm × 100 mm, and the maximum sample size is assumed
to be 50 mm × 50 mm. In this geometrical condition, the energy resolution is estimated to be ΔE/Ei = 2.5%
(Ei: incident neutron energy) for the optimum condition where the chopper-open time Δtch is equal to thepulse width Δtm, and the incident beam divergence is estimated to be Δφ = 5 mrad. The energy resolution
can be improved when Δtch < Δtm, with a concomitant reduction in the peak neutron intensity. For ΔE/Ei =1%, the peak neutron intensity is 75% of that for the optimum condition, which we consider to be an
acceptable tradeoff.
	  A supermirror guide tube was partially installed in the primary flight path at the shutter section (m = 3)
and at the biological shielding section (m = 3.65), where m is the ratio of the critical wave number for thesupermirror to that for natural nickel. However, the collimator tube without mirrors was installed instead of
the guide tube (m = 4) in the down stream section due to the limited budget. The m values were determinedby the financial budgets provided. The energy dependence of the flux gain of the guide tube was calculatedby McStas, a large gain is expected for the full installation, as shown in Fig. 3.
9m

sampleL3 = 1m

7m

L2' = 5.2m
L1 = 15m

L2 = 4m
beam dump

T0

Fermi
20°

Bulk Shielding
decoupled
moderator

supermirror guide

1.773m

2.8m

Bulk Shielding
124°
3°
-31°

Fig. 2

Schematic layout of HRC.

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.

2

1°

-10°

A T0 chopper [3,4] was installed 9 m from the neutron source. At this position, the beam cross section is
76 mm × 76 mm. The size of the T0 chopper blade is 78 mm × 78 mm, which includes a ±1 mm margin forthe beam cross section. The length of the blade along the beamline is 300 mm, and the blade is made ofInconel X 750, which was chosen for its mechanical strength and radiation properties. When the blade centeris initially centered on the beamline, it takes 408 µs for the blade to be removed from the beam cross section,and this occurs at a 100 Hz rotational frequency and for a 300 mm rotational radius. The rotational axis isparallel to and under the beamline. Under these conditions, the HRC accepts neutrons with energy less than
2.5 eV. The margin of ±1 mm corresponds to a phase-control accuracy of ±5 µs at 100 Hz. We developed aphase control system which reduces the fluctuations in the rotational period down to 1 µs (FWHM: full
width at half maximum) at 100 Hz at an off beam environment. Also, the fluctuations during beam time were
measured to be approximately 3 µs (FWHM) at any rotational frequency. The observed fluctuations meet therequirement demanded by the phase-control accuracy within ±5 µs.
A newly developed Fermi chopper [5] was installed at L3 = 1 m. We tried to develop the Fermi chopperby modifying a turbo molecular pump (TMP) with a magnetic bearing system. First, the TMP blade was
replaced by the slit package, and we could rotate up to 600 Hz by the TMP controller. Next, we tried todesign the phase control system of the Fermi chopper synchronized with the production timing of pulsed
neutrons. We could drive the motor of this system by an external power supply and just by using the TMP
controller as a magnetic bearing controller. Finally, we successfully developed the phase control system.
Based on the developments, we produced the first model of the Fermi chopper made in Japan. The
commercially available composites made of boron fibers were used for the slit materials. In this actual
system, we confirmed the phase control accuracy less than 0.1 µs (FWHM) at 600 Hz against the timing of
the external trigger at an off beam environment. A shifting mechanism of two Fermi choppers was also
developed in order to select one of the choppers or white beam condition.
We mounted 2.8 m (effective length) PSDs (position sensitive detectors) inside the vacuum scatteringchamber. Although it was possible to install detectors at φ = −31° - 124°, the detectors cover at present only
φ = −10° - 42° because of the recent limitations in He3 gas supplies. Therefore, the installed detector area isonly 30% of the entire area. In the main detector area at φ = 3° - 42°, 128 PSDs (effective length: 2.8 m,
diameter: 0.75 inch, He3 gas pressure: 1.8 MPa) were mounted inside the vacuum scattering chamber for
conventional experiments. At low angles (φ = −10° - 1°), 123 shorter PSDs (0.8 m, 0.5 inch, 2 MPa; 0.6 m,
0.5 inch, 2 MPa; 0.6 m, 1 inch, 1 MPa; used at KENS or newly acquired) were mounted; some at L2 = 4 m
and the rest at L2 = 5.2 m at the lowest angles. 20 pieces of the newly acquired PSDs (0.8 m, 0.5 inch, 2MPa) located at around φ = ±0.5° inside the vacuum scattering chamber are used for the NBS experiments.
The PSDs used at KENS were mounted outside the vacuum scattering chamber, facing a thin Al window,of which area is about 1 m2 and thickness is 1.5 mm, on the surface of the vacuum scattering chamber [6].
This size of the window should be designed in consideration of material properties up to the plastic region.
B4C liners were mounted on all the walls inside the vacuum scattering chamber to avoid spurious scattering.
The compositions of particle size of B4C was determined for minimizing water absorption into B4C [7].
The data acquisition (DAQ) system for the HRC is illustrated in Fig. 4 [2]. Signals generated at a PSD are
amplified by preamplifiers and sent to a readout module called NEUNET. When a neutron is captured at a
PSD numbered ndet, the charges generated at both ends of the PSD are digitized and converted to pulse
heights Q1 and Q2 by an analog-to-digital converter (ACD) in the NEUNET where, in an ideal case, theposition u of the detected neutron within the PSD is given by u = LDQ2/(Q1+Q2) with the PSD length LD. A
timing signal from the accelerator defining t = 0 is delivered by a GATENET to NEUNETs and the TOF ofthe detected neutron t is defined. The timing signal is gated by the device status, which is the phasing statusof the choppers, the temperature control status of the sample, etc. Thus, the GATENET forwards the timing
signal to the NEUNETs, only when the device status indicates that all the devices are operational. For
detection of a neutron, the set {ndet, Q1, Q2, t} is generated as an event datum (8 bytes/event) on the NEUNET.
Event data can be accessed through a computer network with SiTCP. In addition, event data from themonitor detectors can be accessed at the GATENET through the computer network with SiTCP. One
NEUNET, which uses the VME standard, controls 8 PSDs. A 19-inch VME rack can contain up to 20
NEUNETs for 160 PSDs. On the HRC, 251 PDSs are controlled by 33 NEUNETs, and a GATENET is also
mounted on the VME rack. The event data are transferred by the computer network from the NEUNETs tothe central processing unit (CPU). We prepared a CPU (POWER MASTER Server A8452 from System
Works Co.) for the DAQ system (DAQ CPU), and installed Scientific Linux 5.4 as well as the DAQ
middleware. Via the DAQ-Middleware, the DAQ-Operator configures the DAQ system and controls3DAQ-Components that control processes in the DAQ system. User commands such as begin/end of the dataacquisition can be sent to the DAQ system through a web-browser user interface.
15
full installpartial (shutter+bioshield)
GAIN

10

5

0
1

10

100
Ei (meV)

1000

Fig. 3Calculated flux gain of the guide tube on
the HRC. In the measurements in Figs. 5 (a) - (c),the guide tube was partially installed (dashed line).

