Hasil Pencarian  ::  Simpan CSV :: Kembali

Abstrak :
Material polikristalin La0,8-xKxBa0,05Sr0,15MnO3 (x = 0 dan 0,05) telah berhasil disintesis menggunakan metode sol-gel. Analisis hasil karakterisasi X-Ray Diffractometer (XRD) menunjukkan bahwa material La0,8-xKxBa0,05Sr0,15MnO3 (x = 0 dan 0,05) yang telah disintesis merupakan material fasa tunggal dengan struktur rhombohedral dan space group R-3c. Hasil karakterisasi XRD juga diperkuat oleh hasil karakterisasi Energy Dispersive X-ray (EDX) dan X-ray Photoelectron Spectroscopy (XPS) yang telah menunjukkan bahwa semua jenis senyawa kimia yang terdapat pada material La0,8-xKxBa0,05Sr0,15MnO3 (x = 0 dan 0,05) merupakan senyawa yang diinginkan. Observasi morfologi menggunakan Scanning Electron Microscope (SEM) menujukkan bahwa substitusi ion potasium berdampak pada terjadinya perbesaran ukuran grain. Karakterisasi Magnetic Properties Measurement System (MPMS) menunjukkan bahwa substitusi ion potasium menyebabkan terjadinya peningkatan temperatur Curie dari 320 K, untuk nilai x = 0, menjadi 335 K, untuk nilai x = 0,05. Peningkatan ini disebabkan karena menguatnya interaksi double-exchange pada sampel dengan nilai x = 0,05. Substitusi ion potasium juga berdampak pada terjadinya peningkatan nilai perubahan entropi magnetik (A𝑆𝑀) dan nilai Low Field Magnetoresistance (LFMR). Nilai −Δ𝑆𝑀 material La0,8-xKxBa0,05Sr0,15MnO3 (x = 0 dan 0,05) meningkat dari 4,21 J/kg K menjadi 4,98 J/kg K pada medan magnet eksternal lima Tesla. Sementara itu, nilai LFMR mengalami peningkatan dari 9% menjadi 14% pada medan magnet eksternal satu Tesla. Berdasarkan hasil analisis perilaku kritis dari material La0,8-xKxBa0,05Sr0,15MnO3 (x = 0 dan 0,05) dapat disimpulkan bahwa substitusi ion potasium mempengaruhi perilaku kritis dari material La0.8-xKxBa0,05Sr0,15MnO3 (x = 0 dan 0,05). Hal ini dibuktikan dengan berubahnya nilai parameter kritis dari material tersebut. Nilai parameter kritis untuk x = 0 adalah 𝛽 = 0,248; 𝛾 = 1,048; dan 𝛿 = 3,342 sedangkan nilai parameter kritis untuk x = 0,05 adalah 𝛽 = 0,226; 𝛾 = 1,183; dan 𝛿 = 4,518. Karakterisasi ESR menunjukkan adanya fasa magnetik yang tidak homogen pada material La0,8-xKxBa0,05Sr0,15MnO3 (x = 0 dan 0,05). Keberadaan fasa magnetik yang tidak homogen ini merupakan bukti terjadinya fenomena phase separation yang berkorelasi kuat terhadap terjadinya peningkatan nilai A𝑆𝑀 dan nilai LFMR.

---

Exploration on the magnetic properties of polycrystalline La0.8-xKxBa0.05Sr0.15MnO3 (x = 0 and 0.05) manganite have been reported. The samples have been synthesized using sol-gel method. Powder diffraction analysis shows that both samples crystallized in rhombohedral structure with R-3c space group. Furthermore, rietveld refinement analysis proves that the obtained samples are single phase, without any detectable impurities. This argument is also supported by the characterization result from Energy Dispersive X-ray (EDX) and X-ray Photoelectron Spectroscopy (XPS). Morphological observation using Scanning Electron Microscope (SEM) shows that potassium substitution increases the average grain size of the studied samples. Magnetization measurement with respect to temperature shows that the curie temperature (𝑇𝐶) of sample with potassium ion is larger compared to the undoped sample. The reported 𝑇𝐶 was be 320 and 335 K for x = 0 and x = 0.05, respectively. Detailed inspection upon the magnetocaloric property of the samples shows that potassium substitution increases the magnetic entropy change (A𝑆𝑀) of the sample. The reported −Δ𝑆𝑀 value was 4.21 and 4.98 J/kg K for x = 0 and x = 0.05, respectively. It was found that both samples exhibit a Low Field Magnetoresistance (LFMR) phenomenon at low temperature and low external magnetic field (< 1T). Moreover, potassium substitution increases the estimated LFMR value from 9 to 14% for x = 0 and x = 0.05, respectively. The analysis on the critical behavior of both samples shows that potassium substitution affects the critical behavior of the studied samples. This is shown by the different critical parameters for each sample. The reported critical parameter for x = 0 are 𝛽 = 0.248; 𝛾 = 1.048; 𝛿 = 3.342 and the critical parameters for x = 0.05 are 𝛽 = 0.226; 𝛾 = 1.183; and 𝛿 = 4.518. Electron Spin Resonance (ESR) characterization reveals that there is a presence of magnetic inhomogeneity inside both samples. The presence of magnetic inhomogeneity suggests that both samples exhibit a phase separation phenomenon. This phenomenon is believed to greatly influence the increase of A𝑆𝑀 and LFMR value in the studied samples.

