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Hirofumi Wada Last modified date:2019.05.20

Professor / Condensed Matter Physics
Department of Physics
Faculty of Sciences


Graduate School
Undergraduate School
Other Organization
Administration Post
Dean of the Faculty of Sciences
Dean of the Graduate School of Sciences
Dean of the School of Sciences


E-Mail
Homepage
http://pom.phys.kyushu-u.ac.jp/
Academic Degree
Dr. Eng.
Country of degree conferring institution (Overseas)
No
Field of Specialization
Magnetism
Total Priod of education and research career in the foreign country
01years02months
Outline Activities
We study the magnetic, structural, thermal, and electrical properties of metallic materials, which show various exotic phase transitions, such as itinerant electron metamagnetism of transition-metal compounds, valence instability of rare-earth compounds, and unconventional superconductivity. Currently, we are focusing on electrical transport properties in high magnetic fields, i.e., magnetoresistance and Hall effect. Development of magnetic refrigerant materials based on giant magnetocaloric Mn compounds is also in progress.
Research
Research Interests
  • Transport Properties associated with exotic phase transitions in high magnetic fields
    keyword : magnetoresistance, Hall effect
    2013.04.
  • Search for exotic new superconductor
    keyword : superconductivity
    2008.10.
  • Development of magnetocaloric materials
    keyword : magnetocaloric effect, magnetic refrigeration, first-order magnetic transition
    2003.04.
  • Giant magnetocaloric effect of itinerant electron ferromagnets
    keyword : itinerant electron metamagnetism, magnetocaloric effect, pressure effect, structural transition
    1998.04.
  • Valence transition and Valence order of rare-earth compounds
    keyword : 4f electron system, valence fluctuation, valence transition, valence ordering, Yb, Eu
    1996.04.
Academic Activities
Papers
1. Akihiro Mitsuda, Shigeki Manabe, Masafumi Umeda, Hirofumi Wada, Kazuyuki Matsubayashi, Yoshiya Uwatoko, Masaichiro Mizumaki, Naomi Kawamura, Kiyofumi Nitta, Naohisa Hirao, Yasuo Ohishi, Naoki Ishimatsu, Emergence of a new valence-ordered structure and collapse of the magnetic order under high pressure in EuPtP, Journal of Physics Condensed Matter, 10.1088/1361-648X/aaaca3, 30, 10, 2018.02.
2. Hirofumi Wada, Yusuke Goki, Akihiro Mitsuda, Transport properties of EuNi2Ge2 under high pressure, Journal of the Physical Society of Japan, 10.7566/JPSJ.87.034707, 87, 3, 2018.01.
3. Katsuya Ichiki, Kojiro Mimura, Hiroaki Anzai, Takayuki Uozumi, Hitoshi Sato, Yuki Utsumi, Shigenori Ueda, Akihiro Mitsuda, Hirofumi Wada, Yukihiro Taguchi, Kenya Shimada, Hirofumi Namatame, Masaki Taniguchi, Hard x-ray photoemission study of the temperature-induced valence transition system EuNi2(Si1-xGex)2, Physical Review B, 10.1103/PhysRevB.96.045106, 96, 4, 2017.07.
4. Hirofumi Wada, Yoshiro Maekawa, Daichi Kawasaki, High-field transport properties of itinerant electron metamagnetic Co(S1-xSex)2, Journal of Science: Advanced Materials and Devices, 10.1016/j.jsamd.2016.06.001, 1, 2, 179-184, 2016.06, The Co(S1-xSex)2 compounds are known to exhibit itinerant electron metamagnetism (IEM). We present field dependence of electrical resistivity and Hall effect of the compounds with 0 ≤ x < 0.15. It was found that the magnetoresistance shows a positive jump associated with the IEM. This jump is nearly independent of temperature. We also observed a jump in the field dependence of Hall resistivity, which is attributable to the anomalous Hall effect due to the onset of ferromagnetism. Our analyses revealed that the ordinary Hall coefficient decreases considerably by the IEM. These results are discussed in terms of the proposed electronic structure of CoS2, in which a highly spin polarized state is achieved..
5. Hirofumi Wada, T. Takahara, K. Katagiri, T. Ohnishi, K. Soejima, K. Yamashita, Recent progress of magnetocaloric effect and magnetic refrigerant materials of Mn compounds (invited), Journal of Applied Physics, 10.1063/1.4914120, 117, 17, 2015.05, Magnetocaloric and related properties of Ru and Ni substituted (MnFe)2(PSi) are presented. It is found that Ru and Ni are effective doping elements to reduce the thermal hysteresis of (MnFe)2(PSi). The origin of the thermal hysteresis is discussed on the basis of a thermodynamic model. It is shown that the elastic energy is responsible for the thermal hysteresis. We also show recent developments of the production process of Mn compounds in an industrial scale..