Fig. 4

DAQ system installed on the HRC.

3. Performance
To evaluate the HRC performance, a vanadium standard sample was mounted at the sample position on
the HRC [1]. A monochromatic neutron beam with the Fermi chopper or a white neutron beam without the
Fermi chopper was incident on the sample, and the scattered neutrons were detected with the array of 128
PSDs located at φ = 3° - 42°. A monitor detector was located at 13.4 m from the neutron source (justupstream of the Fermi chopper). The neutron intensities detected by the monitor and that detected by the
PSD array for the white beam are plotted in Figs. 5(a) and 5(b). The observed intensities were in good
agreement with the calculations in the absolute values within a factor. Figure 5(c) shows the elastic scattering
energy spectrum from the vanadium standard sample and detected by the PSD array for the incident neutronenergy of Ei = 203 meV, with the optimum chopper (which provides roughly Δtch = Δtm) at 600 Hz, as afunction of the energy transfer. We chose Ei = 203 meV because the neutron transmission through the
optimum chopper shows a maximum at 200 meV. The solid line is a calculated spectrum without any
adjustable parameters. The energy resolution from the observed energy width was ΔE = 5.2 meV, andtherefore ΔE/Ei = 2.5%. At Ei = 203 meV, the absolute magnitude of the neutron intensity for a
monochromatic beam agreed with the calculation, and also it was confirmed that ΔE/Ei = 2.5% in the energy
resolution as designed for the optimum condition. Assuming the optimum condition (ΔE/Ei = 2.5% with Δtch
= Δtm) for any Ei, the neutron flux for inelastic neutron scattering (INS) experiments at the sample position
with a 1 MW proton beam for full installation of the guide tube is estimated as shown in Fig. 5(d).
4

4

10

1

10

obs

0

10

calc

obs

2

10

calc

1

10

Ei = 203 meV
3 ΔE = 5.2 meV
2

obs
calc

2

2

10

3

10

4

(c) PSD(b) PSD
INTENISTY (n/s/meV)

3

10

IPSD (n/s/meV@120kW)

Imon (n/s/meV@120kW)(a) monitor

FLUX (n/s/cm @1MW)

4

10

1

2
6
10 8
6
4
2
5

10 8
6

-1

10

Fig. 5

0

1

10
100
Ei (meV)

1000

10

1

10
100
Ei (meV)

0
-40

1000

-20
0
20
E = Ei - Ef (meV)40(d) sample position

4

1

10
100
Ei (meV)1000

Neutron intensities at the monitor (a) and at the PSD array (b) for white neutron beam. The dips in the observed
data are caused by the operation of the T0 chopper. (c) Elastic-scattering energy spectrum at PSD array forvanadium standard sample with Ei = 203 meV. (d) Expected neutron flux at sample position for the optimum
condition ΔE/Ei = 2.5% for 1 MW proton beam.

The T0 chopper is a key device to reduce the background noise that originates from high-energy neutrons
emitted during neutron production. Figure 6 (a) shows the TOF spectrum observed at the PSD array from thestandard vanadium sample with the T0 chopper running at the rotational frequency of 100 Hz, and with the44. Improvement in instrumentation

5

1.5

10
(b)
INTENSITY (arb.units)

TRANSMISSION

2.5eV
1.0

0.5

(a)

4

10

3

OFF

10

2

10

1

10

ON (100Hz)
0

0.0
0

1000

2000 3000
TOF (µs)

10

4000

0

2000

4000 6000
TOF (µs)

8000

Fig. 6(a) Background noise reduction formonochromatic neutron beam. The TOF spectra with
operating the T0 chopper at 100 Hz (ON) and without
operation (OFF) are indicated. (b) TOF dependence ofthe transmission at 100 Hz measured with the white
neutron beam.

15

GAIN

T0 chopper off and the blade removed from thebeamline [1]. The sloppy chopper was used as the
Fermi chopper and operated at 600 Hz. Since the slit
width of the sloppy chopper is coarse, the neutron
beam passes through the sloppy chopper every halfturn, then many peaks appear. The neutron energy ofthe peak at TOF = 2000 ms corresponds to 0.5 eV. We
successfully reduced the background noise at neutronenergies near 0.5 eV by two orders of magnitude. This
indicates that INS experiments that require thedetection of very small signals can be conducted on
the HRC. Figure 6 (b) shows the T0 choppertransmission as a function of TOF measured using thestandard vanadium sample and detected at the PSD
array with the white neutron beam. We confirm thatthe transmission recovers below 2.5 eV of the neutronenergy at 100 Hz, as designed. The energy for 50%
transmission at 100 Hz is 10 eV, and then neutrons
with energies up to several eV can be used with only aslight reduction in neutron intensities.
Therefore, we confirmed that the observed neutron
intensities and the resolutions of the HRC in the initialconstruction well agreed with the designed
performance [1].

10

5

0
0
10

1

10

2

10

3

10

4

10

E (meV)

