Budhy Kurniawan

Magnetization plateaus in NH4CuCl3

The magnetic susceptibility and high-field magnetization process of NH 4 CuCl 3 with double chains of CuCl 3 have been measured using single crystals. No anomaly indicative of the three-dimensional ordering is observed in susceptibility data above 1.7 K. It is found, by magnetization measurement down to 0.5 K, that in contrast to KCuCl 3 and TlCuCl 3 , NH 4 CuCl 3 has a gapless magnetic ground state at zero field. It is observed that the magnetization curve has two plateaus at one-quarter and three-quarters of the saturation magnetization, irrespective of the external field direction. The origin of the plateaus is attributed not to the magnetic anisotropy, but to the quantum effect. The relation between the plateaus and the period of the spin state is discussed in terms of a recent theory presented by Oshikawa et al . [Phys. Rev. Lett. 78 (1997) 1984].

Novel three-dimensional magnetic ordering in the quantum spin system NH4CuCl3

Low-temperature specific heat and magnetization measurements have been performed on the quantum spin system NH4CuCl3 which has magnetization plateaus at one-quarter and three-quarters of the saturation magnetization. It is found that the present system undergoes three-dimensional magnetic ordering at TN = 1.3 K. It is suggested that one-quarter of the spins are ordered below TN, and the remaining spins are in the singlet state. The small magnetic entropy at TN indicates that the phase transition occurs under the condition of a well-developed spin correlation around TN. The field dependence of the three-dimensional ordering is also investigated on the basis of magnetization measurements. Based on this evidence, a magnetic phase diagram for NH4CuCl3 is proposed.

Effect of Ca-Doping on the Structure and Morphology of Polycrystalline La0.7(Ba1-xCax)0.3MnO3 (x = 0; 0.03; and 0.05)

In this paper, we report structure and morphology of polycrystalline La0.7(Ba1-xCax)0.3MnO3 (x = 0; 0.03; 0.05). Basically, these materials are perovskite manganites type with the general structure AMnO3 (A= trivalent rare earth with divalent ion-doped) which have been extensively studied due to their interesting physical properties. It was known that the electron transport in this material influenced by ion doped at A site. Doping with different divalent ions should cause the lattice distortion. Hence, double exchange interaction is enhanced. In this study, we prepared our sample through the sol-gel method. It is show that the method has resulted in powder materials with ultra-fine particle size. The effect of Ca+2 and Ba+2 doping on the structure did not make any phase changing, but the lattice parameter of La0.7(Ba1-xCax)0.3MnO3 decreased below × = 0.03. Microstructure observed by scanning electron microscope to the sintered samples indicated that the microstructure is homogeneous with fine size of equiaxed grain morphology. Microanalysis by EDS confirmed there is no significant different between designated composition and measured one. It is concluded that effect of Ca+2 and Ba+2 doped in LaMnO3 has resulted in microstructural and lattice parameter changes. The doped materials are remaining single phase.

Magnetic hysterysis evolution of Ni-Al alloy with Fe and Mn substitution by vacuum arc melting to produce the room temperature magnetocaloric effect material

The development of magnetocaloric effect (MCE) material is done in order to reduce the damage of the ozone layer caused by the chlorofluorocarbons (CFCs) emitted into the air. The research dealing with synthesis of magnetocaloric materials based of Ni-Al Heusler Alloy structure and by varying substitution some atoms of Ni with Fe and Al with Mn on Ni-Al Heusler Alloy structure to become Ni44Fe6Mn32Al18. Vacuum Arc Melting (VAM) equipment is used to form the alloys on vacuum condition and by flowing argon gas atmosphere and then followed by annealing process for 72 hours. X-Ray Diffraction (XRD) reveals that crystallite structure of material is observed. We define that Ni44Fe6 as X2, Mn25 as Y, and Al18Mn7 as Z. Based on the XRD result, we observed that the general formula X2YZ is not changed. The PERMAGRAF measurement revealed that there exists of magnetic hysterysis. The hysterysis show that the magnetic structures of the system undego evolution from diamagnetic to soft ferromagnetic material which all o...

Formation of polycrystalline MgB2 synthesized by powder in sealed tube method with different initial boron phase

Magnesium diboride, MgB2 is a new high critical temperature superconductor that discovered in the beginning of the 21st century. The MgB2 has a simple crystal structure and a high critical temperature, which can be manufactured in several forms like thin films, tapes, wires including bulk in the large scale. For that reason, the MgB2 has good prospects for various applications in the field of electronic devices. In the current work, we have explored the synthesis of MgB2 polycrystalline using powder in a sealed tube method. Different initial boron phase for the synthesized of MgB2 polycrystalline were used. These were, in addition to magnesium powders, crystalline boron, amorphous boron and combination both of them were respectively fitted in the synthesis. The raw materials were mixed in a stoichiometric ratio of Mg: B=1:2, ground using agate mortar, packed into stainless steel SS304. The pack was then sintered at temperature of 800°C for 2 hours in air atmosphere. Phase formation of MgB2 polycrystalline in difference of initial boron phase was characterized using XRD and SEM. Referring to the diffraction pattern and microstructure observation, MgB2 polycrystalline was formed, and the formation was effective when using the crystalline Mg and fully amorphous B as the raw materials. The critical temperature of the specimen was evaluated by the cryogenic magnet. The transition temperature of the MgB2 specimen synthesized using crystalline magnesium and full amorphous boron is 42.678 K (ΔTc = 0.877 K).Magnesium diboride, MgB2 is a new high critical temperature superconductor that discovered in the beginning of the 21st century. The MgB2 has a simple crystal structure and a high critical temperature, which can be manufactured in several forms like thin films, tapes, wires including bulk in the large scale. For that reason, the MgB2 has good prospects for various applications in the field of electronic devices. In the current work, we have explored the synthesis of MgB2 polycrystalline using powder in a sealed tube method. Different initial boron phase for the synthesized of MgB2 polycrystalline were used. These were, in addition to magnesium powders, crystalline boron, amorphous boron and combination both of them were respectively fitted in the synthesis. The raw materials were mixed in a stoichiometric ratio of Mg: B=1:2, ground using agate mortar, packed into stainless steel SS304. The pack was then sintered at temperature of 800°C for 2 hours in air atmosphere. Phase formation of MgB2 polycrystalline...

