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硫化ビスマス超伝導体LaO1-xFxBi1-ySbyS2における不純物効果と超伝導に関する研究
Get PDF室蘭工業大学Muroran Institute of Technology博士（工学）application/pdf近年、様々な新しい層状超伝導体（SC）が発見され、注目されている。 その一つに、2012年に発見された超伝導転移温度Tc = 8.6 Kの層状化合物Bi4O4S3がある。この系は様々なバリエーションがあり、高圧下では、10KのTcを持つ（Eu、Sr）3F4Bi2S4が合成された。また、酸素のフッ素置換により、Tc = 2–10 KのLnO1-xFxBiS2（Ln = La、Ce、Pr、Nd、Yb）化合物も見つかった。さらに、SをSeに置き換えたLaO1-xFxBiCh2（Ch = S、Se）も超伝導を示すことが報告された。ドープされたSeは、LaO1-xFxBiCh2（Ch = S、Se）の面内Sサイトを優先的に占有し、最大Tc = 4 Kとなる。これらの化合物は、伝導を担うBiS2層とBiS2層に電子を供給するブロッキング層（LaO / F）が交互に積層した特徴的な構造を有する。この層状結晶構造は、興味深いことに、高温（高Tc）銅酸化物およびFeベースの超伝導体と類似している。BiS2超伝導体の超伝導のメカニズムは未だ不明のままであり、銅酸化物やFe系超伝導体とは異なるメカニズムと考えられている。超伝導発現メカニズムの起源を反映するものとして、超伝導ギャップの対称性がある。LaおよびNdベースのBiS2超伝導体における磁気侵入長と熱伝導率の測定からs波超伝導ギャップが報告されている。一方、磁場侵入長測定(TF-μSR)からSCギャップは異方的なs波と、s++波で実験結果を良く表すことができると報告されている。そして角度分解光電子分光（ARPES）実験からは、超伝導ギャップの大きな異方性が報告され、超伝導ギャップにノードが存在する可能性が示唆されている。また、トンネル分光実験からは、超伝導ギャップの対称性が従来とは異なるものであることが報告されている。このように、BiS2系超伝導体の超伝導ギャップの対称性についてはまだ議論がつづいており、その解明はこの系の超伝導発現メカニズムを解明する上で急務となっている。BiS2系超伝導体の中でも、特にLaO1-xFxBiS2化合物は系統的にキャリア数を変化させることができることから、これまで集中的に研究されてきた。本研究では、LaO1-xFxBiS2超伝導体の超伝導ギャップ対称性と超伝導性を明らかにする目的で、XRD、比熱、電気抵抗率、磁化率測定を通じて、層状超伝導体LaO1-xFxBi1-ySbyS2に対するSb置換の影響を調べた。LaO1-xFxBiS2（x = 0.5、0.4）およびLaO0.5F0.5Bi1-ySbyS2（y = 0–0.20）の単結晶試料は、大気圧下でフラックス法により作製された。得られたLaO1-xFxBiS2（x = 0.5、0.4）単結晶はどれもバルクの超伝導性を示し、そのTcはx = 0.5で約2.5 K、x = 0.4ではわずかに抑制され、約2.4 Kであった。LaO1-xFxBiS2（x = 0.5）の電子比熱Ceは、異方的な単一ギャップまたは2ギャップのs波超伝導によってよく理解できるものであった。x = 0.4の場合、特に2ギャップ効果が顕著であった。また、非磁性不純物としてSbを添加したLaO0.5F0.5Bi1-ySbyS2では、T << TcでのCe/Tが少量のSb置換によってほとんど回復しなかった。この結果はLaO1-xFxBiS2の超伝導がs-波であることを意味する。さらに、比熱の温度依存性、電気抵抗率、磁化率測定から決めたTcはSbドーピングによって抑制されるが、これはSb不純物による対破壊効果というよりは、キャリアの弱局在によって電子相関が強まったためと考えられる。以上の結果より、LaO1-xFxBiS2の超伝導はフルギャップのs波超伝導であると結論した。Recently, significant discoveries have been made in the use of layered materials in novel superconducting (SC) materials. In 2012, superconductivity was discovered in the layered compound Bi4O4S3 with SC transition temperature Tc = 8.6 K. Later, (Eu, Sr)3F4Bi2S4 was synthesized under high pressure with Tc = 10 K. Superconductivity was also discovered in LnO1-xFxBiS2 (Ln = La, Ce, Pr, Nd, Yb) compounds with Tc = 2–10 K through fluorine substitution for oxygen. Further, S can be substituted by Se, and the doped Se preferentially occupies the in-plane S site in LaO1-xFxBiCh2 (Ch = S, Se) with maximum Tc = 4 K. In particular, the superconductivity of LaO1-xFxBiS2 compounds has been studied intensively. These compounds have a characteristic structure with an alternate stacking of SC BiS2 layers and blocking layers (LaO/F) that supply electrons to the BiS2 layers. The layered crystal structure is analogous to those of high-temperature (high-Tc) cuprate and Fe-based superconductors. However, the mechanism underlying the superconductivity of BiS2 superconductors, which still remains unclear, is considered to be different from those of cuprate and Fe-based superconductors. The symmetry of the SC gap is well known to reflect the origin of the SC mechanism. Magnetic penetration depth measurements and thermal conductivity measurements for La- and Nd-based BiS2 superconductors have shown a full gap with an s-wave. However, transverse-field muon spin relaxation (TF-μSR) measurements have proposed that the SC gap is well described by two-gap s + s-wave model and anisotropic s-wave model. Soon after that, angle-resolved photoemission spectroscopy (ARPES) measurements indicated a large SC gap anisotropy and suggested the existence of accidental nodes in nodal s-wave symmetry. Recently, point contact spectroscopy measurements have suggested that the gap symmetry is an