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in subjects: "Curie Point"

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Role of intergrowths in the properties of the naturally layered manganites.

The structural and magnetic properties of the two-layered Ruddlesden-Popper phase SrO(La{sub 1{minus}x}Sr{sub x}MnO{sub 3}){sub 2} with x = 0.3 and x = 0.4 are investigated. These naturally layered manganites exhibit a colossal magnetoresistance, a magnetic anisotropy which is strongly composition-dependent, almost no remanence, and a non-vanishing magnetization in an extended temperature range above the Curie temperature (T{sub c}). The magnetization in this temperature range is not intrinsic … more

Date: October 27, 1998

Creator: Bader, S. D.; Berger, A.; Jiang, J. S.; Miller, D. J.; Mitchell, J. F. & Osgood, R. M., III

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Critical Behavior of Thermal Expansion and Magnetostriction in the Vicinity of the First order transition at the Curie Point of Gd5(SixGe1-x)4

Thermal expansion (TE) and magnetostriction (MS) measurements have been conducted for Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} with a series of x values to study its critical behavior in the vicinity of transition temperatures. It was found that the Curie temperature of Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} for x 0 {approx} 0.5 is dependent on magnetic field, direction of change of temperature (Tc on cooling was lower than Tc on heating), purity of Gd starting material, compositions, material pr… more

Date: December 19, 2004

Creator: Han, Mangui

Item Type: Thesis or Dissertation

Partner: UNT Libraries Government Documents Department

open access

Thermodynamic limits to the maximum Curie temperature in Ga1-xMnxAs

Using the ion channeling techniques we find that a substantial fraction (up to 15%) of the Mn atoms reside in interstitial sites in Ga{sub 1-x}Mn{sub x}As alloys (with x ranging from 0.02 to 0.09). Moreover, the T{sub C} of Ga{sub 1-x}Mn{sub x}As is found to be very sensitive to annealing at temperatures close to the growth temperature of 265 C. Ion channeling results demonstrate that the increase of TC after annealing at 282 C can be attributed to a relocation of Mn atoms from interstitial sit… more

Date: July 19, 2002

Creator: Yu, K.M.; Walukiewicz, W.; Wojtowicz, T.; Kuryliszyn, I.; Liu, X.; Sasaki, Y. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Structural and magnetic properties of MnAs nanoclusters formed by Mn ion implantation in GaAs

Ferromagnetic (FM) nanostructures embedded in semiconductors are of fundamental interest since their physical properties could be used in new devices such as memories, sensors or spintronics. In this work, we present results obtained on the synthesis and characterization of nanosized MnAs ferromagnets buried in GaAs. These nanocrystals are formed either by single Mn implantation or Mn + As co-implantation at room temperature into GaAs wafers at 141 and 180 keV respectively. Two doses, 1 x 10{su… more

Date: August 1, 2002

Creator: Serres, A.; Benassayag, G.; Respaud, M.; Armand, C.; Pesant, J.C.; Mari, A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Dielectric Properties and Depoling Characteristics of Pb(Zr(0.95)Ti(0.05))O(3) Based Ceramics: Near-Critical Grain Size Behavior

Chemically prepared Pb(Zr{sub 0.951}Ti{sub 0.949}){sub 0.982}Nb{sub 0.018}O{sub 3} ceramics were fabricated that were greater than 95% dense for sintering temperatures as low as 925 C. Achieving high density at low firing temperatures permitted isolation of the effects of grain size, from those due to porosity, on both dielectric and pressure induced transformation properties. Specifically, two samples of similar high density, but with grain sizes of 0.7 {micro}m and 8.5 {micro}m, respectively,… more

Date: September 30, 1999

Creator: Rodriguez, Mark A.; Scofield, Timothy W.; Tuttle, Bruce A.; Voigt, James A.; Yang, Pin & Zeuch, David H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

First-principles exchange interactions between ferro and antiferromagnetic films: Co on NiMn, a case study

Heisenberg exchange parameters at the interface of antiferromagnetic NiMn with ferromagnetic Co are calculated from first-principles. The authors use a layer version of the Korringa-Kohn-Rostocker multiple scattering approach and an expression, which is based on the expansion of the band energy, to calculate the exchange parameters from the underlying electronic structure. For bulk systems, the parameter sets yield Curie temperatures that are in good agreement with experimental values. In the i… more

