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"ABSTRAKTelah dilakukan penelitian mengenai karakteristik magnetoresistansi dan efek magnetokalorik (MCE) material La0,7(Ba1-xCax)0,3MnO3 (x = 0; 0,01; 0,03; 0,05; 1). Material La0,7(Ba1-xCax)0,3MnO3 termasuk ke golongan perovskite manganites dengan struktur umum AMnO3 (A = logam tanah jarang trivalen dengan dopan ion divalen seperti Sr, Ba, Ca, dsb). Rietveld analysis hasil karakterisasi XRD menunjukkan bahwa La0,7(Ba1-xCax)0,3MnO3 memiliki fasa tunggal dengan struktur kristal rhombohedral dan space group R-3c. Dengan uji semi-kuantitatif EDX telah dikonfirmasi kemurnian dari keseluruhan sampel ini. Meningkatnya konsentrasi doping Ca pada La0,7Ba0,3MnO3 menyebabkan terjadinya distorsi kisi sehingga akan mempengaruhi proses transfer elektron yang terjadi. Akibatnya, akan mempengaruhi sifat listrik, magnetoresistansi, dan magnetoklaorik sampel. Nilai rasio magnetoresistansi (MR) dari La0,7(Ba1-xCax)0,3MnO3 cukup tinggi yaitu ~30%.

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ABSTRACT

The characteristic of magnetoresistance and magnetocaloric effect (MCE) of La0,7(Ba1-xCax)0,3MnO3 (x = 0; 0,01; 0,03; 0,05; 1) materials are reported. La0,7(Ba1-xCax)0,3MnO3 material included in perovskite manganites family. Perovskite manganites have general structure AMnO3 (A = trivalent rare earth with divalent ion-doped such as Sr, Ba, Ca, etc). Rietveld analysis from XRD measurement confirmed that all samples are single phased. Semi-quantitative EDX analysis technique confirmed that all samples have compositional purity. Increasing of Ca dopant caused lattice distorsion and will influencing electron transport process in this samples. Hence, it will impact to electrical properties, magnetoresistance, and magnetolaric properties in this samples. La0,7(Ba1- xCax)0,3MnO3 material has magnetoresistance ratio ~30%."

"The change of the electric and magnetic properties due to the particle size effect has been reported recently and opened a new door to investigate phenomena driven by dimensional effects. One of the interesting examples is nanogold which is a weak diamagnetic in a bulk state but it becomes ferrimagnetic when the size of the Au cluster is around 3 nm. In the case of the Mott insulating system, it is reported that the magnetic transition temperature, TN, drastically decreased due to nano-sized effects. The reason for the appearance of the ferrimagnetic phase and the reduction in TN are not fully understood and still an open question. We investigated nano-sized effects in typical Mott insulator, La2CuO4, and in high-Tc superconductor cuprates, La2-xSrxCuO4. From muon spin relaxation (μSR) measurements, it is observed that the TN drastically decreased to be 47(12) K with reducing the particle size of La2CuO4 down to 24 nm. The phase separation of long-range and short-range magnetic ordering state was observed. We proposed a core-shell model to describe it. Particle size affects the magnetic interaction in La2CuO4 where the inter-plane magnetic interaction, J’, plays an important role in controlling TN of antiferromagnets. In the case of La1.80Sr0.20CuO4, we found that there is a strong suppression of the superconducting state and the appearance of weak magnetism induced by nano-sized effects. These results revealed that magnetic orders and superconductivity are intertwined and interconnected in high-Tc cuprate superconductors.

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Perubahan sifat listrik dan magnet yang disebabkan efek ukuran partikel telah diteliti secara intensif akhir-akhir ini dan membuka pandangan baru dalam investigasi fenomena yang di-drive oleh efek dimensi. Salah satu contoh efek partikel yang sangat menarik adalah nano-gold. Gold (Au) bersifat dimagnetik lemah dalam keadaan bulk tetapi menjadi ferrimagnetik saat ukuran cluster Au dikecilkan menjadi 3 nm. Di kasus sistem Mott insulating, suhu transisi magnetik, TN, dilaporkan menurun karena nano-sized effects. Alasan munculnya fasa ferrimagnetik dan menurunnya TN di sistem nano masih belum dipahami sepenuhnya dan masih menjadi pertanyaan. Kami menginvestigasi nano-sized effects di typical Mott insulator, La2CuO4, dan high-Tc superconductor cuprates, La2-xSrxCuO4. Dari hasil pengukuran muon spin relaxation (μSR), dihasilkan bahwa TN menurun drastis menjadi 47(12) K dengan dikecilkannya ukuran partikel menjadi 24 nm. Dari hasil μSR, teramati juga adanya pemisahan fasa antara long-range dan short-range magnetic ordering. Core-shell model diajukan untuk menjelaskan pemisahan fasa magnetic ordering yang terjadi di La2CuO4 nanopartikel. Kami menemukan bahwa inter-plane magnetic interaction, J’, berperan penting dalam mengontrol perubahan TN di antiferromagnet. Pada kasus La1.80Sr0.20CuO4, teramati adanya penurunan superconducting state secara drastis dan munculnya weak magnetism yang disebabkan oleh nano-sized effects. Hasil ini menunjukkan bahwa magnetic orders dan superkonduktivitas saling terkait dan berhubungan."