Superconductor Science and Technology

LETTER • OPEN ACCESS

Experimental realization of a hybrid trapped field magnet lens using a
GdBaCuO magnetic lens and MgB2 bulk cylinder
To cite this article: Sora Namba et al 2019 Supercond. Sci. Technol. 32 12LT03

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Superconductor Science and Technology
Supercond. Sci. Technol. 32 (2019) 12LT03 (7pp)

https://doi.org/10.1088/1361-6668/ab5048

LetterExperimental realization of a hybrid trapped
ﬁeld magnet lens using a GdBaCuO
magnetic lens and MgB2 bulk cylinder
Sora Namba1,3 , Hiroyuki Fujishiro1 , Tomoyuki Naito1 ,Mark D Ainslie2 and Keita Takahashi1
1Department of Physical Science and Materials Engineering, Faculty of Science and Engineering, Iwate
University, 4-3-5 Ueda, Morioka 020-8551, Japan2
Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, United
KingdomE-mail: g0318128@iwate-u.ac.jp
Received 13 August 2019, revised 13 October 2019
Accepted for publication 18 October 2019
Published 5 November 2019
Abstract

A hybrid trapped ﬁeld magnet lens (HTFML) is a promising device that is able to concentrate amagnetic ﬁeld higher than the applied ﬁeld continuously, even after removing an external ﬁeld,
which was conceptually proposed by the authors in 2018. This paper presents, for the ﬁrst time,the experimental realization of the HTFML using a GdBaCuO magnetic lens and MgB2 trapped
ﬁeld magnet cylinder. A maximum concentrated magnetic ﬁeld of Bc=3.55 T was achieved at
the central bore of the HTFML after removing an applied ﬁeld of Bapp=2.0 T at T=20 K. For
higher Bapp, the Bc value was not enhanced because of a weakened lens effect due to magnetic
ﬂux penetration into the bulk GdBaCuO material comprising the lens. The enhancement of thetrapped ﬁeld using such an HTFML for the present experimental setup is discussed in detail.
Keywords: hybrid trapped magnet ﬁeld lens, bulk superconductors, trapped ﬁeld magnets,
magnetic lens, vortex pinning effect, magnetic shielding effect(Some ﬁgures may appear in colour only in the online journal)
trapped by the strong ‘vortex pinning effect’, are usuallymagnetized by ﬁeld-cooled magnetization (FCM) using ahigh, stationary magnetic ﬁeld, for which a magnetic ﬁeld
nearly the same or slightly lower than the applied ﬁeld can betrapped. The trapped ﬁeld capability of such bulks, as estimated from state-of-the-art Jc(B, T) characteristics could
exceed 20 T at 20 K in a disk bulk pair [4]. However, thetrapped ﬁeld is limited experimentally by the poor mechanicalstrength of the brittle ceramic material [5]. A large Lorentz
force is developed in the bulk during the magnetization process, which sometimes results in crack formation and propagation, leading to eventual mechanical failure [6, 7]. To
date, REBaCuO disk bulks have trapped magnetic ﬁelds over
17 T by mechanical reinforcement using glass ﬁber reinforced
epoxy resin or shrink-ﬁt stainless steel to reduce the

1. Introduction
Trapped ﬁeld magnets (TFMs) using superconducting bulks
such as REBaCuO (RE: a rare earth element or Y) and MgB2
have been vigorously investigated for various practicalapplications; for example, rotating machines, magnetic
separation, ﬂywheel energy storage systems and so on [1–3].
Superconducting bulk TFMs, in which magnetic ﬂux is3

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Supercond. Sci. Technol. 32 (2019) 12LT03

Figure 1. (a) Cross-sectional view of the schematic illustration of the experimental setup for the HTFML on the cold stage of a refrigerator.
(b) Cross-sectional and top views of the GdBaCuO magnetic lens with slits. When a magnetic ﬁeld is applied along the +z-axis direction to
the GdBaCuO magnetic lens, the magnetic ﬁeld penetrates from the slits and the shielding current ﬂows as shown by the red arrows. As aresult, the magnetic ﬁeld increases along the +z-direction due to the shielding current.