Date: December 31, 1997

Creator: Schulthess, T. C. & Butler, W. H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Temperature compensation of NdFeB permanent magnets

Permanent magnet blocks of NdFeB have a relatively high maximum energy product. Because of its relatively low Curie temperature, however, NdFeB has a large temperature coefficient for its residual induction. The temperature coefficients of the relative magnetic fields ({Delta}B/B)/{Delta}T in the air gap of NdFeB dipole magnets were reduced from {minus}1.1 {times} 10{sup {minus}3}/c to less than 2 {times} 10{sup {minus}5}/{degree}C under operating temperatures of {+-} 6 C. This was achieved pas… more

Date: August 1, 1997

Creator: Kim, S. H. & Doose, C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Coherent coupling in ferroelectric superlattices

The phase transition and dielectric behavior of ferroelectric multilayers have been discussed. The coherent interaction between ultra-thin layers can be significantly strong, resulting in a broad diffuse phase transition. The thicknesses of layers and their spatial distributions hold the keys of enhancing dielectric properties in a broad temperature range.

Date: July 1, 1996

Creator: Li, S.; Eastman, J.A.; Vetrone, J.; Newnham, R.E. & Cross, L.E.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Electronic and magnetic properties of zincblende half-metal superlattices

Zincblende half-metallic compounds such as CrAs, with large magnetic moments and high Curie temperatures, are promising materials for spintronic applications. They explore layered materials, consisting of alternating layers of zincblende half-metals, by first principles calculations, and find that superlattices of (CrAs){sub 1}(MnAs){sub 1} and (CrAs){sub 2}(MnAs){sub 2} are half-metallic with magnetic moments of 7.0{mu}{sub B} and 14.0{mu}{sub B} per unit cell, respectively. They discuss the n… more

Date: November 5, 2003

Creator: Fong, C Y; Qian, M C; Pask, J; Yang, L H & Dag, S

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Imaging the First-Order Magnetic Transition in La0.35Pr0.275Ca0.375MnO3

The nature of the ferromagnetic, charge, orbital, and antiferromagnetic order in La{sub 0.35}Pr{sub 0.275}Ca{sub 0.375}MnO{sub 3} (LPCMO) on the nano and micro scale was investigated by photoemission electron microscopy (PEEM) and resonant elastic soft x-ray scattering (RSXS). The structure of the ferromagnetic domains around the Curie temperature T{sub C} indicates that they nucleate under a high degree of lattice strain, which is brought about by the charge, orbital, and antiferromagnetic ord… more

Date: May 1, 2012

Creator: Burkhardt, Mark

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

What Coexists with the Ferromagnetic Metallic Phase in Manganites?

Colossal magnetoresistance, whereby the application of a magnetic field reduces the resistivity of a manganite by orders of magnitude, is generally believed to occur because of coexisting phases. Development of a complete theory to explain the phenomenon requires that the exact nature of these phases be known. We used resonant elastic soft x-ray scattering to examine the superlattice order that exists in La{sub 0.35}Pr{sub 0.275}Ca{sub 0.375}MnO{sub 3} above and below the Curie temperature. By … more

Date: July 25, 2012

Creator: Burkhardt, Mark H.; Hossain, M.A.; Sarkar, S.; Achkar, A.J.; Hawthorn, D.G.; Sutarto, R. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

GALVANOMAGNETIC PROPERTIES OF URANIUM MONOSULFIDE

The magnetic and galvanomagnetic properties of US, including resistivity, magnetoresistance, and Hall effect, were studied. The resistivity was found to be approximately a hundred times higher in US than in the common ferromagnetic metals, but the temperature dependence of resistivity was similar, showing an abnormal decrease below the Curie point. The magnetoresistance of US was found to be negative with a sharp minimum at the Curie point. The study of the Hall effect revealed that two Hall co… more

Date: June 1, 1963

Creator: Kazmierowicz, Casimir W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Direct Observation of Field and Temperature Induced Domain Replication in Dipolar Coupled Perpendicular Anisotropy Films