unconventional pairing symmetry. Thus, the SC gap symmetry of BiS2-based superconductors remains controversial. In this work, we investigated the SC gap symmetry and bulk nature of superconductivity in LaO1-xFxBiS2 superconductors, and the effect of Sb substitution on the layered superconductor LaO1-xFxBi1-ySbyS2 through XRD, specific heat, electrical resistivity, and magnetic susceptibility measurements. LaO1-xFxBiS2 (x = 0.5, 0.4) and LaO0.5F0.5Bi1-ySbyS2 (y = 0–0.20) were synthesized using the flux method under ambient pressure. LaO1-xFxBiS2 (x = 0.5, 0.4) show bulk nature of superconductivity, although Tc is slightly suppressed, and its transition is broad for x = 0.4. The electronic specific heat Ce of LaO1-xFxBiS2 (x = 0.5) below ~ Tc can be explained by s-wave superconductivity with either an anisotropic single gap or two gaps. The two-gap effect is more dominant for x = 0.4. The Ce/T at T<<Tc in LaO0.5F0.5Bi1-ySbyS2 below y = 0.06 is hardly recovered by Sb substitution, indicating that the superconductivity is robust against the pair-breaking due to non-magnetic impurities, as expected in the fully gapped s-wave superconductivity. Tc is suppressed by the Sb-doping in both the specific heat and the electrical resistivity and magnetic susceptibility measurements. The slight decrease in Tc in Sb-doped samples can be ascribed to the enhancement of electron correlations due to the weak localization of carriers. Based on these experimental results, we conclude that LaO1-xFxBiS2 compound shows a fully gapped s-wave superconductivity.
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β-LiAlSiO4結晶の温度変化シミュレーション
Get PDFapplication/pdfAnisotropic low-thermal expansion of β-LiAlSiO4 crystal was reproduced by MD calculation applying a potential model of a spherically symmetric two-body interatomic interaction. From the correlation between the Si-O-Al angle and the Si-Al distance in the c-axis direction, the expansion of a-axis and the contract of c-axis brings the split of Si-O-Al angle distribution. At the same time, the stable position of Li+ ion sites also changed. This suggests the cation position also important in the mechanism of low-thermal expansion observed in silicate materials.journal articl
The elevated temperature and gas component within an operating semi-aerobic landfill
Get PDFapplication/pdfThe semi-aerobic landfill concept, which is based on passive aeration, is the compulsory standard for planning new landfill projects in Japan. The semi-aerobic landfill concept is also applied in several other countries because of its low construction and operating costs. The landfill gas (LFG) component and the LFG temperature are the main indicators of the aerobization of semi-aerobic landfills. Analysis of LFG, its concentration, and its temperature can be easily carried out on-site to evaluate the passive aeration of an operating semi-aerobic landfill. Therefore, this study observed LFG temperatures and LFG components to assess the partial aerobization within an operating semi-aerobic landfill. The observational data revealed that the methane (CH4) gas concentration of most of the main LFG venting pipes (VPs) was below 15%. The aerobic condition happened effectively surrounding the main LFGVP M2 because over the observation period, the ratio of CH4 to CO2 was less than 1.0. The highest gas temperature was above 60°C within the main LFGVP M2, and there was a trend of high temperatures above 40°C for more than 5 years before the temperature declined to 20°C in the most recent observation. The high LFG temperatures were recorded in the winter months due to the buoyancy effect. High temperature and the CH4/CO2 ratio less than 1.0 potentially representing good indicators showed that aerobic decomposition is becoming dominant. The study showed clearly that the aerobic biodegradation performance in this semi-aerobic landfill is extremely good.journal articl