electromagnetic hoop stress [4, 8]. A ring-shaped bulk
superconductor that can produce uniform, high magnetic
ﬁelds within the central bore is a strong candidate for compact
cryogen-free nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) systems [9–11]. The 1H spectraof toluene with a full width at half maximum of 0.4 ppm(80 Hz) was achieved in the 10 mm room temperature bore in
the bulk NMR [10]. The ﬁrst MRIs using annular EuBaCuO
bulks were also reported with a magnetic homogeneity of
37 ppm (peak-to-peak) achieved in a Φ 6.2 mm×9.1 mm
cylindrical space with ﬁrst order shimming [11]. Using thissystem, a clear 3D image of a chemically-ﬁxed mouse fetus
was acquired.
On the other hand, a ‘magnetic lens’ using cone-shaped
superconducting bulks has been investigated, in which amagnetic ﬁeld is concentrated in the bore of the lens using the‘diamagnetic shielding effect’ of superconducting materials
and the available magnetic ﬁeld in the lens is higher than theapplied ﬁeld generated by an external magnetizing coil
[12–18]. For example, a concentrated ﬁeld of Bc=12.42 T
has been achieved at 20 K for a background ﬁeld of
Bapp=8 T using a bulk GdBaCuO magnetic lens [12]. Since
the magnetic lens effect vanishes after the applied ﬁeld
decreased to zero, the external magnet must be operated
continuously, which consumes energy and is not environmentally friendly.
We recently proposed a new concept of a hybrid trapped
ﬁeld magnet lens (HTFML) [19], consisting of a cylindricalbulk TFM exploiting the ‘vortex pinning effect’, combinedwith a bulk magnetic lens exploiting the ‘diamagnetic
shielding effect’. Using numerical simulations, the HTFML
was shown to be able to reliably generate a magnetic ﬁeld in
the central bore of the magnetic lens that is higher than boththe trapped ﬁeld in the single cylindrical bulk TFM and theexternal magnetizing ﬁeld, even after the externally appliedﬁeld decreases to zero. For a REBaCuO magnetic lens and
MgB2 TFM cylinder, the HTFML could reliably generate aconcentrated magnetic ﬁeld of Bc=4.73 T with an external
magnetizing ﬁeld Bapp=3 T. For an HTFML comprised of
REBaCuO bulks for both magnetic lens and TFM cylinder, aconcentrated magnetic ﬁeld of Bc=13.49 T could be generated with an external magnetizing ﬁeld Bapp=10 T, where
the temperature of both parts is controlled independently [19].
In addition, the shape of the magnetic lens in the HTFML has
been optimized, and the mechanical stress in the cylinder andlens parts has also been estimated during the magnetizing
process [20].
In this paper, we present, for the ﬁrst time, the experimental realization of the HTFML using a GdBaCuO magnetic lens and MgB2 TFM cylinder, based on the samemagnetizing procedure proposed in [19]. The experimental
results are compared with the simulated ones and enhancement of the Bc value in HTFML is discussed in detail.

2. Experimental procedure
2.1. Experimental setup

Figure 1(a) shows the schematic cross-section of the experimental setup of the HTFML on the cold stage of a refrigerator. The MgB2 cylindrical bulk (60 mm in outer diameter(OD), 40 mm in inner diameter (ID), and 60 mm in height(H)) was fabricated using the inﬁltration method by Experiments Projects Constructions S. R. I., Italy [21, 22].
Figure 1(b) shows the cross-section and top view of the
GdBaCuO magnetic lens. The GdBaCuO magnetic lens was
prepared by the following process: stacked GdBaCuO
cylindrical bulks (OD=36 mm, ID=10 mm, H=30 mm),fabricated using the QMG™ method by Nippon Steel Corporation, Japan [23, 24], were machined into a cone-shape of
OD=30 mm, ID=10 mm, ID2=26 mm, outer height(OH)=30 mm and inner height (IH)=8.0 mm, as shown inﬁgure 1(b). The dimensions of the bulk magnetic lens were2

