Structure, Magnetic, and Transport Properties of Ti-substituted La₀.₇Sr₀.₃MnO₃

Ti-substituted perovskites La0.7Sr0.3Mn1-xTixO3 with 0 ≤ x ≤ 0.20, were investigated by neutron diffraction, magnetization, electric resistivity, and magnetoresistance (MR) measurements. All samples show a rhombohedral structure (space group R3c) from 10 K to room temperature. At room temperature, the cell parameters a,c and the unit cell volume increase with increasing Ti content. However, at 10 K, the cell parameter a has a maximum value for x = 0.10, and decreases for x \u3e 0.10, while the unit cell volume remains nearly constant for x \u3e 0.10. The average (Mn,Ti)-O bond length increases up to x = 0.15, and the (Mn,Ti)-O-(Mn,Ti) bond angle decreases with increasing Ti content to its minimum value at x = 0.15 at room temperature. Below the Curie temperature TC, the resistance exhibits metallic behavior for the x ≤ 0.05 samples. A metal (semiconductor) to insulator transition is observed for the x ≥ 0.10 samples. A peak in resistivity appears below TC for all samples, and shifts to a lower temperature as x increases. The substitution of Mn by Ti decreases the 2p-3d hybridization between O and Mn ions, reduces the bandwidth W, and increases the electron-phonon coupling. Therefore, the TC shifts to a lower temperature and the resistivity increases with increasing Ti content. A field-induced shift of the resistivity maximum occurs at x ≤ 0.10. The separation of TC and the resistivity maximum temperature Tp,max enhances the MR effect in these compounds due to the weak coupling between the magnetic ordering and the resistivity as compared with La0.7 Sr0.3MnO3

Structure, magnetic and transport properties of Ti-substituted La0.7Sr0.3MnO3

Ti-substituted perovskites, La0.7Sr0.3Mn1-xTixO3, with x between 0 to 0.20, were investigated by neutron diffraction, magnetization, electric resistivity, and magnetoresistance (MR) measurements. All samples show a rhombohedral structure (space group R3c) from 10 K to room temperature. At room temperature, the cell parameters a, c and the unit cell volume increase with increasing Ti content. However, at 10 K, the cell parameter a has a maximum value for x = 0.10, and decreases for x greater than 0.10, while the unit cell volume remains nearly constant for x greater than 0.10. The average (Mn,Ti)-O bond length increases up to x=0.15, and the (Mn,Ti)-O-(Mn,Ti) bond angle decreases with increasing Ti content to its minimum value at x=0.15 at room temperature. Below the Curie temperature T_C, the resistance exhibits metallic behavior for the x _ 0.05 samples. A metal (semiconductor) to insulator transition is observed for the x_ 0.10 samples. A peak in resistivity appears below T_C for all samples, and shifts to a lower temperature as x increases. The substitution of Mn by Ti decreases the 2p-3d hybridization between O and Mn ions, reduces the bandwidth W, and increases the electron-phonon coupling. Therefore, the TC shifts to a lower temperature and the resistivity increases with increasing Ti content. A field-induced shift of the resistivity maximum occurs at x less than or equal to 0.10. The maximum MR effect is about 70% for La0.7Sr0.3Mn0.8Ti0.2O3. The separation of TC and the resistivity maximum temperature Tmax enhances the MR effect in these compounds due to the weak coupling between the magnetic ordering and the resistivity as compared with La0.7Sr0.3MnO3.Comment: zip fil

Providing a Scalable Video-on-Demand System using Future Reservation of Resources and Multicast Communications

In a video-on-demand (VoD) system the user can select and play movies according to his/her own quality of service (QoS) requirements; upon receipt of the user request, a typical VoD system checks whether there are enough available resources to deliver the requested movie to the user's host. If the response is yes, the movie presentation can start; otherwise, a rejection is sent back to the user; this means that the response is based only on the system's load at the time the request is made and assumes that the service duration (movie length) is infinite. In this paper we propose a scalable VoD (SVoD) system which decouples the starting time of the service from the time the service request is made and requires that the duration of the requested service must be specified. In response to a user request, SVoD determines the QoS with which the movie can be presented at the time the service request is made, and at certain later times carefully chosen. As an example, if the requested QoS cann..