Observed gain of the supermirror guideSince the above initial construction, we have Fig. 7
system on HRC, which is the ratio of the intensity ofcontinuously improved the HRC at many points as scattered neutrons from a vanadium sample detected
described below. In particular, by the installation of at the PSD array from 3° to 42° in the present set-up
the collimator system as well as the full guide tube, the including the newly installed guide tube to that in theprevious set-up.
NBS experiments have been feasible on HRC.
On the primary flight path of L1 = 15 m, thesupermirror guide tube was initially installed in the shutter and the biological-shielding sections of 4.6 m.
After that, the collimator tube in the down stream section was replaced by a supermirror guide tube of 5.2 m[8]. By the present installation, we obtained a great intensity gain by a factor of 3 at Ei = 100 meV and afactor of 5 at Ei = 50 meV in comparison with the previous set-up, as shown in Fig. 7.
A Soller collimator system composed of slits of vertical sheets of Cd with a thickness of 0.1 mm wasinstalled just upstream of the sample, and the collimation can be chosen to be 2.3° and 0.6° automatically [8].
Since there was a huge background noise at low angles, as shown in Fig. 8 (upper), a measurement with anempty can was required. Figure 8 shows excitation spectra in a one-dimensional (1D) antiferromanget,
CsVCl3, measured at T = 20 K. By using the 2.3° collimator, the background at low angles was greatly
reduced and a spectrum from the sample can be obtained without an empty scan, as shown in Fig. 8 (lower).
In the lower angle region, PSDs are installed down to 0.5°. These low angle detectors as well as sub-eV
incident neutrons enable the NBS experiments on the HRC [9]. Figure 9 shows observed spectra from anempty can at φ = 0.64° with Ei = 102 meV. A spread of the direct beam at E = 0 meV and a spurious peak at
E = 5 meV were observed with the collimator with the 0.6° collimation. The direct beam spread waseliminated and the spurious peak was reduced by using the collimator with the 0.3° collimation. The
spurious peak at E = 5 meV, originating from a reflection of the direct beam at a position near the PSDs,
could be successfully eliminated by masking the position with a cadmium plate. Finally, based on thesedevelopments, 2.3° and 0.3° collimators were replaced by 1.5° and 0.2° collimators, respectively.
An experimental control environment was developed to combine the measurements of neutron counts
with the control of devices such as choppers, temperature controllers, goniometers, vacuum system, and soon, as shown in Fig. 10 [8]. The HRC Control Platform was developed and installed on the computer named
DAQ-OP (DAQ operator). The HRC Device Control Software controls the devices as well as the DAQ
middleware (DAQ MW) via the Control LAN through the Platform. The HRC Experiment Control Software

5

100

100

80

80

E (meV)E (meV)

executes a sequence composing begin/end of measurements and controls of devices. At present, almost all
the devices on the HRC can be controlled through this platform and these operations can be connected withthe data acquisition (begin/end of measurements). In order to optimize the computing environment, thecomposition of the computers was improved.

60
40
20
0
0

Fig. 840
20

1

2
q (A-1)

3

4

0
0

1

2
q (A-1)

3

4

Excitation spectrum from CsVCl3 measured with Ei = 102 meV on HRC, for the previous set-up (upper) and thepresent set-up with the 2.3° collimator and the full guide tube (lower). The intensities (color) are normalized by
the number of protons incident to the neutron production target. The noise at low-q has been greatly reduced by
the collimator, also the neutron flux has been increased by the full guide tube.

150
Intensity (counts/h)

60

0.6°
0.3°
0.3° mask

3

100

2

50

1

0
0
-20 -10 0 10 20 -20 -10 0 10 20
E (meV)E (meV)
Fig. 9Background noise at φ = 0.64° for the
0.6°, the 0.3° collimators, and the 0.3° collimatorwith a cadmium mask at the position of the direct
beam hit. The incident neutron energy was selected
to Ei = 102 meV, The same data are plotted in both
figures with different scales for the vertical axes.
The lines are guides to the eye.

Fig. 10
Experimental control environment on the HRC.
PMC, TC, GPIB-ETH represent a pulse motor controller, atemperature controller, a GPIB/Ethernet converter,
respectively. The vacuum system is accessible through the
Gateway server and the FL-net. The incident neutron beam
is controlled by the Fermi chopper and the narrower, and thesample environment such as the temperature and the crystal
angle is controlled. The operation status of the T0 chopper
and the vacuum system is monitored.

We also developed the software to analyze
single crystal sample data as well as powder
sample data. The analyzed data can betransformed to the standard Mslice format for aconvenience of users. Also, the process for thealignment of the sample crystal became very easy. The excitation spectra in the three-dimensional system on
the four-dimensional energy-momentum space can be also measured by rotating the crystal axis of thesample, and visualized.
Initially, we installed two Fermi chopper: one is a so-called sloppy chopper for high intensities and theother is optimized for Ei = 200 meV at 600 Hz with the optimum condition. And therefore, the optimum
condition was realized in the energy range of Ei = 10 – 200 meV. At present, we installed a Fermi chopper
optimized for Ei = 500 meV at 600 Hz, and then the energy range for the optimum resolution of ΔE/Ei = 2.5– 3 % was extended up to Ei = 500 meV [8].
In the initial construction, the sample area was separated from the vacuum scattering area near PSDs witha thin Al foil in the vacuum scattering chamber, and the sample area was evacuated by a small TMP toachieve a high vacuum around the sample area. The TMP was replaced by a cryopump with a pumping speed
6

of 28 m3/s and the Al foil was removed. A gate valve with a diameter of 750 mm was also mounted between
the cryopump and the chamber. A cryopump system is now used for evacuating the vacuum scatteringchamber encompassing the sample and the flight path of the scattered neutrons. After installing this system,
the regeneration process of the cryopump, which is the process to release absorbed molecules, was optimized
and a frequency of the evacuation without the regeneration was greatly reduced.
For conventional INS experiments, 128 pieces of 2.8m PSDs, which are mounted into two detector banks,
covers φ = 3 – 42° at present. PSDs for another two detector banks were purchased, and they will be installedsoon.
64 pieces of 2.8m PSDs are mounted on each detector bank panel of 1.5 m × 3 m with a vacuum flange,
and two panels with PSDs are hold on the vacuum scattering chamber. To remove the panel from the vacuum
chamber, it was necessary to remove the shielding block above the vacuum scattering chamber first, and then,remove the panel by using a crane installed at the experimental hall. At present, we mounted a rail on thevacuum chamber body just above each panel, and the panel can be removed from the chamber along the railby using a hand chain hoist. By using this mechanism, we replaced the damaged PSDs by new ones in amuch easier procedure without removing the shielding.
Since the cadmium slits were successful for the incident beam collimator, an oscillating radial collimator
was manufactured for the collimation of the scattered neutron beam.
The deck connecting the space of BL12 to the mezzanine was constructed. Therefore, the mezzanine in
the 1st experimental hall of MLF was completed. Close to the deck, a chopper maintenance area wasconstructed.
In order to cool the sample down to 4 K stably, a GM-type refrigerator was installed. This refrigerator
shows a good cooling performance by improving the radiation shielding.
A cryomagnet to apply the magnetic field up to 14 T to the sample was designed, manufactured anddelivered. We started the commissioning at the Guide Hall of JRR-3M, and confirmed that it was
successfully operated with the maximum magnetic field of 14 T.
Due to the earthquake disaster on 11 March 2011, some pieces of 2.8m PSDs were damaged and someshieldings were slipped on the HRC. We realigned the beamline, restored the shieldings, replaced thedamaged PSDs with new ones, and confirmed the operations of the choppers, the vacuum system, and theelectronics. After these recovery works, the neutron production target at the MLF received the proton beamin December 2011 and the neutron scattering experiments were started in January 2012.
The vacuum scattering chamber and its vacuum system were installed in 2009. The maintenance for them
was performed in September 2012. The property of the large thin Al window on the surface of the chamber
was also confirmed to be normal.
During the partial mounting of the new PSDs, a vacuum leakage occurred in March 2014. To find theleakage point, all the thin Al windows were removed and replaced by thick plates, because of the safety
regulation. The low angle detectors mounted outside the vacuum were removed. Fortunately, the leakage
points were at the vacuum connections of PSDs, not at the Al windows. At present, although the highvacuum is recovered, the low angle detectors mounted outside the vacuum are still removed. However, thePSDs for the NBS experiments are mounted in the vacuum.
5. Neutron Brillouin Scattering Experiments
5.1 Feasibility of NBS on HRC
On the HRC, the NBS experiments became feasible by reducing the background noise at low scattering
angles down to φ = 0.5°. NBS is the most promising way to observe excitations in the forward direction frompowders, polycrystals, or liquids. Owing to the kinematical constraints of neutron spectroscopy, incident
neutron energy (Ei) in the sub-eV region is necessary for measuring scattering in the meV transferred energy(E) range close to (000), and with a high energy resolution of ΔE/Ei, further, the scattered neutrons need to
be detected at very low scattering angles (φ). Low angle detectors are essential to access the present energy
momentum space. In fact, the region above the dashed line in Fig. 11, which is the envelope of scan loci for
φ = 5° with respect to Ei, can never be accessed using a conventional spectrometer with the lowest scattering
angle of φ = 5°, for instance.First, NBS experiment was performed on the HRC to observe spin waves in apolycrystalline sample of a cubic perovskite, La0.8Sr0.2MnO3, (Curie temperature: TC = 316 K). Magnetic
properties of this material are well elucidated and it has been already reported that spin waves were measured
by using a single crystal sample. Figure 11 shows the dispersion relation of spin waves in La0.8Sr0.2MnO3
measured with Ei = 100 meV, where DE/Ei = 2%. The observed dispersion relations at 6 and 245 K were7

