Peter Svedlindh | Uppsala University (original) (raw)

Papers by Peter Svedlindh

Thin Solid Films, 2002

We have studied the magnetic properties of (GaMnAs) m (GaAs) n superlattices with magnetic GaMnAs... more We have studied the magnetic properties of (GaMnAs) m (GaAs) n superlattices with magnetic GaMnAs layers of thickness between 8 and 16 molecular layers (ML) (23Ð45 •), and with nonmagnetic GaAs spacers from 4 ML to 10 ML (11Ð28 •).

Journal of Magnetism and Magnetic Materials, 2001

Room temperature x-ray diffraction, magnetization and neutron diffraction measurements up to 500 ... more Room temperature x-ray diffraction, magnetization and neutron diffraction measurements up to 500 K have been carried out on polycrystalline bulk double perovskites AA FeMoO 6 (AA = Ba 2 , BaSr, Sr 2 , Ca 2 ) in order to determine and correlate their structural and magnetic properties. As the average ionic radius is diminished, the crystallographic structure evolves from cubic (for AA = Ba 2 , BaSr) to tetragonal (Sr 2 ) and finally to monoclinic (Ca 2 ). In the case of AA = Sr 2 , a novel crossover from a high temperature paramagnetic cubic state to a low temperature ferrimagnetic tetragonal state has been observed. For all the studied compounds, neutron diffraction patterns and magnetization measurements are consistent with a ferrimagnetic ordering of the Fe and Mo sublattices. A remarkable correlation is found between the Curie temperature and the electronic bandwidth, which is controlled by structural parameters. §

Journal of Alloys and Compounds, 2004

Nanoferrites of composition Mn 1−x Ni x Fe 2 O 4 with x = 0.00, 0.25, 0.50, 0.75, 1.00 were prepa... more Nanoferrites of composition Mn 1−x Ni x Fe 2 O 4 with x = 0.00, 0.25, 0.50, 0.75, 1.00 were prepared by the chemical coprecipitation method. The prepared nanoferrites were characterized by infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) and vibrating sample magnetometer (VSM) to study the compositional, structural, morphological and magnetic changes taking place with varying Ni concentration in the composition of the prepared nanoferrites. IR reveals the presence of both highfrequency and low-frequency bands due to tetrahedral and octahedral sites, respectively. The XRD results indicated the formation of single spinel ferrite with crystalline size in the range of 14-26 nm. The lattice parameters (a) decrease with the increase of the Ni concentration x in the lattice. Further information about the morphology of the nanoferrites was obtained from the AFM and SEM results. The magnetic hysteresis curves clearly indicate the soft nature of the prepared nanoferrites. Various magnetic properties such as saturation magnetization (M s ) and remanence (M r ) are calculated from the hysteresis loops and observed to be dependent on the composition. A. Faraz · N.M. Ahmad ( ) · Fazal-ur-Rehman · A. Maqsood ·

Physical Review Letters, 2002

We show that magnetic structures involving partial disorder of local magnetic moments on the Mn a... more We show that magnetic structures involving partial disorder of local magnetic moments on the Mn atoms in (Ga(1)-(x)Mn(x))As lower the total energy, compared to the case of perfect ferromagnetic ordering, when As defects on the Ga sublattice are present. Such magnetic structures are found to be stable for a range of concentrations of As antisites, and this result accounts for the observed magnetic moments and critical temperatures in (Ga(1)-(x)Mn(x))As. We propose an explanation for the stabilization of the partially disordered magnetic structures and conclude that the magnetization and critical temperatures should increase substantially by reducing the number of As antisite defects.