Magnetic properties of Th3P4-type Tb4Sb3-X{Si, Ge, Bi}(X) solid solutions

International audienceThe magnetic properties of Tb4Sb2Bi, Tb4Sb2.75Ge0.25 and Tb4Sb2.3Si0.7 solid solutions (Th3P4-type, cubic; cI28, space group I (1) over bar 3d, No. 220) have been investigated by means of magnetization and neutron diffraction studies. The magnetization measurements indicate that the Tb4Sb2Bi compound orders magnetically at 120 K (T-N) and 50 K (T-C). The magnetization vs. field isotherm at 5 K shows signature of ferromagnetic order. Neutron diffraction experiment in zero applied magnetic field shows that below T-N = 125(4) K Tb4Sb2Bi exhibits a antiferromagnetic flat spiral type ordering with wave vector K-1 = [+/- K-X, +/- K-X, +/- K-X] (K-X value changes from 0.1033 up to 0.158 in the temperature interval down to 2 K). Below T-m = 70(4) K the decreasing of antiferromagnetic component coincides with increasing of the ferromagnetic component and about T-CN = 55(4) K, Tb4Sb2Bi shows ferromagnetic transition. At 2 K, the magnetic structure of Tb4Sb2Bi is ferromagnetic cone and the cone axis is along [1 1 1] direction. Neutron diffraction study of Tb4Sb2.75Ge0.25 indicate an antiferromagnetic ordering at 155(4) K (ferromagnetic cone with K-1 = [+/- 0.136(2), +/- 0.136(2), +/- 0.136(2)]) and ferromagnetic ordering (sharp increasing of ferrornagnetic component) at 145(4) K. The K-X value is nearly constant from 155 K down to 2 K. At 2 K, the magnetic structure of Tb4Sb2.75Ge0.25 is ferromagnetic cone with a weak antiferromagnetic component and the cone axis is along [1 1 1] direction. Low field magnetisation measurements on Tb4Sb2.3Si0.7 indicate a ferromagnetic ordering at T-C similar to 180 K. Thus small substitutions of Bi, Ge and Si at Sb-site of Tb4Sb3 are found to increase the magnetic ordering temperature of the parent compound

Phase separations in La<SUB>0.7-x</SUB>Dy<SUB>x</SUB>Ca<SUB>0.3</SUB>Mn(Fe)O<SUB>3</SUB>

Mossbauer spectroscopy of La0.7-xDyxCa0.3Mn(Fe)O3 shows phase separation, both above and below TC. The behavior in the two regions are independent and related to different phenomena. Above TC, the phase splitting is due to different lattice distortions. In one of the phases, Jahn-Teller distortion is significant. Below TC, the spin orderings in the two phases are ferromagnetic (FM) and spin glass (SG) orderings, respectively. At low temperatures, SG phase converts into FM phase when the applied magnetic field increases, but only partially. We find a drastic increase in magnetoresistivity (MR) as x is increased beyond 0.07. It attains a maximum value for x&#8776;0.12 (greater than750 000%) and decreases again rapidly as x increases. We have provided an explanation for the high MR in x=0.12 phase. Other differences between the compositions studied here can also be identified. First, the phase with Jahn-Teller distortion disappears when the temperature is lowered to TC in a composition with x 0.12. This is not the case when x=0.07. Second, we observe anomalous hysteresis loop when x=0.12. The anomaly is less pronounced in other compositions. Third, in composition x=0.07, the hyperfine magnetic fields (Hint) in FM and SG components are distinctly different. This is not so when x=0.12

Fingerprint of phase transition across the magnetic compensation temperature in Pr_1-xGd_xAl₂ alloys

