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Jiro Kitagawa

Publications and source records attributed to Jiro Kitagawa.

26 records · Page 2Linked to original sources

Teaching electromagnetism through demonstration of a practical application involving learning content from multiple disciplines

Teaching electromagnetism by demonstrating a practical application associated with learning content is an important teaching technique. Demonstrations are often performed through video-assisted procedures, and are usually limited to a one-to-one correspondence between the application and the learning content. However, understanding of practical applications frequently requires understanding of learning content beyond the ones studied in electromagnetism. I designed a process to teach the working principles of cryogen-free superconducting magnets. Understanding of this practical application requires students to have knowledge of learning content from the disciplines of electromagnetism and solid state physics. The teaching process involved the use of homemade videos demonstrating magnet operation, which was combined with a flipped classroom and an active learning approach.

physics.ed-ph↗

Superconductivity in oxygen-added Zr5Pt3

Mn5Si3-type structure has been offering an interstitial chemistry. Recent report of enhancement of superconductivity in a Nb-based Mn5Si3-type compound by addition of an interstitial atom motivated us to investigate the effect of oxygen-addition in Mn5Si3-type Zr5Pt3. The superconducting critical temperature of 6.4 K in the parent Zr5Pt3 is monotonously reduced to 3.2 K in Zr5Pt3Ox (x=0.6) with increasing oxygen-content. As x is further increased from 0.6 to 2.5, exceeding the full occupancy of oxygen site (x=1.0), samples become multi-phases composed of Zr5Pt3O0.5-0.6, ZrPt and ZrO2. However, the superconducting critical temperature slightly increases to 4.8 K at x=2.5. The metallographic observation has revealed a change of microstructure at x>=1.0. The change of microstructure and/or the composition effect would be responsible for the enhancement of superconductivity.

cond-mat.supr-con↗

New room-temperature ferromagnet: B-added Pd0.75Mn0.25 alloy

Mn-based room-temperature ferromagnets attract considerable attention due to their high ordered Mn moment. We have found that a Pd0.75Mn0.25 alloy with added B (Pd0.75Mn0.25Bx) shows room-temperature soft ferromagnetism, whereas the parent Pd0.75Mn0.25 alloy is a spin-glass system. The saturated Mn moment at room temperature systematically increases to 2.68\muB/Mn as x increases to 0.125. The maximum Curie temperature of 390 K is also realized at an x of 0.125. The experimental results suggest a tunable soft ferromagnetism, which is governed only by the boron concentration. Our results will pave the way in chemical control of room-temperature bulk ferromagnetism in Mn compounds based on the addition of an atom with a small atomic radius.

cond-mat.mtrl-sci↗

Hill plot focusing on Ce compounds with high magnetic-ordering-temperatures and consequent study of Ce2AuP3

Hill plot is a well-known criterion of the f-electron element interatomic threshold-distance separating the nonmagnetic state from the magnetic one in actinides or lanthanides. We have reinvestigated the Hill plot of Ce compounds using a commercial crystallographic database CRYSTMET, focusing on a relationship between the Ce-Ce distance and the magnetic ordering temperature, because a Ce compound with no other magnetic elements scarcely has a magnetic ordering temperature higher than 20 K. The Hill plot of approximately 730 compounds has revealed that a Ce compound, especially for ferromagnet, showing the high magnetic-ordering-temperature would require a short Ce-Ce distance with a suppression of valence instability of Ce ion. Through the study, we had interest in Ce2AuP3 with the Curie temperature of 31 K. The ferromagnetic nature has been examined by a doping effect, which suggests a possible increase of magnetic anisotropy energy.

cond-mat.mtrl-sci↗

Illumination effect by visible continuous-wave laser on bulk 40 K-superconductors