well fitted to E = DQ2, where Q is the scattering vector. The D values were obtained to be 130 ± 13 and 88 ±2 meVÅ2 at 6 and 245 K, respectively. These values are in good agreement with the results (D = 131 and 89
meVÅ2 at 14 and 250K, respectively) obtained by the previous INS experiments using a single crystal.
Therefore, the feasibility of NBS experiments on the HRC was demonstrated [9-11].
5.2 Spin dynamics in metallic ferromagnet SrRuO3Spin waves in a polycrystalline ferromagnet SrRuO3 (TC ~ 160 K) were measured, because a large single
crystal suitable for INS experiments has not yet been synthesized. The measurement was performed at 7 Kwith Ei = 100 meV, and well-defined spin wave peaks were observed. As shown in Fig. 11, the dispersion
relation of spin waves in SrRuO3 was well fitted to E(Q) = Eg + DQ2 with an apparent energy gap Eg [10].
Also, the temperature (T) dependence of D and Eg was investigated. We found that D(T) was almost
independent of T up to TC, and Eg(T) could be related to the anomalous Hall conductivity. These results
might syggest the intermediate electron correlation in SrRuO3 as well as the vital role of magnetic monopoles
in momentum-space as a source of strong Berry curvature originating from the spin-orbit interaction [12].
10

E (meV)

SrRuO3 T= 7 K
La0.8Sr0.2MnO3 T = 6 K
La0.8Sr0.2MnO3 T = 245 K

5

0
0.0

0.1

0.2

0.3

0.4

0.5

-1

Q (Å )
Fig.11
Spin-wave
dispersion
curvesforLa0.8Sr0.2MnO3 and SrRuO3 determined on the
HRC. The solid lines are fitted curves. The dashedline is the upper boundary accessible with aconventional spectrometer with the lowest angle of
φ = 5°.

5.3 Spin waves in permanent magnet Nd2Fe1411B
Nd2Fe14B is a well-known song permanent magnet with TC = 580 K and the saturation magnetization of
1.6 T.	
  At room temperature, all spins are aligned along the c*-axis. Below 130 K the system exhibits a spin
reorientation. Because the unit cell includes four chemical formulae of Nd2Fe14B in a tetragonal lattice,spin-wave branches are expected to be complicated. In a previous INS experiment using a single-crystalline
sample of Nd2Fe1411B, a spin-wave branch was detected only along the c*-axis around (002) at 6 and 295 K[13]. We performed NBS experiments in a Nd2Fe1411B polycrystalline sample at 6 and 300 K with Ei = 257
meV and ΔE = 5.7 meV [11,14]. The observed spin-wave peaks at 300 K were well fitted to Gaussian
scattering functions with widths determined from the resolution, and the peak positions were determined inFig. 13. The observed peak positions were on the dispersion curve along the c*-axis reported in the previous
experiment using a single crystal [13]. No magnetic peaks were observed at 6 K, this result is also consistent
with the reported dispersion at 6 K.
5.4 Phononic excitations in liquid D2O
Phononic excitations in a liquid D2O were measured at 300 K with Ei = 102 meV and ΔE = 2.0 meV [11].
The observed spectra showed excitation peaks and a resolution-limited elastic peak. The excitation peaks
were fitted with a damped harmonic oscillator scattering function convoluted with the instrumental
resolution width multiplied by a temperature factor and the peak positions E(Q) were determined. The
present analysis was identical to that for the previous inelastic neutron scattering experiment [15]. As shownin Fig. 14, the Q dependence of the observed peak positions down to Q = 0.02 Å-1 was well fitted to E(Q) =cQ with c = 21.4 ± 0.2 meVÅ, which is equivalent to c = 3250 ± 30 m/s. The observed sound velocity c was
8

in good agreement with that for the fast sound observed in the previous experiment with Ei = 80 meV and ΔE= 4.8 meV down to Q = 0.035 Å-1 [15].
5.5 Collective dynamics of hydrated β-lactoglobulin
Protein hydration plays a fundamental role in protein behavior: water-protein interactions affect protein
folding, maintain structural integrity, mediate molecular recognition, and accelerate enzymatic catalysis.
Many scattering measurements, both elastic and inelastic, and many molecular dynamics simulations, havebeen performed to investigate the relation between protein dynamics and that of the surrounding solvent
molecules. Single particle dynamics of proteins and hydrated water have been investigated using incoherent
scattering from hydrogen in hydrated protein powder.	
  On the other hand, the investigation of collective
dynamics of proteins and hydrated water using coherent scattering is relatively scarce, although it contains
important information of structure and dynamics. First, we performed NBS experiment of pure D2O at room
temperature on the HRC, as mentioned above. The fast sound mode due to the collective dynamics of water
was detected as well as the inelastic X-ray scattering [16]. Next, hydrated β-lactoglobulin powder wasmeasured at 180 – 298 K. The sample dimension was 40 x 40 x 8 mm3. Figure 15 shows INS signals of thesample at different Q values. The spectra show well-defined acoustic excitations as shoulders (see arrows in
the figure) that change in excitation energy with Q in the low Q region. The dispersion relation observed ininelastic X-ray scattering measurement [17] was found in the present study. The high-frequency soundvelocity obtained from the dispersion relation was almost independent of T and 2460 ± 110 m s-1 at 298 K.
15