Dipolar interactions in a soft/Pd/hard [CoNi/Pd]{sub 30}/Pd/[Co/Pd]{sub 20} multilayer system, where a thick Pd layer between two ferromagnetic units prevents direct exchange coupling, are directly revealed by combining magnetometry and state-of-the-art layer resolving soft x-ray imaging techniques with sub-100-nm spatial resolution. The domains forming in the soft layer during external magnetic field reversal are found to match the domains previously trapped in the hard layer. The low Curie te… more

Date: July 1, 2007

Creator: Hauet, T.; Gunther, C.M.; Pfau, B.; Eisebitt, S.; Fischer, P.; Rick, R. L. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Interplay between intrinsic and stacking-fault magnetic domains in bi-layered manganites

We present a low temperature X-ray photoemission electron microscopy study of the bi-layered manganite compound La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} (BL-LSMO) to investigate the influence of stacking faults, which are structurally and magnetically different from the bi-layered host. In BL-LSMO small magnetic moment persists to T* = 300K, well above the Curie temperature of 120K (T{sub C}). Our magnetic images show that 3D stacking faults are responsible for the T* transition. Furthermore, cl… more

Date: September 11, 2012

Creator: Hossain, M. A; Burkhardt, Mark H.; Sarkar, S.; Ohldag, H.; Chuang, Y. D.; Scholl, A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Magnetic, Caloric and Crystallographic Properties of Dy5(SixGe1-x)4 Alloys

Polycrystals of the intermetallic compound of the Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} system, where x = 0, 0.25, 0.5, 0.625, 0.675, 0.725, 0.75, 0.775, 0.825, 0.875, and 1, have been prepared by electric-arc-melting on water-cooled copper hearth in an argon atmosphere. A study of phase relationships and crystallography in the pseudobinary system Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} using X-ray powder diffraction data and optical metallography was completed. It revealed that silicides in th… more

Date: July 19, 2002

Creator: Ivchenko, Vitaliy Vladislavovich

Item Type: Thesis or Dissertation

Partner: UNT Libraries Government Documents Department

open access

Sign reversal of the MN-O bond compressibility in La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} below T{sub C}: Exchange striction in the ferromagnetic state

The crystal structure of the layered perovskite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} has been studied under hydrostatic pressure up to {approximately} 6 kbar, in the paramagnetic and ferromagnetic states, with neutron powder diffraction. The compressibility of the Mn-O apical bonds in the double layer of MnO{sub 6} octahedra changes sign from the paramagnetic insulator (PI) to the ferromagnetic metal (FM) state; in the Fm state the Mn-O-Mn linkage between MnO{sub 2} planes expands under appl… more

Date: March 1997

Creator: Argyriou, D. N.; Mitchell, J. F.; Chmaissem, O.; Short, S.; Jorgensen, J. D. & Goodenough, J. B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

PdMn and PdFe: New Materials for Temperature Measurement Near 2K

Interest in the critical dynamics of superfluid He in microgravity conditions has motivated the development of new high resolution thermometry technology for use in space experiments near 2K. The current material commonly used as the temperature sensing element for high resolution thermometers (HRTs) is copper ammonium bromide (Cu(NH{sub 4}){sub 2}Br{sub 4}2H{sub 2}O) or CAB, which undergoes a ferromagnetic phase transition at 1.8K. HRTs made from CAB have demonstrated low drift (<10fK/s) an… more

Date: February 1, 1999

Creator: Aselage, T. L.; Duncan, R. V.; Klemme, B. J.; Sergatskov, D. A.; Adriaans, M. J. & Day, P. K.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Extrinsic Curie temperature and spin reorientation changes in Nd{sub 2}Fe{sub 14}B/{alpha}-Fe nanocomposites

The Curie temperatures and spin reorientation temperatures of a series of four melt-spun nanocomposite materials comprised of Nd{sub 2}Fe{sub 1}4B and varying amounts of {alpha}-Fe were measured using independent techniques. The phase constitution and grain size was assessed with synchrotron x-ray diffraction; the Curie temperatures were measured by differential thermal analysis (DTA) and dc SQUID magnetometry in the temperature range 375 K {le} T {le} 800 K, whereas the spin reorientation tran… more