The magnetization compensation phenomenon is observed for Sm1-xNdxScGe at x=0.09 at a temperature &#8764;90 K in a small applied magnetic field, which establishes the &#8216;spin surplus&#8217; status of magnetic moment of Sm in the host matrix. We also noted that the sample profiles in QD SQUID magnetometer become asymmetric in some situations indicating significant contributions from multiple moments higher than the dipole moment. We have successfully accounted for them using a fitting procedure the higher order magnetic moments

Problems of using femtocells in public cellular networks / Femtocelių naudojimo problematika mobiliojo ryšio tinkluose

This paper analyses the use of femtocells connected into a single macro network infrastructure. Different problems and possible solutions were discussed. The paper is focused on two separate benefits, which HNB could bring an operator and user. Femtocells are especially appealing due to the freedom of installation, increased macro network capacity, femto zone rates and etc. They provide users with better service quality, including voice service and higher throughput; while operators can reduce their network deployment expenditures. On the other hand, unplanned deployment, mobility issues and different types of user groups can cause a headache both for operators and customers. The analysis demonstrated that the majority of features of femtocells from the operator’s point of view were positive. Looking from the user’s point of view, most of shortcomings are difficult to remove. Positive and negative features both for operators and clients are presented in the HNB model. Santrauka Darbe nagrinėjami femtocelių naudojimo, jungiant jas į bendrą makrotinklo infrastruktūrą, klausimai. Analizuojami kylantys sunkumai ir jų sprendimo variantai. Išskiriamos dvi: vartotojų bei operatorių – šakos, kuriose analizuojama femtocelių teikiama nauda. Lengvas diegimas, tinklo talpumo didinimas, naujų femtozonų atsiradimas. Visa tai femtoceles daro patrauklias šiandieniam naudojimui tinkluose. Vartotojo požiūriu užtikrinama balso skambučių kokybė, didelis duomenų pralaidumas. Be to, operatorius turi galimybę plėsti tinklą daug mažesnėmis sąnaudomis. Neplanuoto diegimo principai, mobilumas, skirtingo tipo vartotojų grupės gali sukelti didelių sunkumų vartotojui naudojantis femtocele, o operatoriui užtikrinti tinkamą jų funkcionavimą. Atlikta femtocelių savybių analizė rodo, kad operatoriaus požiūriu didžioji dalis HNB savybių yra teigiamos. Iš kliento pozicijos pasireiškiantys trūkumai šalinami sunkiai. Teigiamų ir neigiamų savybių pasiskirstymas operatoriaus ir kliento šakoms pateikiamas HNB modeliu. Reikšminiai žodžiai: femtocelė, HNB, UMTS, LTE, interferencija, CSG

Magnetic compensation by Nd doping in SmScSi

The Sm intermetallic compound SmScSi, a ferromagnet with an unusually high Tc of 270 K, has been driven into a 'zero magnetization'state by substituting 9 at.% of Sm by Nd. The magnetic characteristics have been studied by dc magnetization, ac susceptibility and specific heat measurements and comparisons are made with the Gd doped SmAl2 systems

New features in rare earth based zero magnetization spin ferromagnets

A ferromagnetic rare earth (RE) intermatallic can be made to imbible zero magnetization characteristic and display magnetic reorientation phenomenon by letting a RE site be occupied at random by two RE atoms belonging to different halves of 4f series (Gd to be counted alongwith second half) and choosing their fractional compositions appropriately. In recent times, H. Adachi and co-workers drew specific attention to ferromagnetic Sm based systems, where the net moment can be either &#8216;orbital surplus&#8217;, or &#8216;spin surplus&#8217; (due to admixture effects) and the zero magnetization state can be obtained by substitution of Sm by the Gd or Nd. We present here a status report of our investigations and describe newer features related to magentic compensation phenomenon in a wide variety of RE system. In particular, our studies reveal that (i) the notion of spin flip transition across the temperature region of magnetic compensation is a generic behavior, (ii) it can happen in a re-entrant manner in specific circumstances, (iii) it survives strong hybridization effects that can happen for Ce3+ ions, e.g., in CeRh3B2, and compromise ferromagnetic exchange interaction between diddimilar RE spins, etc