20
Nd2Fe1411B

E (meV)E (meV)

10

D2O

15

T = 300 K

5

T = 300 K

10

5

0
0.0

0.1

0.2

0.3

0.4

0.5

0
0.0

-1

Fig. 13
Spin wave dispersion
11
relation of Nd2Fe14 B. The solidline is the dispersion curve along
the c*-axis determined using asingle crystal sample [13].

0.2

0.4

0.6

0.8

1.0

-1

Q (Å )Q (Å )

Fig. 14
Dispersion relation forphononic excitations, the fast sound,in D2O (closed circles). The open
circles are previous results in ref. [15].
The solid line is a fitted line.

S=1
CsNiCl3

6. Experiments in Conventional QE SpaceR = 1.6 ± 0.2

Fig. 15
Inelastic neutron spectraof hydrated β-lactoglobulin at 180 K-1
at (a) Q = 0.25 Å and (b) Q = 0.55
-1
Å .

100

S=3/2
CsVCl3R=1.45±0.27

100

S=3/2
CsVBr3

S=2
CsCrCl3

R=1.24±0.08

30 R=1.15±0.06= 1.37= 1.21= 1.21= 1.14R
R
R
R
6.1 Quantum renormalization effects in 1DHAFs
The ground state of a 1D Heisenberg
5
antiferromagnet (HAF) with S = 1/2, where S is the2050
spin quantum number of magnetic ions, is the50
degenerate singlet spin state (Bethe state). The lowest
10
spin excitations from the Bethe state are renormalized
HRC
INC
INC
MARI
T=20K
T=20K
T=6K
T=25K
from the classical spin-wave state excited from the
κ(T):
κ(T):
Néel state. The excitation energy can be described by
κ(T): INC
κ(T): INC
PRISMA
PRISMA00
0
0
0.0
0.5 0.0
0.5 0.0
0.5 0.0
0.5
E(q) = 4SRJ |sin q| with the exchange constant J, andq(rlu)
the enhancement is defined by the quantum
renormalization factor R; R = p/2 for S = 1/2. On the Fig.16
Dispersion relations of the lowest spinother hand, it is well known that a system with S = 5/2 excitations in 1DHAFs. The solid lines on the data
behaves classically (R=1). Figure 8 shows excitation points (marks) are fitted dispersion curves. The sine
spectrum for CsVCl3 measured on the HRC, where spin curves with bars are those for classical spin waves
excitations were well observed in the entire Brillouin estimated from J determined by κ(T).
zone up to the zone boundary energy and E(q) could be determined as peak positions of spin excitations. To
detect the S-dependent quantum renormalization effect, INS experiments were performed at KENS and ISIS
using 1DHAFs: CsNiCl3 (S = 1), CsVCl3 (S = 3/2), CsVBr3 (S = 3/2), and CsCrCl3 (S = 2). At present, we
improved the data for CsVCl3 on the HRC, also newly analyzed data for the other materials [18]. W emeasured the dynamical structure factor of spin excitations S(q,E) to determine E(q), as shown in Fig. 16. To
determine the value of R, the J value should be obtained. The static spin correlation function S(q) was

E (meV)

QMC

9

QMC

QMC

QMC

80

(b)

(a)

(c)
HRC
LTAS
TAS-1

60

E (meV)deduced by integrating S(q,E) over E, and the inverse
correlation length k was obtained as the width of S(q). The
J value can be determined from κ(T), which is described asa function of J for any S by a quantum theory. In Fig. 16,
the classical dispersion relations estimated by J from κ(T)are also shown with the uncertainties from thedetermination of J. The values of R, which is the ratio ofE(q) at the zone boundary (q = 0.5 rlu) to the classical spinwave energy, were in good agreement with those predictedby quantum Monte Carlo calculations.

5

40

20

0
1

k (rlu)00h (rlu)0
1 0.0

h (rlu)0.5

6.2 Spin waves in ferromagnetic phase of MnPFig. 17
Dispersion relation of spin waves in the
MnP is ferromagnetic below 293 K, and transforms ferromagnetic phase of MnP along the a* (a) and b*
into a helical spin phase at 46 K. In the ferromagnetic axes (b), with calculated curves for acoustic (solid
phase, the easy axis of the magnetization is the c* axis and line) and optical (dashed line) modes. The bars on
the hardest one is the a* axis. In the helical spin phase, the the marks represent statistical errors along the scan
directions. Low energy part along the a* axis isspin rotates in the b*-c* plane with a propagation vector of indicated in (c).
0.117a*. Early INS studies suggested that the helical spin
phase is caused by a delicate balance between exchange interactions [19], also reported that the spin wave
dispersion relation in the ferromagnetic phase can not be described by the conventional q2 law along the a*axis [20].
We determined the spin wave dispersion relations in the ferromagnetic phase at 60 K, by using HRC as
well as LTAS and TAS-1 at JRR-3M [21,22]. The Mn lattice in MnP deviates from a primitive orthorhombic
lattice with displacement parameters u and v along the a and b axes, respectively, and therefore, the unit cell
includes four Mn sites. Since v is negligibly small, the Mn lattice can be approximately divided into two
sub-lattices. We consider an isotropic Heisenberg interaction adding a single ion anisotropy for two
sub-lattices, and take into account of exchange interactions between Mn pairs up to the 6th neighbors. The
observed peak positions of spin waves were well described by this model, as shown in Fig.17.
By using the HRC, spin waves were observed in a wide energy momentum space near to the zone
boundary. In the calculation, the acoustic and optical modes are separated from each other along the a* axis.
Along the b* axis, these two modes resonate with each other at around k = 0.2 rlu (reciprocal lattice unit) andswitch roles, but the two modes are not crossed. Observed spin wave peak positions are well explained by
the two modes. In fact, two spin wave peaks were clearly observed at h = 0.5 rlu on the TAS-1. As shown in
Fig. 17 (c), the low energy part in the a* axis for the presently-improved dispersion relation obtained by the
LTAS was also well fitted to the present model, where the calculated dispersion curve along the a* axis
shows a minimum at around h = 0.14 rlu. This complicated q dependence is caused by the displacement
parameter u, in fact, the minimum disappeared for u = 0.
We successfully observed spin waves in the ferromagnetic phase of MnP along the a* and b* axes in theentire Brillouin zone up to the zone boundary. The dispersion relations were well described by an isotropic
Heisenberg model adding a single ion anisotropy with two sub-lattices, and the anomalous dispersion
relation along the a*-axis was found to be caused by the atomic displacement from the primitive lattice. The
previous studies suggested that the anomalous dispersion is caused by an exchange competition [19] oritinerant nature of d electrons [20]. A recent structural study suggested the existence of the
Dzyaloshinsky-Moria interaction [23]. To resolve these
problems, further investigations are required.
6.3 Mind the “Gap” on quantum spin systems
Quantum spins in a low-dimensional system show
unusual quantum phases such as Haldane gap andspin-Peierls state, by the strong quantum nature. The spin
singlet is the basic starting point for describing a ground stateof the quantum spin chain. Another interest in a quantum spin
systems is the cooperation among physical degrees of
freedoms. The strong correlations between quantum spin andcharge, orbital, and lattice are expected to give rise to afascinating new quantum phase as a realization of high-Tc
10