Influence of intermetallic Fe and Co on crystal structure disorder and magnetic property of Ni50Mn32Al18 Heusler alloy

This works reports a study on structure and magnetic properties influenced by both Fe and Co on Ni50Mn32Al18 Heusler alloy as a candidate of magnetocaloric effect (MCE) materials. The Ni-Fe-Mn-Co-Al sample was prepared by arc melting furnace (AMF) in high purity argon atmosphere. X-ray diffraction investigation and magnetic hysteresis were conducted to characterize the synthesized sample. X-ray diffraction using Cu-Kα pattern shows that both Fe and Co introduce a tungsten type disorder of Ni50Mn32Al18 Heusler alloy which partially replace the site position of Ni and Mn respectively. However, in this tungsten type disorder, it is difficult to distinguish the exact position of each constituent atom. Therefore, we believe it may allow any exchange interaction of each electron possessed the atom. Interestingly, it produced a significant increase in the value of the hysteresis magnetic saturation.

Study of La0.67Sr0.33MnO3 Structure and Resistivity Synthesized by Using Sol Gel Method

In this study a colossal magnetoresistance La0.67Sr0.33MnO3 material was synthesized by using a sol gel method with different treatment heating process. First sample calcined at 850°C for 10 hours and pelletized, labelled as LSMO1, while another sample calcined at 850°C for 10 hours, pelletized, and sintered at 1200°C for 2 hours, labelled as LSMO2. The aim of this study was to learn a structure and resistivity of this material. The XRD results showed that both samples were single phase with no peak of impurity and formed a rhombohedral structure with space group R-3c. And the result showed that LSMO1 has smaller crystallite size than LSMO2. Result of resistivity measurement showed that LSMO1 has insulator behavior with resistivity several order of magnitude bigger than LSMO2. While LSMO2 had the peak of resistivity that showed a metal-insulator transition.

Magnetic Field- and Pressure-Induced Quantum Phase Transitions in NH4CuCl3

Quantum antiferromagnet NH 4 CuCl 3 shows magnetization plateaus at 1/4 and 3/4 of the saturation magnetization. Specific heat measurements at ambient pressure and magnetization measurements under hydrostatic pressure were performed on NH 4 CuCl 3 in magnetic fields. From specific heat measurements, we obtained the detailed magnetic phase diagram below 9 T, which includes the lower edge field H c1 of 1/4 plateau. The phase boundary just below H c1 can be described by a power low, H c1 - H N (T) T Φ with Φ = 2, where H N (T) is the transition field at temperature T. Magnetic susceptibility measurements under pressure revealed reentrant quantum phase transitions, such that the gapless ground state at zero field changes into gapped state with increasing pressure, and further into gapless state again.

Critical exponent analysis of lightly germanium-doped La0.7Ca0.3Mn1-xGexO3 (x = 0.05 and x = 0.07)

We have used a critical behavior study of La0.7Ca0.3MnO3 (LCMO) manganite perovskites whose Mn sites have been doped with Ge to explore magnetic interactions. Light Ge doping of 5 or 7 percent tended to produce LCMOs with second order magnetic transitions. The critical parameters of 5- and 7-percent Ge-doped LCMO were determined to be TC = 185 K, β = 0.331 ± 0.019, and γ = 1.15 ± 0.017; and TC = 153 K, β = 0.496 ± 0.011, and γ = 1.03 ± 0.046, respectively, via the modified Arrott plot method. Isothermal magnetization data collected near the Curie temperature (TC) was split into a universal function with two branches M(H,e) = |e|βf±(H/|e|β+γ), where e=(T–TC)/TC is the reduced temperature. f+ is used when T>TC, while f is used when T<TC. Such results demonstrate the existence of ferromagnetic short-range order in lightly Ge-doped LCMOs. Notably, doping with Ge at high concentrations tends to generate long-range ferromagnetic order.

Soft ferromagnetic properties of Ni44Fe6Mn32Al18 doped Co partially

Research in finding suitable magnetocaloric material around room temperature made ferromagnetic (FM) (Ni–Mn)-based Heusler alloys receive considerable attention as a potential candidate for the magnetic refrigerator. This compound are associated with the shape-memory effect, magnetic superelasticity, and more others magneto-functional properties. The compounds were prepared by vacuum arc melter (VAM) under argon atmosphere which sintering and annealing process were running with quartz cube in vacuum condition. A small amount of coercivity value at σ = 0 in the hysteresis curve occurred whereas magnetization of the sample in various temperature does not reach saturation. The Currie temperature Tc of the sample was obtained at 358 K. Nevertheless, this is dubious value because at T = 300 K the curves had swooped down. Additional measurements necessary to taken as a comparison to verify this value.