Supercond. Sci. Technol. 32 (2019) 12LT03

optimized using numerical simulations [20]. Thin slits ofwidth 200 μm was made to disrupt the circumferential ﬂow of
the shielding current during the zero-ﬁeld-cooling (ZFC)
process, which plays an important role in magnetic ﬂux
concentration for the magnetic lens [19]. When an external
magnetic ﬁeld is applied along the +z-axis direction to the
GdBaCuO magnetic lens, the same magnetic ﬁeld penetrates
into the central bore from the slits. The shielding current
ﬂows as shown by the red arrows in ﬁgure 1(b) and an
additional magnetic ﬁeld exists along the +z-axis direction,
mainly due to the counterclockwise shielding current nearest
to the central bore. As a result, the magnetic ﬁeld is enhanced
along the +z-axis direction, which is then higher than theapplied ﬁeld.
The GdBaCuO magnetic lens was encapsulated in astainless steel (SS) holder to prevent fracture of the bulk due
to the large Lorentz force during the magnetization process,and was connected thermally to the cold stage of the refrigerator. The MgB2 cylindrical bulk was reinforced by a SS
cylinder (ID=60 mm, OD=66 mm and H=60 mm) andthe top SS plate (ID=36 mm, OD=66 mm andH=3 mm), which were effective in preventing mechanicalfracture [25, 26]. These SS holders apply a compressive stressto the bulk cylinder and bulk lens during the cooling processfrom room temperature to the operating temperature (e.g.
20 K) due to the difference in the coefﬁcient of thermal
expansion between SS and the bulk superconducting materials. Two CERNOX™ thermometers were attached for monitoring the temperature of the HTFML; one was mounted
directly on the top surface of the MgB2 cylinder, and the otherwas placed on the top surface of the SS holder of the
GdBaCuO lens. Thin indium sheets were inserted between thebulks and the cold stage of the refrigerator (or SS holder) toobtain good thermal contact. The temperature of the cold
stage was controlled using a Pt-Co thermometer and a resistive heater, attached to bottom surface of the cold stage. The
concentrated ﬁeld, Bc, was measured in the central bore of the
HTFML by an axial-type Hall sensor (F W Bell, BHA-921).
The HTFML device was placed in a vacuum chamber andthen evacuated by a vacuum pump system.

Figure 2. Time step (TS) sequence of the external ﬁeld (black: left

vertical axis), Bex, at the center of the HTFML and the operating
temperature (red: right vertical axis), T, during the magnetizing
process to realize the HTFML. The magnetizing applied ﬁeld, Bapp,corresponds to the maximum value of Bex.

(1) The external magnetic ﬁeld, Bex, was ramped up
linearly at +0.222 T min−1 to Bapp=1−3 T over ﬁve
steps, where TS of the ascending stage is deﬁned asTS=1–5. This process corresponds to ZFC magnetization of the GdBaCuO lens, in which the magnetic
ﬁeld at the center is essentially higher than Bapp becauseof the shielding effect by the magnetic lens.
(2) The temperatures of both the MgB2 cylinder and
GdBaCuO lens were decreased to T=20 K under theapplied ﬁeld Bapp, with both materials now in the
superconducting state.
(3) Bex was decreased linearly at −0.011 T min−1 over ﬁve
steps (TS=6–10) down to zero. During this process,the MgB2 cylinder was magnetized by FCM andmagnetic ﬂux was trapped in the cylinder. A magnetic
ﬁeld at the center of the magnetic lens still remains dueto the existence of the trapped ﬁeld in the MgB2
cylinder. As a result, the HTFML can reliably generatea magnetic ﬁeld higher than the trapped ﬁeld in the
single MgB2 TFM cylinder and Bapp, even after
Bex=0.
Prior to the HTFML experiments, the trapped ﬁeld
properties of the MgB2 cylinder and the magnetic concentration capability of the GdBaCuO lens were investigatedindependently using the same time sequence as shown inﬁgure 2 under the external magnetic ﬁeld of Bapp=1−3 T, inwhich either the MgB2 cylinder or GdBaCuO lens was set on
the cold stage.

2.2. Magnetization procedure

Figure 2 shows the time sequence of the external ﬁeld (leftvertical axis), Bex, at the center of the HTFML and theoperating temperature (right vertical axis), T, during themagnetizing process of the HTFML. The magnetizing external ﬁeld, Bapp, corresponds to the maximum value of Bex. The
HTFML device set in the vacuum chamber was inserted into a
cryocooled 10 T superconducting solenoid magnet (JASTEC
JMTD-10T100). First, the MgB2 bulk cylinder and GdBaCuO
bulk lens were cooled to T=40 K. In this stage, the MgB2
cylinder is in the normal state and the GdBaCuO lens is in the
superconducting state, where the time step (TS) is deﬁned asTS=0. The proof-of-concept experiments of the HTFML
were performed according to the following magnetizing
process.