Physical Review Letters, 1998

The field dependence of the ac susceptibility of a concentrated frozen ferrofluid containing ultr... more The field dependence of the ac susceptibility of a concentrated frozen ferrofluid containing ultrafine Fe-C particles of monodisperse nature has been analyzed using static scaling. For the first time, a divergent behavior of the nonlinear susceptibility of a dipole-dipole interacting system is demonstrated. From the analysis, the critical exponents g 4.0 6 0.2 and b 1.2 6 0.1 were extracted. The results support the existence of a low temperature spin-glass-like phase in interacting magnetic nanoparticle systems. [S0031-9007(98)07527-9]

Physica C-superconductivity and Its Applications, 1988

The relaxation of the magnetization of a sintered sample of YBa2Cu3O7 has been investigated in a ... more The relaxation of the magnetization of a sintered sample of YBa2Cu3O7 has been investigated in a SQUID-magnetometer. The relaxation may adequately be described by a power law t-a at all fields (1-100 gauss) and temperatures (20-90 K) investigated. A marked field dependence of the exponent a and a corresponding field dependence in the relaxation rate (1/H ∂M/∂ln t) is observed.

Physical Review Letters, 1988

The dynamics of the short-range Ising spin-glass Fe0.5Mn0.5TiO3 has been investigated in a SQUID ... more The dynamics of the short-range Ising spin-glass Fe0.5Mn0.5TiO3 has been investigated in a SQUID magnetometer. The dynamic spin-correlation function, q(t), as reflected in low-field ac susceptibility and time-dependent magnetization measurements, was studied in the time interval 10-6-104 sec. The functional form of q(t) shows a remarkable agreement with the results obtained from Monte Carlo simulations on a three-dimensional Ising spin-glass.

Physical Review B, 1992

The crossover between quasiequilibrium and nonequilibrium spin-glass dynamics has been studied in... more The crossover between quasiequilibrium and nonequilibrium spin-glass dynamics has been studied in Monte Carlo simulations of two-and three-dimensional short-range Ising spin-glass systems. The spin system was quenched in zero field to a low temperature T. After ...

Physical Review B, 1995

Experimental results of the temperature, field, and time dependence of the magnetization in high-... more Experimental results of the temperature, field, and time dependence of the magnetization in high-temperature superconductors displaying the paramagnetic Meissner effect are compared with numerical results from model calculations. In experiments the relaxation rate of the zero-field-cooled magnetization exhibits novel field-dependent properties and the field-cooled magnetization is found to increase with time. A model based on an ensemble of superconducting loops,

Physica C-superconductivity and Its Applications, 1989

The low field susceptibility of a sintered sample of Bi2Sr2Ca1Cu2O8+delta has been investigated i... more The low field susceptibility of a sintered sample of Bi2Sr2Ca1Cu2O8+delta has been investigated in a SQUID magnetometer. In the low field FC susceptibility a new feature of high-Tc superconductors is revealed, an antimeissner effect. Vortex pair fluctuations and pinning are believed to be essential for the observed behaviour.

Physical Review Letters, 1997

The dynamics of a magnetic particle system consisting of ultrafine Fe-C particles of monodisperse... more The dynamics of a magnetic particle system consisting of ultrafine Fe-C particles of monodisperse nature has been investigated in a large time window, 10 29 10 4 s, using Mössbauer spectroscopy, ac susceptibility, and zero field cooled magnetic relaxation measurements. By studying two samples from the same dilution series, with concentrations of 5 and 6 3 10 23 vol %, respectively, it has been found that dipole-dipole interaction increases the characteristic relaxation time of the particle system at all temperatures investigated. The results for the most concentrated particle assembly are indicative of collective magnetic dynamics and critical slowing down at a finite temperature, T g ഠ 40 K. Close to and below the transition temperature, an aging phenomenon is observed, another manifestation of collective magnetic dynamics. [S0031-9007(97)

Physical Review B, 1982

Long-time (5-104 sec) superconducting-quantum-interference-device magnetometry measurements on a ... more Long-time (5-104 sec) superconducting-quantum-interference-device magnetometry measurements on a Au-8 at.% Fe spin-glass imply the existence of a well-defined characteristic time, beyond which no additional change of magnitude or position of the susceptibility cusp occurs. This characteristic time is 5 × 102 sec at an applied field of 0.1 mT (1 G) and estimated to be 105 sec at zero field.