Visible CW (continuous wave) -laser heating effects on the bulk superconductors CeFeAsO0.65F0.35 and MgB2 with 1.5 mm thickness have been investigated by measuring the temperature dependence of electrical resistivity. Each compound shows a critical-temperature Tc reduction with increasing fluence rate. At the normal state, a parallel circuit model based on the Fourier's law can well reproduce the temperature dependence of electrical resistivity of illuminated sample. On the other hand, the predicted temperature-rise due to the laser heating in the superconducting state is much smaller than the observed Tc-reduction. A temperature gradient of a few K across the sample thickness easily triggers the destruction of bulk superconductivity. Furthermore we have found a slight Tc-enhancement in CeFeAsO0.65F0.35 after a rather high fluence-rate irradiation.

cond-mat.supr-con↗

Optical, transport and magnetic properties of new compound CeCd3P3

We have found that CeCd$_{3}$P$_{3}$ crystallizes into a hexagonal ScAl$_{3}$C$_{3}$-type structure. The optical, transport and magnetic properties of CeCd$_{3}$P$_{3}$ were investigated by measuring the diffuse reflectance, electrical resistivity and magnetization. CeCd$_{3}$P$_{3}$ is a semiconductor with the fundamental band gap of approximately 0.75 eV. The 4$f$ electrons of Ce$^{3+}$ ions are well localized but do not show long range order down to 0.48 K, presumably due to the geometrical frustration of Ce atoms. The magnetic ordering temperature is possibly lower than that of isostructural CeZn$_{3}$P$_{3}$ (0.75 K). Because several $f$-electron compounds with the ScAl$_{3}$C$_{3}$-type structure are quantum spin systems, CeCd$_{3}$P$_{3}$ may be a candidate of quantum spin liquid. On the other hand, the relatively large band gap compared to approximately 0.4 eV in CeZn$_{3}$P$_{3}$, would not be intimate with the observation of photoinduced Kondo effect, providing a potentially new range of applications of devices based on the Kondo effect.

cond-mat.str-el↗

Photoinduced Kondo effect in CeZn$_{3}$P$_{3}$

The Kondo effect, which originates from the screening of a localized magnetic moment by a spin-spin interaction, is widely observed in non-artificial magnetic materials, artificial quantum dots, and carbon nanotubes. In devices based on quantum dots or carbon nanotubes that target quantum information applications, the Kondo effect can be tuned by a gate voltage, a magnetic field, or light. However, the manipulation of the Kondo effect in non-artificial materials has not been thoroughly studied; in particular, the artificial creation of the Kondo effect remains unexplored. Per this subject study, however, a new route for the optical creation of the Kondo effect in the non-artificial material $p$-type semiconductor CeZn$_{3}$P$_{3}$ is presented. The Kondo effect emerges under visible-light illumination of the material by a continuous-wave laser diode and is ultimately revealed by photoinduced electrical resistivity, which clearly exhibits a logarithmic temperature dependency. By contrast, a La-based compound (LaZn$_{3}$P$_{3}$) displays only normal metallic behavior under similar illumination. The photoinduced Kondo effect, which occurs at higher temperatures when compared with the Kondo effect in artificial systems, provides a potential new range of operation for not only quantum information/computation devices but also for operation of magneto-optic devices thereby expanding the range of device applications based on the Kondo effect.

cond-mat.str-el↗

Improved room-temperature-selectivity between Nd and Fe in Nd recovery from Nd-Fe-B magnet

The sustainable society requires the recycling of rare metals. Rare earth Nd is one of rare metals, accompanying huge consumption especially in Nd-Fe-B magnets. Although the wet process using acid is in practical use in the in-plant recycle of sludge, higher selectivity between Nd and Fe at room temperature is desired. We have proposed a pretreatment of corrosion before the dissolution into HCl and the oxalic acid precipitation. The corrosion produces $γ$-FeOOH and a Nd hydroxide, which have high selectivity for HCl solution at room temperature. Nd can be recovered as Mn$_{2}$O$_{3}$-type Nd$_{2}$O$_{3}$. The estimated recovery-ratio of Nd reaches to 97\%.

cond-mat.mtrl-sci↗