Photomechanical Behaviors of Azobenzene-based Amorphous Molecular Materials: Photoinduced Structural Changes of Amorphous Films of 4-[Bis(9,9-dimethylfluoren-2-yl)amino]azobenzene Analogues Fabricated on the Surface of Agar Gel
Get PDFapplication/pdfPhotomechanical behaviors of the films of 4-[bis(9,9-dimethylfluoren-2-yl)amino]-4'-cyanoazobenzene (CN-BF1AB) and 4-[bis(9,9-dimethylfluoren-2-yl)amino]-4'-nitroazobenzene (NO2-BF1AB) fabricated on the surface of agar gel have been investigated. Two-stage process including striped pattern formation and the subsequent band-like structure formation was observed upon irradiation with a linearly polarized laser beam with 488 nm, being similar to the result for the film of the parent compound, 4-[bis(9,9-dimethylfluoren-2-yl)amino]azobenzene (BF1AB). The rate of such structural change for CN-BF1AB was almost similar to or somewhat slower than that for BF1AB film. On the other hand, the rate for NO2-BF1AB was considerably slower than those for BF1AB and CN-BF1AB. The results suggested that the photochromic reactivity of the molecule in the amorphous film plays a role for the present photomechanical behaviors.journal articl
A Study on the Management of a Model Area Considering Childcare Support and Mutual Assistance to Overcome Population Decline in Funahashi Village, Toyama Prefecture
Get PDFapplication/pdfIn recent years, the community development by the childcare support and mutual assistance that contributes to regional revitalization policy is expected to overcome a declining population. Under such a background, we clarified the change of consciousness of users of a model area considering childcare support and mutual assistance in Funahashi Village, Toyama Prefecture. A questionnaire survey was distributed to the service users of the model area to identify (1) factors affecting the rating of the service (satisfaction with each service item), (2)overall rating of the service (overall satisfaction), and (3) changes in user’s consciousness regarding "participation in childcare services", "mutual assistance", "emigration and settlement." After collecting questionnaire responses, covariance structure analysis was conducted to verify the relationship among valuables of these 3 questions. We found that the change of user’s consciousness (3) was directly affected by satisfaction with “each service item” (1) and “overall satisfaction” (2). Considering these findings, we proposed appropriate directions for the future development of the community development by childcare support and mutual assistance and the direction of new business style reform in the landscaping industry.journal articl
The Meanings of <Passive> Shared by the Passive Voice and the Causative Voice in Mongolian
Get PDFapplication/pdfThe purpose of this article is to elucidate the meanings of passive shared by the passive voice and the causative voice in the Mongolian language. Fundamentally, the passive and the causative construct different sentences both morpho-syntactically and semantico-functionally. The passive sentences focus the patient, while the causative sentences highlight the relationship between the causer and the agent. However, some passive and causative sentences share the passive meanings with each other. By considering the morphological-syntactic and semantic-functional characteristics of the passive and the causative separately, we will find out what factors work to generate the common meaning of and what differences the two voices have in them.journal articl