3. Results and discussion
3.1. Trapped field capability of the single MgB2 cylinder

To conﬁrm the trapped ﬁeld capability of MgB2 cylinder, thetrapped ﬁeld properties of the single MgB2 cylinder wasmeasured. Figure 3(a) shows the time evolution of theexternal ﬁeld, Bex, and trapped ﬁeld, Bc, at the center of thesingle MgB2 cylinder during the same time sequence shown3

Supercond. Sci. Technol. 32 (2019) 12LT03

Figure 4. Time step (TS) dependence of the measured magnetic ﬁeld,
Bc, at the center of the single MgB2 cylinder during themagnetization process for applied ﬁelds Bapp=1.0–3.0 T.

Figure 3. Time evolution of (a) the measured magnetic ﬁeld, Bc, atthe center of the single MgB2 cylinder and external ﬁeld, Bex, and (b)the temperatures of MgB2 cylinder and cold stage during themagnetization process for an applied ﬁeld of Bapp=2.0 T.

in ﬁgure 2 under an external magnetic ﬁeld of Bapp=2.0 T.
Figure 3(b) shows the time evolution of the temperatures of
the cold stage and the MgB2 cylinder for the same process. In
the ascending stage, the magnetic ﬁeld, Bc, increased linearlywith increasing Bex and the magnitude of Bc was the same as
the external ﬁeld (Bc=Bex=2.0 T) because the MgB2
cylinder was in normal state (T=40 K). In the descending
stage, after cooling to 20 K, the Bex was slowly decreased at aconstant rate of −0.011 T min−1 and the FCM process was
performed for the MgB2 cylinder. As a result, a trapped ﬁeld
remained of Bc=2.0 T after Bex was decreased to zero due tothe conventional vortex pinning effect. In ﬁgure 3(b), thetemperature of the MgB2 cylinder was nearly the same as thatof the cold stage because of the good thermal contact.
Figure 4 shows the TS dependence of the trapped ﬁeld,
Bc, at the center of the single MgB2 cylinder under external
magnetic ﬁelds of Bapp=1−3 T. In the ascending stage fromTS=0 to 5, the magnetic ﬁeld increases linearly withincreasing TS and the magnitude is the same as the externalﬁeld because the MgB2 cylinder is in normal state. In thedescending stage of the FCM process, for the applied ﬁelds ofBapp=1.0 and 2.0 T, trapped ﬁelds of 1.00 T and 1.98 T,
respectively, were achieved at TS=10 without ﬂux creep.
On the other hand, for higher applied ﬁelds of 2.5 and 3.0 T,
the TS dependence of Bc after TS=5 gradually decreased
and the ﬁnal trapped ﬁeld was 2.18 T, which suggests the
maximum trapped ﬁeld capability of the MgB2 cylinder atT=20 K. The trapped ﬁeld cannot increase over 2.18 T, even
if applied ﬁeld is higher than 3.0 T. In the conceptual paper[19], Bc=2.85 T was predicted at the ﬁnal step at T=20 K
in the bore of MgB2 cylinder for Bapp=3.09 T. The lower Bc

Figure 5. Time evolution of (a) the measured magnetic ﬁeld, Bc, atthe center of the single GdBaCuO bulk lens and external ﬁeld, Bex,and (b) the temperatures of GdBaCuO bulk lens and cold stage
during the magnetization process for an applied ﬁeld of
Bapp=2.0 T.

value in the present experiment results from the lower Jc(B, T)of the present MgB2 cylinder, compared with that used in thesimulations in [19].
3.2. Magnetic shielding capability of the single GdBaCuO
bulk lens

The magnetic shielding capability of the GdBaCuO bulk lens
was measured using the single GdBaCuO bulk lens during theZFC process. Figure 5(a) shows the time evolution of themagnetic ﬁeld, Bc, at the center of the single GdBaCuO bulk
4Supercond. Sci. Technol. 32 (2019) 12LT03

Figure 6. TS dependence of the measured magnetic ﬁeld, Bc, at thecenter of the single GdBaCuO magnetic lens during the magnetization process under applied ﬁelds, Bapp=1.0–3.0 T. For TS=10,
the Bc value increased negatively with increasing Bapp.