Abstrak :
ABSTRAK
Paduan Heusler Ni-Mn-Sn adalah salah satu material yang menjadi perhatian banyak peneliti, karena memiliki potensi menghasilkan Magnetocaloric Effect (MCE) terutama dalam penerapan berbagai aplikasi bidang magnetik. Pada penelitian ini telah dilakukan sintesis polikristalin Ni43Mn41Co5Sn11 menggunakan teknik vakum peleburan busur panas atau vacuum arc melting (VAM) pada temperatur tinggi dalam suasana kaya gas argon. Optimalisasi sifat magnetik paduan NMCS dilakukan pada temperatur 1173 K dengan variasi waktu anil selama 0, 6, 12, dan 24 jam hingga didapatkan fasa kristal yang homogen. Pola difraksi sinar-X pada sampel hasil anil terdiri dari fasa martensit dan austenit, dengan struktur kristal FCC pada temperatur ruang. Fasa dendrit material pasca peleburan telah bertransformasi menjadi fasa yang seragam seiring dengan variasi waktu anil yang diberikan untuk mencapai homogenisasi. Hasil identifikasi struktur kristal material pasca anil 6 dan 12 jam menyerupai tipe order Cu2MnAl, sedangkan untuk material pasca anil 24 jam menyerupai tipe order CsCl. Adapun pembentukan fasa NiMnCoSn pada sampel melalui pembentukan fasa antara yakni Ni2MnSn. Apabila dilihat dari nilai temperatur curie material NMCS tidak mengalami perubahan secara signifikan seiring dengan variasi waktu anil yaitu sekitar 348~351 K, namun pada efek perlakuan anil selama 12 jam menunjukan nilai magnetisasi terbesar sekitar 57.96 emu/g dengan koersivitas 45.60 Oe. Hasil penelitian ini menyimpulkan bahwa sintesa material magnetokalorik paduan heusler Ni43Mn41Co5Sn11 melalui teknik peleburan vakum yang dilanjutkan dengan perlakuan anil selama 12 jam dapat menjadi salah satu cara dalam pembuatan material MCE berbasis paduan heusler

---

ABSTRACT
Ni?Mn?Sn Heusler alloys have been attracting alot of scientists by virtue of their magnetocaloric effect and application potential for magnetic refrigeration at room temperature. In this work, policrystalline Ni43Mn41Co5Sn11 alloy has been synthesized by vacuum arc-melting of pure elements under protective Ar atmosphere. The optimization of magnetic properties of the NMCS alloy was obtained during the annealing times at 1173 K by various annealing times 0, 6, 12, and 24 hours. X-ray diffraction patterns showed that the annealed samples were in the mixed martensite-austenite phase, revealed that the alloy has a FCC crystal structure as the main phase at room temperature. A result confirmed that the dendritic structure transformed into the uniform crystal structure of varying annealing time in order to attain homogeneous alloy. The crystal structure identification of the material after the annealing 6 and 12 hours showed Cu2MnAl order type, and the annealed material for 24 hours showed CsCl order type. The NiMnCoSn phase formation in a sample through a phase formation in the middle the Ni2MnSn. The curie temperature of the NMCS material was not change significantly during variation of annealing time around 348~351 K, but the effect of annealing for 12 hour showed the greatest magnetization value at 57.96 emu/g and also the coercivity at 45.60 Oe. The results of this study concluded that synthesis of heusler alloy Ni43Mn41Co5Sn11 through vacuum melting techniques, followed by annealing for 12 hours has proven to be alternative route for material MCE-based heusler alloys fabrication.