Non-contact imaging of peripheral hemodynamics during cognitive and psychological stressors
Get PDFapplication/pdfPeripheral hemodynamics, measured via the blood volume pulse and vasomotion, provide a valuable way of monitoring physiological state. Camera imaging-based systems can be used to measure these peripheral signals without contact with the body, at distances of multiple meters. While researchers have paid attention to non-contact imaging photoplethysmography, the study of peripheral hemodynamics and the effect of autonomic nervous system activity on these signals has received less attention. Using a method, based on a tissue-like model of the skin, we extract melanin Cm and hemoglobin CHbO concentrations from videos of the hand and face and show that significant decreases in peripheral pulse signal power (by 36% +/- 29%) and vasomotion signal power (by 50% +/- 26%) occur during periods of cognitive and psychological stress. Via three experiments we show that similar results are achieved across different stimuli and regions of skin (face and hand). While changes in peripheral pulse and vasomotion power were significant the changes in pulse rate variability were less consistent across subjects and tasks.journal articl
“Research Project Report: Studies on Better Motivation in Foreign Language Learning from Various Angles -Part3-” by Linguistic Science and International Relations Research Unit, Muroran Institute of Technology
Get PDF本稿は、室蘭工業大学ひと文化系領域言語科学・国際交流ユニットが3 か年計画で取り組んでいる言語文化と語学教育に関する研究と教育の成果報告である。当該ユニットに所属する教員が3 つのグループを組織し、言語学、言語教育、異文化理解の観点からいかにして日本語教育を含む外国語教育の改善に取り組んできたのか、その成果を広く公表することを目的とする。今回は、成果報告の第3 弾である。research repor
海岸道路の防波施設の波浪による変状特性とその対策に関する実証的研究
Get PDF室蘭工業大学Muroran Institute of Technology博士（工学）application/pdf四方を海に囲まれた北海道では海岸線に沿って国道が整備され，1980年代以降は，交通量の増大に対応して，海側への車線拡幅やバイパス化が進められた.その際，多くの区間で防波施設が新設され，高波時の安全確保に大きな役割を果たした.しかしながら近年，防波施設の洗堀や摩耗といった経年的な変状が顕在化してきた.さらに急勾配海底地形に建設された防波施設では，消波ブロックの沈下や散乱が急速に進行し，背後の道路関連施設に大きな被害をもたらした.こうした防波施設の変状の発生メカニズムを解明し，その対策を講じるための知見を取りまとめ，設計者に周知させることが急務となっている．本研究ではまず，北海道の各海域における海岸道路を対象として，防波施設における洗掘および摩耗の発生状況と，急勾配海底地形における海岸道路の防波施設の被災状況について調査し，現地において対策工を設計する上での課題を整理した．防波施設の洗掘については，砂浜海岸において高波浪の継続によって施設前面の洗堀が急速に進行し，道路盛土の崩壊やそれに伴う道路施設の倒壊に至ることを示した．こうした洗堀に伴う重大災害に共通する要因は前浜の減少であり，定期的なモニタリングによる現状把握と，適切な消波工の設置が必要であることを示した．防波施設の摩耗については，代表的な直立消波構造形式であるスリット式護岸と直積ブロック式護岸を対象として水理模型実験を行い，波浪に連行された粗石の衝突の発生メカニズムを明らかにした.その上で既往の摩耗量算定式と組み合わせることにより，各部材の摩耗量の予測方法を提案した．さらにUAV（無人航空機）を活用した摩耗調査方法を提案するとともに，新しいタイプの摩耗対策である超高強度繊維補強材料の耐摩耗性の評価を行い，国道336号広尾海岸における施工事例に基づいて，その実用性を示した．急勾配海底地形条件に対しては，代表的なカルデラ湖である支笏湖の湖岸道路と，積丹半島の急崖区間における道路関連施設の2例について，現地における被災状況を分析した．さらに数値波動解析と水理模型実験を用いた系統的な検討を行い,急斜面に続くリーフの幅が，消波ブロックの耐波安定性に及ぼす影響を明らかにした.これらの結果に基づいてハドソン式を用いた従来の算定式の補正法を提案した.また，支笏湖のようにリーフ幅が狭く大質量の消波ブロックの設置が困難な条件への対処法として，根固ブロックを用いた補強工の設計法を提案した．Numerous roads running along the coast of Hokkaido have been widened seaward since the 1980s or been complemented with bypasses to accommodate increased traffic volumes, and seawalls constructed along many of these new sections have played a significant role in securing safety against high waves. In recent years, however, damage to these seawalls caused by abrasion and scouring have become increasingly apparent. For seawalls built on steep ocean beds in particular, subsidence and scattering of wave-dissipating concrete blocks have been progressing rapidly, causing significant damage to road-related facilities behind them. Against this background, there is an urgent need to elucidate the