Physical Review B, 1987

The low-field time-dependent magnetic susceptibility of the amorphous metallic spin glass (Fe0.15... more The low-field time-dependent magnetic susceptibility of the amorphous metallic spin glass (Fe0.15Ni0.85) 75P16B6A13 has been studied in a superconducting-quantum-interference-device magnetometer. Both ac susceptibility and zero-field-cooled susceptibility measurements have been utilized to cover more than ten decades in time, 3×10-6-105 sec. At short observation times the equilibrium relaxation is observed, while at long observation times the influence of the aging process

Physical Review B, 1986

The functional form of the relaxation of the thermoremnant magnetization of CuMn spin glass has b... more The functional form of the relaxation of the thermoremnant magnetization of CuMn spin glass has been investigated. A remarkable influence of the aging process of the spin-glass state, which can give an apparent stretched exponential form of the total relaxation, is demonstrated. The spin-glass relaxation can be described by a nearly logarithmic function superimposed by an additional relaxation due to

Physical Review Letters, 1983

SQUID magnetometry measurements on a Cu Mn spin-glass reveal that the zero-field-cooled magnetiza... more SQUID magnetometry measurements on a Cu Mn spin-glass reveal that the zero-field-cooled magnetization strongly depends on the time the sample is kept at constant temperature prior to the field application. This result is evidently at variance with the common belief that an equilibrium spin-glass state is quickly obtained after cooling in zero field. The nonequilibrium behavior, as reflected in the complex time dependence of ∂m∂lnt, is interpreted to arise from slow dynamics of the relaxation-time spectrum.

Physical Review B, 1997

... time effect is clearly observed, showing that the autocorrelation function q(t;tw ) represent... more ... time effect is clearly observed, showing that the autocorrelation function q(t;tw ) represents an alternative for investigating the ageing ... 3 for the monodispersive system. ... It is found that collective behavior to a large extent governs the dynamics at low temperatures in a concentrated ...

Journal of Magnetism and Magnetic Materials, 1995

AC susceptibility and magnetic relaxation experiments have been performed on frozen ferrofluids c... more AC susceptibility and magnetic relaxation experiments have been performed on frozen ferrofluids con&i domain particles of Fe,O,. Interaction effects are identified by comparing results from different partick concert For a system containing uniaxial single domain particles with volume V, and anisotropy energy K, the energy in zero magnetic field can be written as [l j E, = -~Kv,si&~, (i)

Physical Review B, 1998

The effects of a dipole-dipole interaction on the magnetic relaxation in a magnetic nanoparticle ... more The effects of a dipole-dipole interaction on the magnetic relaxation in a magnetic nanoparticle system have been investigated using ac-susceptibility, magnetic relaxation, and magnetic noise measurements, which altogether cover a time window of nine decades. In the experimental time window, it is possible to distinguish two temperature regimes: a low-temperature regime where collective dynamics is probed, as evidenced by the

Physical Review Letters, 1995

The influence of dipolar interaction in a frozen ferrofluid has been experimentally studied. The ... more The influence of dipolar interaction in a frozen ferrofluid has been experimentally studied. The ferrofluid consisted of particles of gamma-Fe2O3 with mean diameter 70 Å. Four samples with volume concentration of magnetic particles ranging from 0.03% to 17% have been investigated. The magnetic relaxation of the most concentrated particle system shows typical spin glass dynamics at low temperature, e.g., the

Cryogenics, 1992

Thin films of YBa2Cu307 (YBCO) were deposited on single crystalline LaAIO 3 substrates using d.c.... more Thin films of YBa2Cu307 (YBCO) were deposited on single crystalline LaAIO 3 substrates using d.c. magnetron sputtering. The quality of the films has been assessed by X-ray diffraction; YBa2Cu307 grows epitaxially with the c-axis parallel to the substrate normal. For some choices of the deposition parameters in the sputtering process, it was found that secondary phases were precipitated in the films. By a deliberate choice of deposition parameters, semi-coherently grown Y203 (yttria) inclusions could be obtained. They had square platelet or cubical shapes with sizes from 5-20 nm and thickness -10 nm. The superconducting properties of the YBa2Cu307 films were investigated using SQUID magnetometry. Magnetization measurements on films with different densities of semicoherent Y203 inclusions indicate an enhanced flux pinning capability with increasing inclusion density.