Abstrak :
Manganite perovskite has a wide variety of potential applications as an advanced material, for example, in magnetic random access memory, spintronics, magnetoelectric, magnetic field sensors and cooling technology, based on magnetism and magnetic materials. In work on cooling technology, magnetic materials show a magnetocaloric effect. Manganite perovskite has some fundamental properties, such as Curie temperature, magnetic entropy change, temperature span and relative cooling power. Current works report detailed properties of manganite perovskite in La0.7Ca0.3MnO3 doped with Cu, which show magnetocaloric effects. The samples were synthesized by a conventional solid state reaction. A small amount of doping Cu 1%~3% at a Mn site maintains the First-Order Magnetic Transition (FOMT) without leading into the Second-Order Magnetic Transition (SOMT). Maximum magnetic entropy change increased as the Cu-doped decreased. Introducing a small percentage of Cu-doped on La0.7Ca0.3Mn1-xCuxO3 also implies decreasing the Curie temperature, TC. For all samples under external application in a field of 10 kOe, these resulted in a slightly wider temperature span and the Relative Cooling Power (RCP) of about 39 J/kg to 47 J/kg as the Cu-doped decreased. The small amount of Cu-doping on La0.7Ca0.3MnO3 keeps the rate of relative cooling power in a wider temperature range. It may be beneficial for cooling technology based on magnetism and magnetic materials.

Abstrak :
Pada penelitian ini telah dipelajari efek metode sintesis terhadap fenomena magnetik material perovskite manganite La0,7Ba0,1Ca0,1Sr0,1MnO3 (LBCSMO). Sampel telah disintesis menggunakan metode Wet-Mixing (WM) dan Sol-Gel (SG) dengan temperatur kalsinasi dan sintering yang sama. Analisis X-Ray Difractometer (XRD) menunjukkan bahwa kedua sampel memiliki fasa tunggal dengan struktur Rhombohedral dan space group R-3c. Hasil Scanning Electron Microscopy (SEM) menunjukkan bahwa sampel WM memiliki ukuran grain yang lebih kecil dibandingkan sampel SG. Karakterisasi Energy Dispersive X-ray Spectroscopy (EDS) dengan metode elemental mapping mengonfirmasi homogenitas sampel. Karakterisasi X-Ray Photoemission Spectroscopy (XPS) juga mengonfirmasi elemen yang terkandung dari kedua sampel dengan terdeteksinya spektrum core level La 3d, Ba 3d, Ca 2p, Sr 3d, Mn 2p, dan O 1s. Metode sintesis yang berbeda menyebabkan perbedaan parameter struktur dan ukuran grain yang memengaruhi sifat magnetik sampel. Hal tersebut ditunjukkan oleh perbedaan karakteristik transisi fasa magnetik. Pada sampel WM terjadi slow magnetic transition dibandingkan sampel SG yang dibuktikan dari kurva transisi yang lebih landai. Perbedaan ini dapat dijelaskan dengan teori interaksi Double-Exchange (DE) dan model Core-Shell. Nilai temperatur Curie (𝑇𝐶) sampel WM dengan nilai 316 K sedangkan nilai sampel SG sebesar 330 K. Analisis critical behavior menggunakan metode Modified Arrott Plot (MAP), Kouvel-Fisher (KF), dan Critical Isotherm (CI) juga menunjukkan perbedaan nilai critical exponents (𝛽, 𝛾 dan 𝛿) sebagai akibat perbedaan metode sintesis. Nilai critical exponents sampel WM mendekati nilai model Mean-field theory (KF: 𝛽 = 0,476; γ = 1,029; 𝛿 = 3,096), sedangkan untuk sampel SG mendekati nilai model Tricritical mean-field (KF: 𝛽 = 0,262; 𝛾 = 1,165; 𝛿 = 5,447). Perbedaan metode sintesis juga memengaruhi nilai perubahan entropi magnetik (-∆𝑆𝑀) dan magnetoresistance sampel. Nilai -ΔSM pada medan magnet 𝜇0𝐻 = 5 T adalah 3,16 dan 4,89 J/kg.K untuk masingmasing sampel WM dan SG. Nilai Low Field Magnetoresistance (LFMR) pada nilai medan magnet 𝜇0𝐻 = 0,1 T sekitar 9,1 % untuk sampel SG pada temperatur 108 K dan 7,6 % untuk sampel WM pada temperatur 110 K. Karakterisasi electron spin resonance (ESR) menunjukkan bahwa transisi fasa magnetik juga dipengaruhi spin-lattice dan spinspin relaxation. Selain itu, karakterisasi ESR mengonfirmasi ketidakhomogenan medan magnetik lokal dan phase separation (PS) antara fasa feromagnetik dan paramagnetic. ......The effects of the synthesis method on the magnetic phenomenon of perovskite manganite La0.7Ba0.1Ca0.1Sr0.1MnO3 (LBCSMO) have been investigated. Samples were synthesized using the Wet-Mixing (WM) and Sol-Gel (SG) method with the same temperature of calcination and sintering. The X-Ray Diffraction (XRD) analysis showed that both samples had a single phase with a Rhombohedral structure with an R-3c space group. SEM characterization exhibited the grain size of the WM sample smaller than the SG sample. Energy Dispersive X-ray Spectroscopy (EDS) characterization with the elemental mapping method confirms the homogeneity of the sample. The results of XRay Photoemission Spectroscopy (XPS) characterization shows the core level spectrum of La 3d, Ba 3d, Ca 2p, Sr 3d, Mn 2p, and O 1s which confirms the elements contained in both samples. The different synthesis methods lead to different structure parameters and grain sizes which affect the magnetic properties of the samples. It is indicated by the difference in the characteristics of the magnetic phase transition. The WM sample shows a slow magnetic transition compared to the SG sample, which showed by a broaden transition curve. The different magnetic properties of both samples can be explained by Double-Exchange interaction and Core-Shell Model. The Curie temperature (𝑇𝐶) values for each sample were around 315 and 330 K for WM and SG samples, respectively. Critical behaviour analysis using the Modified Arrott plot (MAP), the Kouvel-Fisher (KF) method, and Critical Isotherm (CI) showed crossover critical exponent values (𝛽, γ, and 𝛿). The critical exponent values of the WM sample close to Mean-field theory (KF: 𝛽 = 0.476; 𝛾 = 1.029; 𝛿 = 3.096), whereas for the SG sample close to Tricritical mean-field model (KF: 𝛽 = 0.262; 𝛾 = 1.165; 𝛿 = 5.447). The different synthesis methods also affect the value of magnetic entropy change (-∆𝑆𝑀) and magnetoresistance. The estimated - ∆𝑆𝑀 at the magnetic field 𝜇0𝐻 = 5 T are 3.16 and 4.89 J/kg.K for WM and SG samples, respectively. Both samples showed Low Field Magnetoresistance (LFMR) phenomenon is 9.1% for the SG sample at 108 K and 7.6% for the WM sample at 110 K at the magnetic field 𝜇0𝐻 = 0.1 T. Electron spin resonance (ESR) characterization shows that magnetic phase transitions are also influenced by spin-lattice and spin-spin relaxation. ESR characterization also confirms the inhomogeneity of the local magnetic field and phase separation (PS) between the ferromagnetic and paramagnetic phase.

