@phdthesis{oai:muroran-it.repo.nii.ac.jp:00009956,
 author = {GUO, Qing and 国, 慶},
 month = {2019-06-25, 2019-06-25},
 note = {application/pdf, Since binary rare earth chalcogenides exhibit diverse and interesting physical properties, they have been vigorously studied about their composition and crystal structure. For example, the rare earth sulfides ?-R2S3 (R = Tb, Dy) with tetragonal crystal structure exhibit peculiar successive antiferromagnetic transitions. The rare earth tellurides RTe3 (R = Gd, Tb, Dy) with layered structure exhibit charge density wave (CDW) transition and superconducting transition under pressure. In the writer research on a series of rare earth chalcogenides, the magnetocaloric effect (MCE) of ?-R2S3 (R = Tb, Dy) and the physical properties of GdTe3 in high magnetic field and low temperature region were investigated in advance. In addition to such attractive physical properties of rare earth compounds, many characteristic physical properties have also been reported for rare earth compounds including transition metals. In these transition-metal rare earth compounds, there still exist no-studied areas and it is a possible that unknown substances may be hidden, which exhibit novel physical properties leading to materials useful for the next generation society. So in this study, we aimed to search for new rare earth chalcogenides including transition metal. As a result, I discovered new transition-metal rare earth chalcogenides R10NiTe9 (R = Gd, Tb) and investigated their magnetic and electrical properties in detail. Single crystals of R10NiTe9 were grown by heat treatment of a mixture of R, R3Ni and R2Te3. SEM-EDX analysis confirmed that the ratio of R, Ni and Te was about 10: 1: 9. XRD analysis revealed that the obtained single crystal was NaCl-type structure with space group Fm-3m at room temperature. It was concluded that in this structure Ni was randomly substituted Te in a ratio of 1 per 10. In terms of magnetism, the following points have been clarified. (A) In the case of Gd10NiTe9, (1) it exhibits a ferromagnetic transition at 168 K. It implies that I succeeded in emerging ferromagnetism at high temperature by slightly incorporating Ni into GdTe having an antiferromagnetism at a lower temperature. (2) In the magnetization process at low temperature, it has been found that there is a region where the magnetization decreases with increasing the magnetic field. It was also concluded to be cooperative phenomenon between the rare earth element Gd and the transition metal element Ni. (B) For Tb10NiTe9, (1) Two peaks suggesting successive magnetic transitions were found below 120 K in the temperature dependence of magnetization. (2) A remarkable FC / ZFC effect was found below a temperature at which the high temperature side magnetic transition occurs. As for electrical conductivity, the followings were clarified. In both compounds Gd10NiTe9 and Tb10NiTe9, (1) electrical resistivity is about 104 times greater than conventional metal at room temperature. (2) Temperature dependence of electrical resistivity is extremely weak, and the value of electric resistivity hardly changes down to about 50 K. (3) Temperature dependence of electrical resistivity shows a sharp rise below about 50 K. As mentioned above, single crystals of Gd10NiTe9 and Tb10NiTe9 were successfully grown, as new rare earth chalcogenides including Ni, and exhibited novel physical properties on magnetism and electrical conductivity. This result seems to open up a new way to study deepened physical properties of the present compounds, research on physical properties in new compound group R10NiTe9 and develop new materials., 二元系希土類カルコゲナイドは多様で興味深い物性を示すので、その組成・結晶構造とともに精力的に研究されてきた。例えば、直方晶系の結晶構造を有する希土類硫化物α-R2S3（R = Tb、Dy）は、特異な逐次的反強磁性転移を示す。層状構造を有する希土類テルル化物RTe3（R = Gd、Tb、Dy）は、電荷密度波（CDW）転移や圧力下での超伝導転移を示す。筆者の一連の希土類カルコゲナイドに関する研究の中で、α-R2S3（R = Tb、Dy）の磁気熱量効果（MCE）と高磁場・低温域におけるGdTe3の物性を先行的に調べた。希土類化合物のこの様な魅力的な物性に加えて、遷移金属を含有した化合物についても多くの特徴的物性が報告されている。この遷移金属含有希土類化合物には、未開の領域が広く存在しており、次世代社会に有益な材料に繋がる新奇物性を発現する未知物質が潜んでいる可能性があるため、本研究では、遷移金属を含有した新しい希土類カルコゲナイドを探索することを目的とした。その結果、筆者は新しい遷移金属含有希土類カルコゲナイドR10NiTe9（R = Gd、Tb）を発見し、これらの磁性と伝導について詳細に調べた。R10NiTe9の単結晶は、R、R3NiおよびR2Te3の混合物の熱処理によって育成された。SEM-EDX分析により、R、NiおよびTeの比が約10：1：9であることが確認された。XRD分析より、得られた単結晶が室温で空間群Fm-3mを有するNaCl型構造のR10NiTe9であることを明らかにした。この構造中でNiはTe10個につき1個の割合で置換する形でランダムに入っていると結論した。磁性の面では次のことを明らかにした。（A）Gd10NiTe9に関して、（1）168 Kで強磁性転移を示す。この意義深い点は、より低温で反強磁性転移を示すGdTeにわずかにNiを含有させたことにより、高温での強磁性を発現させることに成功したことである。さらに、（2）低温における磁化過程において、磁場の増加に対して磁化が減少する領域が存在するという希有な現象を見出した。これに関しても希土類元素Gdと遷移金属元素Niとの協力現象であると結論した。（B）Tb10NiTe9に関しては、（1）120 K以下で二段の逐次磁気転移を示唆する二つのピークを磁化の温度依存性に見出した。また（2）高温側転移点より低温で顕著なFC/ZFC効果も見出した。導電性に関しては、次のことを明らかにした。Gd10NiTe9, Tb10NiTe9両化合物において、（1）電気抵抗率は室温で通常の金属より10 4倍程度以上大きい。（2）その温度依存性は極めて弱く、電気抵抗率の値は50 K 程度までほとんど変化しない。（3）50Kより低温で電気抵抗率が急激な上昇を示す。以上のように新規Ni含有希土類カルコゲナイドGd10NiTe9, Tb10NiTe9の単結晶育成に成功し、磁性と伝導における新奇物性を見出した。この結果は同化合物におけるさらなる深化した物性研究、また新規の化合物群R10NiTe9における物性研究ならびに新材料開発への新たな途を開くと考えられる。},
 school = {室蘭工業大学, Muroran Institute of Technology},
 title = {Study on single crystal growth and physical properties of new rare-earth chalcogenides including Ni},
 year = {}
}