arXiv subjects

P. Svedlindh

Publications and source records attributed to P. Svedlindh.

25 records · Page 2Linked to original sources

arXiv2001

Magnetotransport in a bi-crystal film of La_0.7Sr_0.3MnO_3

Transport properties of an epitaxial film of La_0.7Sr_0.3MnO_3 (LSMO), deposited epitaxially on a LaAlO_3 bi-crystal substrate having a misorientation angle of 9.2 deg., have been studied. The film was patterned into a meander containing 100 grain boundaries. The resistivity of the sample exhibits two components; one originating from the grain boundary regions, and one from the LSMO elements in the meander; the latter contribution is similar to the resistivity of a reference epitaxial LSMO film. The low (<0.5 T) and high (up to 6 T) field magnetoresistance was also studied. The meander show a large low field magnetoresistance, increasing with decreasing temperature, and a constant high field slope of the magnetoconductance, results that are well explained by a two-step spin polarized tunneling model.

cond-mat.mtrl-sci↗

arXiv2001

Fragility of the spin-glass-like collective state to a magnetic field in an interacting Fe-C nanoparticle system

The effect of applied magnetic fields on the collective nonequilibrium dynamics of a strongly interacting Fe-C nanoparticle system has been investigated. It is experimentally shown that the magnetic aging diminishes to finally disappear for fields of moderate strength. The field needed to remove the observable aging behavior increases with decreasing temperature. The same qualitative behavior is observed in an amorphous metallic spin glass (Fe_{0.15}Ni_{0.85})_{75}P_{16}B_6Al_3.

cond-mat.mtrl-sci↗

arXiv2001

Structural and magnetic properties of GaMnAs layers with high Mn content grown by Migration Enhanced Epitaxy on GaAs(100) substrates

We have grown the ferromagnetic semiconductor GaMnAs containing up to 10% Mn by migration enhanced epitaxy at a substrate temperature of 150^oC. The alternate supply of As2 molecules and Ga and Mn atoms made it possible to grow single crystalline GaMnAs layers at very low substrate temperature, at which conventional molecular beam epitaxial growth under excess As supply is not possible due to As condensation. Secondary ion mass spectroscopy and X-ray diffraction measurements confirmed a higher Mn content in the films grown by this method in comparison to the GaMnAs layers grown by low temperature molecular beam epitaxy. The lattice constant of hypothetical zinc-blende structure MnAs is determined to be 5.9 Å, which deviates somewhat from previously reported values. This deviation is ascribed to growth-condition dependent density of point defects. It is stressed that this effect must be taken into account for any assessment of Mn content from X-ray diffraction data. Magnetization measurements showed an onset of ferromagnetic ordering around 75 K for the GaMnAs layer with 10% Mn. This means that the trend of falling Curie temperatures with increasing Mn concentrations above 5.5% is broken. We tentatively assign this to the variation of the carrier concentration, including contributions from donor and acceptor centers formed by antisite defects and Mn doping, and increased density of magnetically active Mn ions.

cond-mat.mtrl-sci↗

arXiv2000

Spin glass like transition in a highly concentrated Fe-C nanoparticle system

A highly concentrated (17 vol.%) Fe-C nano-particle system, with a narrow size distribution $d = 5.4\pm 0.4$ nm, has been investigated using magnetic ac susceptibility measurements covering a wide range of frequencies (17 mHz - 170 Hz). A dynamic scaling analysis gives evidence for a phase transition to a low temperature spin-glass-like phase. The critical exponents associated with the transition are $zν= 10.5 \pm 2$ and $β= 1.1 \pm 0.2$. The reason why the scaling analysis works for this sample, while it may not work for other samples exhibiting collective behavior as evidenced by aging phenomena, is that the single particle contribution to $χ''$ is vanishingly small for $T>T_g$ and hence all slow dynamics is due to collective behavior. This criterion can only be fulfilled for a highly concentrated nano-particle sample with a narrow size distribution.

cond-mat.mtrl-sci↗

arXiv2000

Grain boundary effects on magnetotransport in bi-epitaxial films of La$_{0.7}$Sr$_{0.3}$MnO$_3$

The low field magnetotransport of La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) films grown on SrTiO$_3$ substrates has been investigated. A high qualtity LSMO film exhibits anisotropic magnetoresistance (AMR) and a peak in the magnetoresistance close to the Curie temperature of LSMO. Bi-epitaxial films prepared using a seed layer of MgO and a buffer layer of CeO$_2$ display a resistance dominated by grain boundaries. One film was prepared with seed and buffer layers intact, while a second sample was prepared as a 2D square array of grain boundaries. These films exhibit i) a low temperature tail in the low field magnetoresistance; ii) a magnetoconductance with a constant high field slope; and iii) a comparably large AMR effect. A model based on a two-step tunneling process, including spin-flip tunneling, is discussed and shown to be consistent with the experimental findings of the bi-epitaxial films.

cond-mat.mtrl-sci↗

arXiv2000

Reentrant spin glass transition in La$_{0.96-y}$Nd$_{y}$K$_{0.04}$MnO$_3$: origin and effects on the colossal magnetoresistivity

Magnetic, electric and structural properties of La$_{0.96-y}$Nd$_y$K$_{0.04}$MnO$_{3+δ}$ with 0$\leq y \leq$0.4 have been studied experimentally. A disordered magnetic state is formed as La is substituted by Nd, reflecting the competition between ferromagnetic (FM) double exchange and antiferromagnetic superexchange interactions. Key structural parameters are identified and correlated with changes in magnetic and electric properties. By application of a large magnetic field, spin disorder scattering is removed, creating a new magnetoresistance peak at a temperature lower than the first near-$T_c$ peak. Time dependent zero-field-cooled magnetisation measurements have been performed for $y$=0.4 around this temperature. A reentrant spin glass (RSG) transition is evidenced, with low field ageing properties in both the RSG and FM phases, similar to those observed in archetypal spin glass materials.

cond-mat.mtrl-sci↗

arXiv1999

Nonlinear dynamic susceptibilities of interacting and noninteracting nanoparticle systems

The linear and cubic dynamic susceptibilities of solid dispersions of nano-sized maghemite particles have been measured for three samples with a volume concentration of magnetic particles ranging from 0.3 % to 17 %, in order to study the effect of dipole-dipole interactions. Significant differences between the dynamic response of the three samples are observed. The dynamic susceptibilities of the most dilute sample compare reasonably well with an existing theory for the linear and cubic dynamic susceptibilities of an assembly of noninteracting, uniaxial magnetic particles. The nonlinear dynamic response of the most concentrated sample exhibits at low temperatures some of the features observed in a Ag(11 at.% Mn) spin glass.

cond-mat.mtrl-sci↗