Figure 7. Time evolution of (a) the measured magnetic ﬁeld, Bc, atthe center of the HTFML and external ﬁeld, Bex, and (b) thetemperatures for each measurement point during the magnetizing
process for Bapp=2.0 T.

lens and the external ﬁeld, Bex, during the same time sequence
shown in ﬁgure 2, under an external magnetic ﬁeld of
Bapp=2.0 T. Figure 5(b) shows the time evolution of thetemperatures of GdBaCuO bulk lens and the cold stage under
the same process. In the ascending stage, a clear magnetic
ﬁeld concentration was observed; Bc=3.76 T was achieved,
which resulted in a magnetic ﬁeld concentration ratio of
Bc/Bapp=1.88. A temperature rise of about 2.1 K took place
during ascending stage from 0 to 10 min, originating frommagnetic ﬂux penetration into the magnetic lens. When thetemperature of the cold stage was set to 20 K, the minimum
temperature of the GdBaCuO bulk lens encapsulated by the
SS holder was only 26.5 K, which may come from animperfect thermal contact between the bulk lens and the SS
holder. It should be noted that the ﬁnal Bc value was not zero,
but a negative one of −0.48 T. This result suggests that somemagnetic ﬂux penetrated into the surface of the bulk lens anda residual magnetic ﬁeld along the –z-direction existed due tothe vortex pinning effect.
Figure 6 shows the TS dependence of the magnetic ﬁeld,
Bc, at the center of the single GdBaCuO bulk lens during theZFC process under applied magnetic ﬁelds ofBapp=1.0−3.0 T. In the ascending stage from TS=0 to 5,
the magnetic ﬁeld was concentrated by the shielding current.
For lower Bapp=1 and 2 T, Bc=2.04 and 3.76 wereachieved at TS=5, which correspond to magnetic ﬁeld
concentration ratios, Bc/Bapp, of 2.04 and 1.88, respectively.
The Bc values increased for higher Bapp, which were 4.55 T
and 5.19 T for Bapp=2.5 and 3.0 T at TS=5, respectively.
However, the magnetic ﬁeld concentration ratio, Bc/Bapp,
gradually decreased due to increased magnetic ﬂux penetration into the bulk lens. For the ﬁnal stage (TS=10), at which
the external ﬁeld was zero, the Bc value increased negatively
with increasing Bapp for the same reason. For all the cases, theminimum temperature of the GdBaCuO bulk lens encapsulated by the SS holder was only 26.5 K. To improve theperformance of the magnetic lens, lowering its temperature isnecessary.

3.3. Realization of the HTFML

Finally, we present the experimental realization of the
HTFML using GdBaCuO magnetic lens, combined with the
MgB2 bulk cylinder. Figure 7(a) shows the time evolution of
the magnetic ﬁeld, Bc, at the center of the HTFML during themagnetizing process shown in ﬁgure 2 under an external
magnetic ﬁeld of Bapp=2.0 T. Figure 7(b) shows the time
evolution of the temperatures measured at each position. In
the ascending stage, the Bc value reached 3.65 T and thenslightly decreased to 3.55 T at the end of the descending stage
due to ﬂux ﬂow. The magnetic ﬁeld concentration ratio,
Bc/Bapp, was 1.76 at the end of the ramp. The temperatures ofthe MgB2 cylinder and the GdBaCuO bulk lens on the SS
holder were 20.0 and 26.5 K, respectively. These results
demonstrate the HTFML effect experimentally for theﬁrst time.
Figure 8 shows the TS dependence of the magnetic ﬁeld,
Bc, at the center of the HTFML during the magnetizing process under applied ﬁelds of Bapp=1.0–3.0 T. At the end of
the ascending stage (TS=5), the Bc value for each Bapp wasnearly the same as that for the single GdBaCuO magnetic lenscase, as shown in ﬁgure 6. In the descending stage, for
Bapp=1.0 and 2.0 T, the Bc value was nearly the same as thatat TS=5. On the other hand, for Bapp=2.5 and 3.0 T, the Bc
value gradually decreases with increasing TS. As a result, theﬁnal Bc value for Bapp=2.5 and 3.0 T was smaller than thatfor Bapp=2.0 T. The concentrated magnetic ﬁeld, Bc, at
5Supercond. Sci. Technol. 32 (2019) 12LT03

bore (e.g. 100 mm in ID) has become more readily available
in the science and engineering research communities outsideof the ﬁeld of superconductivity. Thus, building on theseﬁndings, we aim to provide easily a concentrated magnetic
ﬁeld higher than 10 T in an open space using this HTFML
system.

4. Conclusion
We have presented, for the ﬁrst time, the experimental realization of a HTFML, based on the device design and magnetizing procedure recently proposed in [19, 20]. The
important results and conclusions in this study are summarized as follows.
Figure 8. TS dependence of the measured magnetic ﬁeld, Bc, at thecenter of the HTFML device during the magnetization process undervarious applied ﬁelds, Bapp=1.0–3.0 T.

