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Abstrak :
Telah dilakukan sintesis bahan magnetik La0.67Ca0.33MnO3 (LCMO) serta La0,7(Ba1-xCax)0,3MnO3 x = 0,01; 0.03; 0.05 (LBCMO) dengan metode reaksi padatan untuk kemudian dilihat pengaruhnya terhadap parameter kisi, sifat magnetoresistansi, serta efek magnetokalorik. Karakterisasi XRD menunjukkan bahwa seluruh sampel memiliki fasa tunggal dan pergeseran puncak terdeteksi akibat penambahan doping kalsium. Pengujian resistivitas di bawah medan magnet menunjukkan bahwa resistivitas meningkat dengan bertambahnya doping kalsium. Selain itu penambahan doping kalsium mengakibatkan pergeseran temperatur transisi metal-insulator (Tp) menuju region temperatur yang lebih rendah. Selain itu, penambahan doping kalsium mengakibatkan bervariasinya nilai rasio magnetoresistansi. Studi magnetokalorik dilakukan dengan menggunakan metode Xiong[6]. Kurva magnetokalorik dari sampel tidak menunjukkan trend yang tepat, karena perbedaan jenis bahan yang digunakan pada penelitian ini (polikristal) dengan penelitian referensi (epitaxial thin film). ......Magnetic materials La0.7(Ba1-xCax)0.3MnO3 x = 0.01 - 0.05 (LBCMO) has been syntesized using solid state reaction method in order to find the relations between doping agent Calcium and the perovskite's lattice, magnetoresistance and magnetocaloric effect. A characterization using X-Ray Diffractometer shows that all of the samples have single phase pattern with several peak shifts detected as the influence of increasing the doping content. A resistivity measurement under influence of magnetic field shows that the resistivity increases and the metal - insulator transition temperatur (Tp) shifted into lower temperatur region. In other case, introducing calcium dopant into the main compound LBMO also give the effect of variation in magnetoresistance ratio. Magnetocaloric study was carried by using Xiong's method[6]. Magnetocaloric's curve of the samples shows its inacuraccy in its trend because the sample for this research (polycrystalline) and reference's sample (epitaxial thin film) was different.

Abstrak :
Telah dilakukan penelitian sifat resistansi dan hubungannya dengan efek magnetoresistanpada bahan perovskit La0,67Ba0,33MnO3 (LBMO) dan La0,7(Ba1-xCax)0,3Mn0,975Ni0,025O3 (x=0,01;0,03;0,05). Bahan uji disintesis dengan menggunakan solid state reaction. Variasi temperatur sintering pada LBMO tidak merubah parameter kisi. Sedangkan variasi dopan pada LBCMNiO dapat mengubah parameter kisi. Pengukuran sifat resistivitas dan sifat magnetoresistan bahan menunjukkan hasil yang berbeda. Karakterisasi menggunakan X-ray diffraction menunjukkan bahwa bahan uji memiliki fasa tunggal pada setiap variasi. Dari pengujian resistivitas di bawah pengaruh medan magnet menunjukkan bahwa variasi suhu sinter dan dopan menghasilkan perbedaan sifat resistivitas yang sangat signifikan. Variasi sinter yng lebih besar dan penambahan dopan kalsium dan nikel dengan komposisi lebih banyak dapat menurnkan resistivitas dan menggeser puncak resistiitas ke arah temperatur ruang serta menaikkan rasio magnetoresistansi mencapai -10% di bawah medan magnet 20.000 gauss. Pendekatan magnetokalorik menghasilkan nilai perubahan entropi yang bervariasi pada tiap sampel uji baik LBMO maupun LBCMNiO.

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A research has been conducted to investigate the resistivity behavior and it?s relation with magneto-resistance effect on perovskite materials which are La0.67Ba0.33MnO3 (LBMO) and La0.7(Ba1-xCax)0.3Mn0,975Ni0,025O3 (x=0.01;0.03;0.05). The samples were synthesized using solid state reaction. The sintering temperature variation on LBMO does not change its lattice parameter and doping variation on LBCMNiO has the lattice parameter. Different result was observed for resistivity and mangneto-resistancy properties of the materials. Characterization using x-ray diffraction showed that the samples have single phase on each variation. The resistivity measurement under the influence of magnetic field showed that the temperature variation of sintering and doping resulted in the significant differences of resistivity property. A higher sintering variation and the higher addition of Calcium & nickel as doping, decreased the resistivity and shifted the peak of resistivity to near room temperature and increased the ratio of magneto-resistance until -10% under magnetic field 20,000 gauss. A magnetocaloric approach resulted varied entropy change for each sample.