Fig. 18
Crystal structure of TiOBr. Ti ions (red)are surrounded by boron (yellow) and oxygen(blue) ions, forming quasi two-dimensional plane.

superconductivity in two-dimensional (2D) system. Here, wereport some of research results carried out by using the HRC.
1) Finding the gap in TiOBr: Newly proposed spin-Peierls system
TiOX (X: Cl, Br) has been revealed showing 1D nature associatedwith orbital ordering of Ti ions and super-lattice structure being
related to the Peierls instability. It is pointed out that resulting
only from an arrangement of Ti dxy orbital, the formation of 1D
spin chains and the spin-Peierls transition will be realized.
Recently, it has been demonstrated that TiOBr also exhibits two
successive phase transitions, similar to TiOCl at Tc1 = 27 K and
Tc2 = 47 K. INS experiments were carried out in order to find the
direct evidence of spin-Peierls transition, namely, the spin gap.
The inelastic spectrum with a large amount of poly- crystalline
sample of TiOBr is expected to show the localized signal in thevicinity of the magnetic zone center Q = 0.9 Å-1. This low-Q
access measurement of polycrystalline sample is only achieved bya small angle (φ) and a high incident energy (Ei) condition. The
detectors at around φ = 3° and Ei = 200 meV are used forsearching the excitation at low-Q region. However, obtained
S(Q,E) shows no indication of the existence of magnetic signals
in the spectrum except for phonon contribution. The gap energy
in TiOBr is expected much higher from that measured
thermodynamic properties and by analogy with TiOCl, and could
be 20 meV in energy. It still remains as open questions if thespin-Peierls state under the cooperation of orbital ordering isrealized in this system. The absence of the spin gap implies theground state of TiOBr is not spin singlet state, but is possibly
different state as spin liquid state.
2) Hole dynamics in a 1D spin chain: It is practically hard to
realize the carrier doping in 1D material because the localizationof carriers occurs at low T. We tested spin and hole dynamical
properties in Nd2-xCaxBaNiO5, which is successfully hole doped
1D Haldane system. The	  lightly doped x = 0.035 carrier content
were measured by means of pulsed neutron inelastic scatterin asshown in Fig. 19 [24]. It is clearly observed the entire
one-magnon band with spin gap (Haldane gap) at magnetic zone
center (MZC) addition to intense cystal field excitation of Nd ions.
The zone boundary energy reaches 60 meV that is less comparing
to undoped Haldane chain. On the other hand, the gap slightly
increases in its energy, but still gap opens even holes doped (spincorrelation of Haldane state is known to be spatially exponential).
Moreover, new dynamical structures within the Haldane gap wereobserved upon carrier doping, showing incommensurate
structures centered at MZC. This is originated by the dynamics of
doped-holes. For further experiments, hole carrier dependence of
Ni chain band (Haldane band) and hole dynamics will be focused

Fig. 19 S(Q,E) observed in Nd1.965Ca0.035BaNiO5.

Fig. 20INS
measurements
from(Nd1.30Sr0.70)NiO4 measured on the HRC. (a) - (c)Constant energy slices showing the variation of
the intensity in the (h, k) plane at selectedenergies. The data are averaged over the range
of energies indicated in the figure. (d) Constantenergy cuts along the [-H, H, 0] directions at
various energies. The data are averaged over
(H, H) = (1.0, 1.0) ± (0.1, 0.1). (e) Dispersion of
the magnetic excitations in (Nd1.30Sr0.70)NiO4
along [-H, H, 0] direction.

6.4 Unusual spin dynamics in the checkerboard order in 2D layered nickelate
When the antiferromagnetic insulating phase is melted by carrier doping in the layered transition-metaloxides, the hole doping stabilizes the non- trivial spin-charge ordering towards the metal- insulator transition.
In particular, the doped carriers tend to form the stripe or simple square-lattice checkerboard patterns.
Although the magnetic excitations in the insulating stripe phase can be described by the linear spin-wave
approximation with in-plane anisotropic exchange parameters, a breakdown of the linear spin wave
approximation was observed in the magnetic excitations in the checkerboard phase with higher carrier
concentration. The spin dynamics in the checkerboard phase of (La2-xSrx)NiO4 (x = 0.5) and more metallic(Nd2-xSrx)NiO4 (x = 0.6, 0.7) are systematically investigated by INS experiments using a large single crystals
grown by the floating-zone method. We found that the observed magnetic excitations in the checker- board
phase is qualitatively different from those of the more insulating stripe phase. They do not show behavior of11

