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Oral presentation

Magnetic excitations in spin gap system

Kakurai, Kazuhisa; Matsuda, Masaaki; Hase, Masashi*; Ozawa, Kiyoshi*; Kitazawa, Hideaki*; Tsujii, Naoto*; Doenni, A.*; Hu, X.*; Kuroe, Haruhiko*

no journal, , 

We report powder sample inelastic neutron scattering experiments on spin gap systems. Recently the magnetization plateau phenomenon in quantum spin systems are drawing attention of both theoretical and experimental physicists. Although the relevant exchange energies can be estimated from the magnetic susceptibility measurements assuming some theoretical models, we can only speculate the exchange interaction scheme causing the singlet ground state based on the structural and bonding information. We shall present examples of powder sample inelastic neutron scattering studies on the antiferromagnetic alternating chain system $$beta$$-AgCuPO$$_{4}$$ and trimer chain compound Cu$$_{3}$$(P$$_{2}$$O$$_{6}$$OD)$$_{2}$$ using triple axis spectrometer at the steady state neutron source and stress that this kind of research on novel quantum systems could be very effectively performed using the low-energy chopper type spectrometer being built for the J-PARC spallation neutron source.

Oral presentation

Neutron diffraction study of rare-earth compound Ho$$_5$$Pd$$_2$$ with a large magnetocaloric effect

Kitazawa, Hideaki*; Kawamura, Yukihiko*; Terada, Noriki*; Mamiya, Hiroaki*; Suzuki, Hiroyuki*; Doenni, A.*; Kaneko, Koji; Metoki, Naoto; Igawa, Naoki

no journal, , 

We have performed neutron powder diffraction experiments at JRR-3 using polycrystalline Ho$$_5$$Pd$$_2$$. The magnetic peaks with a propagation vector k = (0.18, 0.18, 0.18) are gradually developing below about 100 K. The peak width is significantly broader than an experimental resolution even temperature is 5 K. These results indicate that Ho$$_5$$Pd$$_2$$ is a short-range ordered antiferromagnet with a long wave length.

Oral presentation

Neutron scattering study toward to development of energy-efficient environment-friendly refrigeration technology

Kitazawa, Hideaki*; Kawamura, Yukihiko*; Mamiya, Hiroaki*; Terada, Noriki*; Suzuki, Hiroyuki*; Tsujii, Naohito*; Doenni, A.*; Kaneko, Koji; Metoki, Naoto; Igawa, Naoki; et al.

no journal, , 

In this paper, we will demonstrate some application of neutron scattering for magnetic refrigerant materials Ho$$_5$$Pd$$_2$$ and dilute spinel ferrites. In order to determine the magnetic structure, we have performed neutron powder diffraction experiments at JRR-3. The magnetic peaks with a propagation vector k = (0.18, 0.18, 0.18) are gradually developing. The peak width is significantly broader even 5 K, indicating a short-range order with a long wave length.

Oral presentation

Giant magnetocaloric effect and short-range ordering of magnetic refrigerant materials R$$_5$$Pd$$_2$$(R=Tb, Ho)

Kitazawa, Hideaki*; Kawamura, Yukihiko*; Keller, L.*; Toyoizumi, Saori*; Terada, Noriki*; Suzuki, Hiroyuki*; Mamiya, Hiroaki*; Doenni, A.*; Lee, S.*; Metoki, Naoto; et al.

no journal, , 

Neutron Scattering study has been carried out in order to reveal the magnetic structure of the antiferromagnet Ho$$_5$$Pd$$_2$$, which shows giant magnetocaloric effect. We observed short rage magnetic order at k=0.18, 0.18, 0.18 above the antiferromagnetic transition temperature $$T$$$$_N$$. Tb$$_5$$Pd$$_2$$ also showed magnetic short range correlation above the temperature higher than 2$$times$$$$T$$$$_N$$.

Oral presentation

Short-range ordering of magnetic refrigerant materials $$R_5$$Pd$$_2$$ (R = Ho, Tb) by neutron diffraction

Kitazawa, Hideaki*; Kawamura, Yukihiko*; Keller, L.*; Terada, Noriki*; Suzuki, Hiroyuki*; Mamiya, Hiroaki*; Doenni, A.*; Lee, S.*; Metoki, Naoto; Kaneko, Koji; et al.

no journal, , 

Antiferromagnetic Ho$$_5$$Pd$$_2$$($$T_{rm N} = 28$$K) with cubic structure accompanies very large magneto-calorimetric eefect (MCE) at 34K. We showed that this compound remains short range order with incommensurate modulation $$k=$$[0.18,0.18,0.18] developing at low temperatures. The short range correlation increases below 70K in Tb$$_5$$Pd$$_2$$($$T_g = 70$$K).

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