mechanism of seawall damages and to inform practical countermeasures for seawall designers. Targeting several coastal roads, this study first investigated the current state of abrasion and scouring in seawalls as well as damage to seawall facilities on steep ocean beds, and identified challenges in designing related countermeasures. The outcomes showed that scouring rapidly progresses at the front of seawall facilities in sandy coastal areas due to constant exposure to high waves, resulting in the collapse of highway embankments and road-related facilities. A factor common to such scouring was a reduced foreshore area, and it was found necessary to clarify foreshore conditions via regular monitoring and install appropriate wave-dissipating structures. To help clarify the characteristics of such abrasion, hydraulic model experiments were conducted on two typical vertical wave-dissipating structure types, such as slit-type seawall and block masonry seawall. Combining the findings with an existing abrasion amount calculation formula, a method for predicting abrasion on different components was proposed. A technique for surveying abrasion using an unmanned aerial vehicle (UAV) was also suggested, and the abrasion resistance of an ultra-high-strength fiber-reinforced material was evaluated. The practicality of this material was verified based on its use in construction work on road facilities at Hiro Coast. In relation to steep ocean bed conditions, on-site damage analysis was conducted for a coastal road at Lake Shikotsu and a clifftop road on the Shakotan Peninsula. Systematic investigations using numerical wave analysis and hydraulic model experiments were also conducted to elucidate how the width of reefs under steep slopes influences the anti-wave stability of wave-dissipating blocks. Based on the results, correction of conventional calculation based on the Hudson Formula was proposed. As a countermeasure for conditions such as those observed at Lake Shikotsu, design for a reinforcement structure based on foot protection blocks was proposed.
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希土類酸化物RMnO3における元素置換効果と化学圧力効果
Get PDF室蘭工業大学Muroran Institute of Technology博士（工学）application/pdfABO3型ペロブスカイトRMnO3（R:希土類元素）は同時に複数の秩序状態を持つマルチフェロイック物質として広く研究されている。本論文では、直方晶GdMnO3（空間群Pnma）と六方晶TmMnO3(P63cm)について、元素置換効果と化学圧力効果について調べた。GdMnO3のX線回折測定結果は、TN以下でAタイプの反強磁性であることを示しているが、Mnスピンは完全には反平行でなく、わずかにチルトしていることが知られている。これはキャント磁性あるいは弱強磁性と呼ばれている。この系のMnをCoで置換したGdMn1-xCoxO3の結晶構造は、0≦x≦1で直方晶系である。x=0.3,0.5,0.7では、転移温度Tcにおいて磁場中冷却(FC)磁化MFCは、温度低下とともにMnとCoモーメントのキャントの結果として急激に増加する。特に、x=0.3のMFCは約40Kで最大値を示し、温度の低下とともに急激に減少し、20K以下では負の磁化を示した。他方、重希土類酸化物TmMnO3は、反強磁性転移温度TNが41K, 強誘電転移温度TCが86Kである。この構造を持つRMnO3の結晶構造は、高圧合成により直方晶に変化することが知られているが、Coで置換したTmMn1-xCoxO3においてもその構造はxに依存して六方晶から直方晶系へ変化し、0.5≦xでは、直方晶単相(Pnma)を得た。TmMn1-xCoxO3のMFCは、温度の減少とともに、約60Kで強磁性的に増加し、0.6≦x≦0.7でも負の磁化を示す。しかし、x=0.8のMFCはもはや温度低下とともに強磁性的な増加を示さない。これらの温度低下に伴うTcでの強磁性的な磁化の増大は、Co置換による混合原子価状態の結果として理解できる。また負の磁化、すなわちスピン反転は、MnとCoモーメントに対するGdあるいはTmスピンの反強磁性的カップリングによって説明できる。我々はまた、GdやTm を非磁性希土類元素La、Y、Luで置換したGd1-yRyMn1-xCoxO3とTm1-yRyMn1-xCoxO3の物性についても調べた。Gd3+、Tm3+、La3+、Y3+、Lu3+のイオン半径の違いから、我々は、TmまたはGdを非磁性希土類元素で置換することによる単位格子体積(V)の変化による圧力効果を期待できる。Tm1-y(Y,Lu)yMn0.5Co0.5O3の調査から、いくつかの顕著な構造の詳細が得られた。Tm1-yLuyMn0.5Co0.5O3とTm1-yYyMn0.5Co0.5O3のVは、それぞれyの増加とともに減少と増加した。直方晶歪みを特徴づけるパラメータ(a-c)/aは、Tmイオンを置換するために、Luドープでは連続的に増加し、Yドープでは減少する。直方晶Tm1-y(Y,Lu)yMn0.5Co0.5O3におけるTmのYまたはLuによる置換は、系統的な単位格子体積の変化を誘起する。これは化学圧力効果である。磁化測定から、我々はMFCと単位胞体積の増加が転移温度TCにおける増加に寄与すると結論する。直方晶Gd1-yRyMn0.7Co0.3O3(R=非磁性希土類元素) のy=0.1,0.3,0.5についても、化学圧力効果の研究を行った。Gd1-yRyMn1-xCoxO3におけるGdのLa,Y,Lu置換は、単位胞体積の系統的な変化を誘起する。