(1) The HTFML effect was demonstrated experimentallyusing GdBaCuO magnetic lens and MgB2 TFM
cylinder for the ﬁrst time, such that a magnetic ﬁeld
can be generated in the central bore of the magnetic lensthat is higher than both the trapped ﬁeld in the single
cylindrical bulk TFM and the external magnetizing
ﬁeld, even after the externally applied ﬁeld decreases
to zero.
(2) A maximum concentrated magnetic ﬁeld of
Bc=3.55 T was achieved in the central bore of the
HTFML device after removing an applied ﬁeld of
Bapp=2.0 T at T=20 K. The maximum Bc value wassmaller than the one estimated by numerical simulations, which results from the lower Jc (B, T) and higher
operating temperature, compared with those of thenumerical predictions.
(3) For higher Bapp, the Bc value was not enhanced becauseof a weakened lens effect due to magnetic ﬂux
penetration into the bulk GdBaCuO material comprising the lens. To enhance the HTFML effect, improving
the thermal contact between the HTFML and the cold
stage and lowering temperature of the GdBaCuO lensand MgB2 TFM cylinder is necessary for the present
setup.

Table 1. Concentrated magnetic ﬁeld, Bc, at TS=5 and 10 at thecenter of the HTFML, and calculated magnetic ﬁeld concentration
ratio, Bc/Bapp for various applied magnetic ﬁelds, Bapp.

Bapp (T)
1.0
2.0
2.5
3.0

Bc (T)
at TS=5

Bc (T)
at TS=10

Bc/Bapp
at TS=10

2.00
3.65
4.45
5.19

1.99
3.55
3.46
3.22

1.99
1.76
1.38
1.07

TS=5 and 10 at the center of the HTFML, and calculated
magnetic ﬁeld concentration ratio, Bc/Bapp, for the various
applied magnetic ﬁelds, Bapp, are summarized in table 1. A
maximum Bc value of 3.55 T was achieved for Bapp=2.0 T.
In the concept paper, in which the HTFML was proposed
to be constructed using a REBaCuO magnetic lens and MgB2
TFM cylinder, a concentrated magnetic ﬁeld Bc=4.73 T was
predicted for an external magnetizing ﬁeld Bapp=3 T using
numerical simulations [19]. However, the maximum Bc value
was as low as 3.55 T experimentally under the same magnetizing process for Bapp=2.0 T. This difference occurs forthe following reasons. Firstly, the assumed Jc (B, T) characteristics of the MgB2 and GdBaCuO bulks used in thesimulations were higher than those of the actual bulks used in
the experiments. Secondly, the minimum temperature of the
GdBaCuO bulk lens was only 26.5 K, when the temperatureof the cold stage was set to 20.0 K. To enhance the HTFML
effect for the present MgB2 cylinder and GdBaCuO bulk lens,
the thermal contact between the GdBaCuO bulk lens and the
SS holder must be improved. Nevertheless, we have realized
the HTFML effect experimentally for the ﬁrst time. Our ﬁnal
goal is to build and test an HTFML using a GdBaCuO
cylinder and GdBaCuO lens, for which a Bc value in excess of
10 T (e.g. Bc=13.5 T [19]) is predicted for a magnetizing
process with Bapp=10 T. A cryocooled 10 T superconducting solenoid magnet with a large room temperature

Acknowledgments
The authors thank Mr Y Yanagi of IMRA Material R&D Co.,
Ltd, Japan, and Dr G Giunchi of Materials Science Consultant, Italy, for their valuable experimental supports. This
research is supported by Adaptable and Seamless Technology
transfer Program through Target-driven R&D (A-STEP) fromJapan Science and Technology Agency (JST), Grant No.
VP30218088419 and by JSPS KAKENHI Grant No.
19K05240. M D Ainslie would like to acknowledge ﬁnancial
support from an Engineering and Physical Sciences ResearchCouncil (EPSRC) Early Career Fellowship, EP/P020313/1.
All data are provided in full in the results section of thispaper.
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ORCID iDs
Sora Namba https://orcid.org/0000-0001-7268-5326
Hiroyuki Fujishiro https://orcid.org/0000-00031483-835X
Tomoyuki Naito https://orcid.org/0000-0001-7594-3466
Mark D Ainslie https://orcid.org/0000-0003-0466-3680
Keita Takahashi https://orcid.org/0000-0002-8278-2688

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