counter-propagating spin wave branches up to E ~ 70 meV as shownin Fig. 20, but are rather similar to those in the high Tc cuprates
which show straight-up chimney-like excitations.
6.5 Multiferroic compounds
RFe3(BO3)4 (R=rare earth metal) are a series of multiferroic
compounds that crystallize trigonal structure with three fold screw
chains of FeO6 octahedra and R3+ ions along the crystallographic c
direction. In R = Nd compound easy-plane type Néel order andspontaneous electric polarization appear simultaneously at TN = 30 K.
Weiss temperature is -115 K and the frustration ratio is -3.8. Thus
the compound exhibits multiferroic property as well as the behaviorof frustrated magnet. While magnetic structure was studied in detail[25], magnetic excitation was measured only by using electromagnetic wave including ESR and Raman scattering techniques. INS
experiment to measure the S(q,w) in wide q space is the most Fig. 21 Inelastic neutron scattering
effective method to identify the spin Hamiltonian realized in the spectrum of NdFe3(BO3)4 in case ofcompound. 22 pieces of single crystals are coaligned by X-ray Laue (0,0,L) and (H,0,-1.5).
camera so that a*-c* plane is the scattering plane. Total mass of thesample for INS experiment is 2.1g. T0 chopper is set at 50Hz, 1.5°of collimator is installed in front ofsample, and Fermi chopper, “S”, with 200Hz is used to obtain high neutron flux. GM-type refrigerator wasused to achieve 15 K. The sample was rotated to obtain the 3-dimensional S(q,w). Figure 21 (a) and (b) show
the spectrum cut along (0,0,L) and (H,0,-1.5) directions, respectively. Flat mode at E ~ 1meV is crystal field
excitation of Nd ion, which was consistently observed by ESR and Raman scattering experiment [26,27].
The dispersive modes from collective excitations from Fe spins are observed at 2.5 meV < E < 5.5 meV. The
obtained spectrum was analyzed by the minimal model of Heisenberg Hamiltonian including inchaininteraction and interchain interaction between Fe spins, the interaction between Fe and Nd spins, single ion
anisotropy of Fe spins, and effective mean field at Fe spins. The calculation, indicated by the white curves,
reasonably reproduces the experimental result. We, thus, identified the effective Hamiltonian realized in
NdFe3(BO3)4. The detail will be discussed in the forthcoming publication.
6.6 Experimental confirmation of spin gap in antiferromagnetic alternating spin-3/2 chain substances
RCrGeO5 (R = Y or 154Sm)
One interesting phenomenon in quantum spin systems is the appearance of a spin-singlet ground state
3

YCrGeO5 4.0 K
(a)

2

(b)

I133K-I214K
k =[-0.5, 0.5]

YVO3

Intensity (a.u.)ω (meV)

1

E=
18

0

20
22
24
28

k/π

30

(meV)

Fig. 22
Map of INS intensity in the k-ω plane of
YCrGeO5 at 4.0 K and Ei = 51.1 meV obtained using
the conversion method. The horizontal axis
indicates the normalized wavenumber parallel to thespinchain.
The
white
line
indicates

ω (k) =

212 sin 2 k +10 2 .

(b) The dynamical
structure factor of the AF Heisenberg alternating
spin-3/2 chain ( H = JΣi #$1− (−1)i δ %& Si ⋅ Si+1 with δ =0.75) calculated using the dynamical density-matrix
renormalization group method.

0

2

4
l (r.l.u)

6

Fig. 23
INS spectra in theorbitalorderedphase(133K), subtracted from thatin the orbital disordered
phase(214K).
The
horizontal axis l is the
propagating direction of thepredicted orbital waves.

12

Fig. 24
Contour maps ofintensity in Cs2Cu3SnF12 as afunction of energy and inplane
wave vector for (a) Ei = 81.9 and(b) 21.8 meV. The intensity is
integrated over the wholereachable range of (0,0,L) and(-K,K,0).

with a spin gap (singlet-triplet excitation). When the spin value is larger than 1, existence of a spin-singlet
ground state with a spin gap has not been proved experimentally. We can expect anti- ferromagnetic (AF)alternating spin-3/2 chains of Cr3+ in RCrGeO5 (R = Y or 154Sm) and a spin-singlet ground state with a spin
gap. We performed INS experiments on RCrGeO5 (R = Y or 154Sm) powders to confirm the spin gap
excitations [28]. Excitations are apparent between 8 and 23 meV at 4.0 K in YCrGeO5. Intensities of theexcitations are strong in the small Q range and decrease with increasing T. Therefore, most of excitations aremagnetic excitations. We could confirm a spin gap in the magnetic excitations. Qualitatively the same
behaviors are observed in 154SmCrGeO5. RCrGeO5 (R = Y or 154Sm) are the first spin-3/2 chain substanceshaving a spin gap. Figure 22 (a) shows the map of neutron scattering intensity in the k-ω plane at 4.0 K
obtained using the conversion method developed by Tomiyasu et al. The results correspond to results of asingle crystal measured along the spin chain direction. The intensity is the strongest around k = π as expectedin AF spin chains. The magnetic excitations have a dispersion relation. The white line shows the empiricaldispersion relation of the lowest magnetic excitations and the spin gap is estimated as 10 meV. Figure 22 (b)shows the calculated dynamical structure factors of the AF Heisenberg alternating spin-3/2 chains. The
experimental result agrees well with the calculation.
6.7 Search of orbital waves in YVO3
The orthorhombic perovskite YVO3 shows the G-type orbital ordering in the T range from 77 to 200 K[29]. In this phase, the existence of large orbital fluctuations is suggested [30], and dispersive orbital waves
propagating along the c-axis, due to the 1D spin-orbital correlations, is predicted [31]. In consideration of theneutron scattering cross-section obtained from the correlation function for the orbital angular moment, wehave attempted to detect the orbital waves. Figure 23 shows observed spectra in the orbital ordered phase(133 K), subtracted from those in the orbital disordered phase (214 K). The intensity decreases withincreasing |Q|, where Q = ha*+kb*+lc*, which can be explained by the magnetic form factor for the V3+
orbital. In addition, we found the intensity shows a periodic behavior with the maximum at l = odd number.
This indicates that the observed spectra might be originated from the orbital waves. This experiment was
performed using the fine-resolution Fermi-chopper spectrometer, SEQUOIA at SNS, ORNL, as one of thesubstituted proposals for the disaster of the earthquake on 11 March 2011.
6.8 Kagome lattice antiferromagnet
Geometrical frustrated systems with reduced spatial dimensionality have gathered considerable interest.
They can suppress conventional magnetic orders, and eventually induce novel states of magnetism. Here weconcentrate on Kagome lattice antiferromagnet (KAF), which composes of corner-sharing triangles. Since nocandidate material of KAF with exact lattice geometry and strong two-dimensionality have so far beenreported, low-T magnetism remains to be controversial. There have indeed reported several scenarios todescribe magnetism of KAF in theories. One of intriguing subjects is if the excitation from nonmagnetic
ground state to magnetic excited state is gapfull or gapless. We have recently examined a prominent exampleof S = 1/2 systems, Rb2Cu3SnF12, and revealed the pinwheel valence bond solid ground state. In addition, ananalogue Cs2Cu3SnF12with S = 1/2 is revealed to magnetically order into so-called Q = 0 structure. ThroughINS experiments, we successfully estimated coupling constants of spins. To gain further insight into detailed
view of magnetic excitations of this compound, we performed an INS measurement on the HRC. A single
crystal is mounted on the (HHL) horizontal scattering plane and the (00L) was set to be parallel to theincident neutron beam. We measured spectra at T = 5 K using a CCR with Ei = 81.9 meV. Due to lack ofsample mass and beam intensity, we were unable to obtain conclusive data and only phonon signals wereobserved at high-Q regime (Fig. 24 (a)). Owing to the multi-Ei system of the HRC, however, we succeeded
in detecting magnetic signals spanning G-point (2,2,0) to K-point (5/3,5/3,0) with Ei = 21.8 meV, which isgood accord with recent results of triple-axis and AMATERAS spectrometers (Fig. 24 (b)). We will hereafter
pursue its magnetic origin, and induce quantum critical phenomena by diluting such chemically analogous
systems showing distinct low-T magnetism.
7. Toward eV Neutron Spectroscopy
7.1 Spin density waves in chromium
The spin-density wave (SDW) in Cr is one of the most fascinating subjects in condensed matter physics. It has
a history of long and continuing research. One of the open issues is its magnetic excitation, which arises fromincommensurate magnetic Bragg positions with a steep dispersion slope and extends to more than 600 meV. In
13