Date: May 1, 1998

Creator: Lewis, L.H. & Panchanathan, V.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Effects of dynamic Jahn-Teller distortions by Raman spectroscopy in the layered CMR manganite La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7}, x = 0.36

The close interplay among charge, spin, and lattice degrees of freedom in the colossal magnetoresistive (CMR) manganite oxides is believed to play an important role in the transport mechanism in these itinerant ferromagnets. While the work on CMR materials has concentrated on the 3D perovskite manganites, the discovery of the layered compounds La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} as another class of CMR oxides provides a rich opportunity to explore the relationship between structure … more

Date: December 1, 1998

Creator: Bordallo, H. N.; Argyriou, D. N.; Mitchell, J. F. & Strouse, G. F.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Polaron Coherence Condensation As the Mechanism for Colossal Magnetoresistance in Layered Manganites

Angle-resolved photoemission spectroscopy data for the bilayer manganite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} show that, upon lowering the temperature below the Curie point, a coherent polaronic metallic groundstate emerges very rapidly with well defined quasiparticles which track remarkably well the electrical conductivity, consistent with macroscopic transport properties. Our data suggest that the mechanism leading to the insulator-to-metal transition in La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{su… more

Date: November 20, 2007

Creator: Mannella, N.; Yang, W. L.; Tanaka, K.; Zhou, X. J.; Zheng, H.; Mitchell, J. F. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Preparation, crystallography, magnetic and magnetothermal properties of Ce5SiGe4-x alloys

An investigation of the crystal structure and the phase relationships in the Ce{sub 5}Si{sub 4-x}Ge{sub x} system has been carried out. The crystal structures of the single phase intermetallics were characterized using X-ray powder diffraction and subsequent refinement employing the Rietveld analysis technique was performed. The intermetallic system was found to crystallize in three distinct crystal structures. The Ce{sub 5}Si{sub 4}-based solid solution extends from x = 0 to x = 2.15 and it wa… more

Date: May 1, 2005

Creator: Vijayaraghavan, Rangarajan

Item Type: Thesis or Dissertation

Partner: UNT Libraries Government Documents Department

open access

Magnetic Contribution to Heat Capacity and Entropy of Nicke Ferrite (NiFe2O4)

The heat capacity of nickel ferrite was measured as a function of temperature over the range from 50 to 1200 C using a differential scanning calorimeter. A thermal anomaly was observed at 584.9 C, the expected Curie temperature, T{sub c}. The observed behavior was interpreted by recognizing the sum of three contributions: (1) lattice (vibrational), (2) a spin wave (magnetic) component and (3) a {lambda}-transition (antiferromagnetic-paramagnetic transition) at the Curie temperature. The first w… more

Date: December 15, 2005

Creator: S Ziemniak, L Anovitz, R Castelli

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Transient electronic structure of the photoinduced phase of Pr0.7Ca0.3MnO3 probed with soft x-ray pulses

We use time-resolved x-ray absorption near-edge structure spectroscopy to investigate the electronic dynamics associated with the photoinduced insulator-to-metal phase transition in the colossal magnetoresistive manganite Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3}. Absorption changes at the O K and Mn L edges directly monitor the evolution of the density of unoccupied states in the transient photoinduced phase. We show that the electronic structure of the photoinduced phase is remarkably similar to that … more

Date: April 1, 2009

Creator: Rini, M.; Zhu, Y.; Wall, S.; Tobey, R. I.; Ehrke, H.; Garl, T. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

A Magnetocaloric Pump for Lab-On-A-Chip Technology: Phase I Report

A magnetocaloric pump provides a simple means of pumping fluid using only external thermal and magnetic fields. The principle, which can be traced back to the early work of Rosensweig, is straightforward. Magnetic materials tend to lose their magnetization as the temperature approaches the material's Curie point. Exposing a column of magnetic fluid to a uniform magnetic field coincident with a temperature gradient produces a pressure gradient in the magnetic fluid. As the fluid heats up, it los… more

Date: May 8, 2004

Creator: Love, LJL

Item Type: Report

Partner: UNT Libraries Government Documents Department