6. T. Koyama, T. Maruyama, K. Ueda, T. Mito, Akihiro Mitsuda, M. Umeda, M. Sugishima, Hirofumi Wada, Zero-field NMR and NQR studies of magnetically ordered state in charge-ordered EuPtP, Physical Review B - Condensed Matter and Materials Physics, 10.1103/PhysRevB.91.094419, 91, 9, 2015.03, EuPtP undergoes two valence transitions and has two kinds of valence states of Eu ions at low temperatures. In the charge-ordered state, this compound shows an antiferromagnetic order ascribed to magnetic divalent Eu ions. We investigated the antiferromagnetically ordered state of EuPtP by nuclear magnetic resonance (NMR) measurement and nuclear quadrupole resonance (NQR) measurement in a zero external magnetic field. The observed Eu153 NMR signals of a magnetic divalent state and Eu151,153 NQR signals of a nonmagnetic trivalent state clearly demonstrate that the spins order in the hexagonal basal plane and the internal magnetic field is not canceled out, even at the Eu3+ layers which are in the middle of magnetic Eu2+ layers. In addition, the observation of 31P and Pt195 NMR spectra allowed us to discuss a possible magnetic structure. We also evaluated the nuclear quadrupole frequencies for both Eu2+ and Eu3+ ion states..
7. T. Mito, K. Nishitani, T. Koyama, H. Muta, T. Maruyama, G. Pristáš, K. Ueda, T. Kohara, Akihiro Mitsuda, M. Sugishima, Hirofumi Wada, NMR studies of ordered structures and valence states in the successive valence-transition system EuPtP, Physical Review B - Condensed Matter and Materials Physics, 10.1103/PhysRevB.90.195106, 90, 19, 2014.11, We have studied EuPtP, which undergoes two successive valence transitions at TA∼240 K and TB∼200 K by P31-nuclear magnetic resonance (NMR) measurements. From the analysis of NMR spectra, we obtained plausible ordered structures and Eu valence states in three phases divided by TA and TB. These ordered structures well explain observed inequivalent P sites and the intensity ratio of the NMR spectra arising from these P sites. The results are also in good accordance with mean Eu valence measured by the x-ray absorption spectroscopy. We also discuss Eu 4f states and the origin of the transitions from the measurements of nuclear spin lattice relaxation rate and hyperfine coupling constant..
8. K. Katagiri, K. Nakamura, Hirofumi Wada, Magnetocaloric properties and magnetic refrigerant capacity of MnFeP1-xSix, JOURNAL OF ALLOYS AND COMPOUNDS, 10.1016/j.jallcom.2012.11.127, 553, 286-290, 2013.03.
9. M. Sugishima, K. Yamada, A. Mitsuda and H. Wada, Effects of magnetic field and pressure on the intermediate valence state of YbPd, J. Phys: Condens. Matter, 22, 37, 375601, 2011.08.
10. A. Mitsuda, T. Okuma, K. Sato, K. Suga, Y. Narumi, K. Kindo and H. Wada, Pressure and magnetic field dependence of valence and magnetic transitions in EuPtP, J. Phys: Condens. Matter , 22 , 22, 226003, 2010.05.
11. Y. H. Matsuda, Z. W. Ouyang, H. Nojiri, T. Inami, K. Ohwada, M. Suzuki, N. Kawamura, A. Mitsuda and H. Wada , X-ray Magnetic Circular Dichroism of a Valence Fluctuating State in Eu at High
Magnetic Fields
, Phys. Rev. Lett., vol. 103 (2009) 046402-1-4., 2009.07.
12. A. Mitsuda, K. Yamada, M. Sugishima and H. Wada, Pressure effect on valence fluctuation and magnetic ordering in YbPd, Physica B, vol. 404 (2009) 3002-3004, 2009.07.
13. H. Wada, S. Matsuo, and A. Mitsuda, Pressure dependence of magnetic entropy change and magnetic transition in MnAs1-xSbx, Phys. Rev. B, vol. 79 (2009) 092407-1-4, 2009.03.
14. H. Wada, C. Funaba, T. Asano, M. Ilyn and A. M. Tishin, Recent progress of magnetocaloric effect of MnAs1-xSbx, Proc. Int. Conf. IIR on Magnetic Refrigeration at Room Temperature, Montreux, Ed. P. Egolf, (IIR-IIF, Paris, 2005), 37-46, p37-p46., 2005.01.
15. T. Morikawa and H. Wada, Effect of deviation from stoichiometry on magnetic and magnetocaloric properties in MnAs1-xSbx, J. Magn. Magn. Mater., vol. 272-276, Supplement 1, E583-584., 2004.08.
16. T. Tohei, H. Wada and T. Kanomata, Negative magnetocaloric effect at the antiferromagnetic to ferromagnetic transition of Mn3GaC, J. Appl. Phys., vol. 94, 1800-1802., 2003.08.
17. H. Wada, T. Morikawa, K. Taniguchi, T. Shibata, Y. Yamada and Y. Akishige, Giant magnetocaloric effect of MnAs1-xSbx in the vicinity of first-order
magnetic transition, Physica B, vol. 328, 114-116., 2003.04.
18. H. Wada, H. Yoshioka, T. Goto, K. Koyama and K. Watanabe, Novel field-induced magnetic transitions of GdMn2Ge2, J. Phys. Soc. Japan, vol.72, No.12, 3197-3203., 2003.12.
19. H. Wada, K. Taniguchi and Y. Tanabe, Extremely large magnetic entropy change of MnAs1-xSbx near room temperature, Mater. Trans., vol.43, No.1, 73-77., 2002.01.
20. H. Wada and Y. Tanabe, Giant magnetocaloric effect of MnAs1-xSbx, Appl. Phys. Lett., vol. 79, No.20, 3302-3304., 2001.11.
21. H. Wada, H. Gomi, A. Mitsuda and M. Shiga, Specific heat anomaly due to valence transition in Eu(Pd1-xPtx)2Si2, Solid State Commun., vol.117, 703-707., 2001.02.
Presentations
1. H. Wada, T. Takahara, K. Katagiri, K. Sadamatsu, T. Ohnishi, K. Soejima, K. Yamashita, Recent progress of magnetocaloric effect and magnetic refrigerant materials of Mn- and Fe-based compounds, Magnetism and Magnetic Materials Conference, 2014.11.
2. 和田 裕文, Magnetocaloric Effect and Magnetoresistance due to Itinerant Electron Metamagnetic transition in Co(S1-xSex)2, 2013.11.
3. Hirofumi Wada, Mn-Based compounds for magnetocaloric applications at room temperature, 5th IIR/IIF International Conference on Magnetic Refrigeration at Room Temperature, THERMAG V, 2012.09.