我々の結果は、化合物の希土類元素の平均イオン半径の増加あるいは減少が、磁気転移温度TCに影響することを示す。非磁性元素による置換で生じたGdの割合の減少は、スピン反転効果を弱める。The ABO3 type perovskite RMnO3 (R: rare-earth element) has investigated extensively as the multiferroic materials which possess two or more types of orders simultaneously. In this thesis, we investigated the effect of element substitution and chemical pressure in orthorhombic GdMnO3 (space group Pnma) and hexagonal TmMnO3 (P63cm). The X-ray diffraction measurement results of GdMnO3 shows A-type antiferromagnetism is below TN, but it is known that Mn spins are not perfectly antiparallel, but exist with a slight tilt. This is called cant magnetism or weak ferromagnetism. The crystal structure of GdMn1-xCoxO3 is orthorhombic for 0≤x≤1.0. For x=0.3, 0.5, and 0.7, at the ordering temperature TC, the field-cooled (FC) magnetization MFC rapidly increase which results from cating of the Mn and Co moments with decreasing temperature. Especially, MFC for x= 0.3 showed maximum values at 40K, decreased rapidly with decreasing temperature and showed a negative magnetization blow 20K. On the other hand, the heavy rare earth oxide TmMnO3 is that an antiferromagnetic transition temperature TN is 41K, and ferroelectric transition temperature TC is 86K. It is known that the crystal structure of RMnO3 having this structure changes to the orthorhombic (Pnma) by performing high-pressure synthesis, but even in TmMn1-xCoxO3 with substitution by Co the structure changes from hexagonal to an orthorhombic, and we can obtain an orthorhombic single phase (Pnma) at 0.5≤x. MFC of TmMn1-xCoxO3 was increase in ferromagnetically at about 60K with decreasing temperature, and also showed negative magnetization in 0.6≦x≦0.7. but MFC for x=0.8 no longer showed a ferromagnetic increase with decreasing temperature. The increase in ferromagnetic magnetization with decreasing temperature at TC can be understood as a result of the mixed-valence state due to Co substitution. The negative magnetization observed in both samples, so-called the spin reversal, can be explained by the antiferromagnetic coupling of the Gd or Tm spin to the Mn and Co moments. We also investigated Gd1-yRyMn1-xCoxO3 and Tm1-yRyMn0.5Co0.5O3 (R: nonmagnetic rare-earth element) with substitution by nonmagnetic rare- earth elements La, Y, Lu. We can expect the chemical pressure effect due to the unit-cell volume (V) change by substituting Tm or Gd with nonmagnetic rare-earth elements. From Tm1-y(Y, Lu)yMn0.5Co0.5O3 observation we can obtained some remarkable structural details: owing to the ion radii, V of Tm1-yLuyMn0.5Co0.5O3 and Tm1-yYyMn0.5Co0.5O3 decreases and increases with increasing y, respectively; the parameter (a−c)/a, which is characterizes the orthorhombic distortion, continuously increases on Lu doping and decreases on Y-doping due to the substitution of Tm ions. Substitution of Tm with Y or Lu in orthorhombic Tm1-y(Lu, Y)yMn1-xCoxO3induces a systematic unit-cell volume change. This is the chemical pressure effect. From the magnetization measurement, we conclude that an increase of MFC and the unit-cell volume is responsible for the increase in transition temperature TC. We also studied the effects of chemical pressure with orthorhombic Gd1-yRyMn1-xCoxO3 (y = 0.1, 0.3, and 0.5). The substitution of Gd with La, Y, or Lu in Gd1-yRyMn1-xCoxO3 induced a systematic change in the unit-cell volume. Our results reveal that increasing or decreasing the average ionic radius of the rare-earth element in the compound affects the magnetic ordering temperature TC. The reduction in the proportion of Gd owing to substitution by nonmagnetic elements weakens the spin reversal effect.doctoral thesi