Abstrak :
Modern technology for refrigerators and coolers is based on the chemical gas Chlorofluorocarbon (CFC) compression method that is indicative of a high consumption of electricity. The CFC is also understood as a reason for global warming. One of the solutions to this issue is magnetic refrigeration technology, which is environmentally friendly because it does not use any hazardous chemicals or ozone depleting/greenhouse gases. Magnetic refrigeration technology is based on the magnetocaloric effect of magnetic refrigerant materials. Exploring the magnetocaloric effect of magnetic refrigerant materials is important because these contain many of the physical properties needed for magnetic refrigeration technology. Herein, the present work reports on the magnetocaloric effect of La0.7Ca0.3Mn1?xSnxO3 (x = 0.0, x = 0.02 and x = 0.04) compound samples produced with the solid state reaction technique. Curie temperature TC obtained for the La0.7Ca0.3Mn1?xSnxO3 (x = 0.0, x = 0.02 and x = 0.04) are 260 K, 176 K and 170 K with -?SM max of 4.32 J×kg-1×K-1, 1.61 J×kg-1×K-1 and 1.24 J×kg-1×K-1 and a refrigerant capacity of 48 J/kg, 41.43 J/kg and 28.53 J/kg for x = 0.0, x = 0.02 and x = 0.04, respectively. A small addition of Sn-doped resulted in a significant decrease of more than 80 K on the Curie temperature scale compared to that of La0.7Ca0.3MnO3. The large gap in the decreasing magnetic temperature phase transition might be useful as an option of metal/transition metal doped for tuning the Curie temperature of magnetic refrigerant materials.