order to examine the detailed structure of high-energy magnetic excitations of Cr in (Q,ω) space, we performed
magnetic INS on the HRC using a single crystal with 4 cc in volume. Figure 25 shows an intensity contour map in
the longitudinally-spin- polarized SDW state, where the intensity is projected on (2, k, l) plane over a wide energy
range. Sharp spots appears at three magnetic Γ points: (2, -1, 0) at ω = 250 meV, and (2, 0, ±1) at ω = 150 meV.
The line-cutting profiles along l direction evince that the magnetic cross sections are well localized in Q space. No
consensus has been established yet for this novel high-energy excitation. One scenario is based on spin-wave
excitations from a pseudo localized-spin system with a zone boundary energy of ~1 eV, though Cr is usuallyregarded as a typical itinerant-electron system. Another possibility comes from electron excitations across the
Fermi energy, possibly reflecting the peculiar Fermi surfaces. Further experimental studies toward high-energy
region are required not only to settle such the argument, but also to get a clue to unknown spin dynamics inmetallic magnets.

7.2 Intermultiplet transition in filled skutterudite compound SmFe4P12
Samarium-based filled skutterudite SmFe4P12 was reported to be the first ferromagnetic Kondo- latticecompound. It shows an unconventional heavy-electron state with the large electronic specific-heat coefficient
370 mJ/mol K2 and a ferromagnetic transition at 1.6 K. Although the 4f electrons clearly have a key role in aformation of heavy quasiparticle at low T, there has been lack of basic
information about the 4f electronic states in this system because neutron
scattering experiments on materials containing thermal neutron absorber
elements such as Sm. To avoid this problem, thus we have done INS
experiment on SmFe4P12 by using higher energy neutrons. Figure 26 shows
the INS spectra of polycrystalline SmFe4P12 at 6.5 K and 280 K. The
sample was prepared by using a tin flux method, where natural abundant
Sm isotopes were used. In low Q range, a small peak around 80 ~ 90 meV
is observed at low T. This peak is not visible in high Q range, indicatingthat it is of magnetic origin. If this peak is associated with theintermultiplet transition from J = 5/2 ground state to J = 7/2 multiplet,interestingly, the energy splitting is very small compared to usual
Sm-based compounds. This might originate from the strong c-f
hybridization in filled skutterudite compounds.

8. Summary
We constructed the HRC, since then, we have continuously improved thisspectrometer at many points. We could achieve the best performance of the
14

Fig. 25
Intensity contour onto
(2, k, l) plane with a thickness of
1.9 ≤ h ≤ 2.1. The inset shows aline cut profile along l at (2, -1, 0)
integrating within a range of 1.9 ≤h ≤ 2.1 and -1.1 ≤ k ≤ -0.9.
10x10

-3

SmFe4P12
Ei = 514.1 meVIntensity (arb. units)

8

-1

-1

2Å <Q<6Å
6

T = 6.5 K
T = 280 K

4
2
0

10x10

-3

SmFe4P12
Intensity (arb. units)

7.3 Possibility of observation of electronic	  excitations
The neutron might become a probe observing electronic excitations. It
has been predicted novel magnetic excitations in the halogen bridged
nickel complex, [Ni(chxn)2Br]Br2, which is a 1D charge transfer insulator.
Recently, the 1D extended Hubbard model has been developed fordescribing the physical properties in this system. The optical conductivity
spectrum suggests an interaction of spins to charge excitations. Also, by anangle-resolved photoemission spectroscopy, a clear spin-charge separation
has not been observed in this system, whereas it has been clearly observedin the 1D cuprates such as SrCuO2 and Sr2CuO3. Such behaviors in thisnickel complex might be attributed to a coupling between spin and charge,
because the charge excitation energies are reduced to be comparable to themagnetic excitation energies resulting from reduction of the on-site
Coulomb repulsion via perturbation of the inter-site Coulomb repulsion. As
the result, magnons at low energy region as well as spin-induced charge
excitations at high energy region are predicted [32]. The detection of
spin-induced charge excitations will be a direct experiment adding a newknowledge in physics on the freedoms of spin and charge. However, thisexperiment has not yet been started, because a sizable fully-deuterated
single crystal required for INS experiments has not yet been synthesized.
We are now trying another example.

Ei = 514.1 meV

8

-1

-1

6 Å < Q < 10 Å6

T = 6.5 K
T = 280 K

4
2
0
0

50

100

150

200

Energy (meV)Fig. 26
INS
spectraof
SmFe4P12 at T = 6.5 K and 280
K for (a) momentum transfer-1-1
range of 2 Å < Q < 6 Å and-1-1(b) 6 Å < Q < 10 Å .

HRC in the current technology. It should be noted that the NBS experiments have been feasible on the HRC
by reducing background at low angles as well as increasing the neutron flux, and some results have beenobtained by this technique. In the high resolution experiments in the conventional energy momentum space,
many studies on spin dynamics in materials with current interest in correlated electron systems are in
progress. We have started sub-eV neutron spectroscopy to detect high energy magnetic excitations, and also,
we are planning to observe electronic excitations.
References[1]* S. Itoh, T. Yokoo, S. Satoh, S. Yano, D. Kawana, J. Suzuki and T. J. Sato, Nucl. Instr. Meth. Phys. Res.
A 631 (2011) 90.
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* results from this project.

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