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Alex de Lozanne

Publications and source records attributed to Alex de Lozanne.

6 recordsLinked to original sources
PubMed2006

Magnetic imaging of a supercooling glass transition in a weakly disordered ferromagnet.

Spin glasses are founded in the frustration and randomness of microscopic magnetic interactions. They are non-ergodic systems where replica symmetry is broken. Although magnetic glassy behaviour has been observed in many colossal magnetoresistive manganites, there is no consensus that they are spin glasses. Here, an intriguing glass transition in (La,Pr,Ca)MnO3 is imaged using a variable-temperature magnetic force microscope. In contrast to the speculated spin-glass picture, our results show that the observed static magnetic configuration seen below the glass-transition temperature arises from the cooperative freezing of the first-order antiferromagnetic (charge ordered) to ferromagnetic transition. Our data also suggest that accommodation strain is important in the kinetics of the phase transition. This cooperative freezing idea has been applied to structural glasses including window glasses and supercooled liquids, and may be applicable across many systems to any first-order phase transition occurring on a complex free-energy landscape.

Journal Article↗
PubMed2006

Application of magnetic force microscopy in nanomaterials characterization.

This review describes the basic technical aspects of magnetic force microscopy and how this technique has been applied to the study of colossal magnetoresistance materials, superconductors, and patterned magnetic materials. Recently, current distribution in a patterned aluminum strip has been measured by magnetic force microscopy, opening the possibility of measuring currents in buried interconnects in integrated circuits.

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PubMed2003

Wavy and rough cracks in silicon.

Single-crystal silicon exhibits a strong preference to cleave along a few certain planes, but in experiments we observe wavy cracks with almost no evidence of a preferred fracture direction. Furthermore, we find that the fracture surface is an anisotropic and self-affine fractal over five decades in length scale in the direction of the crack with a roughness exponent of 0.78. In our experiments a 1-4 cm wide strip of single-crystal silicon is heated to 378 degrees C and lowered into a 20 degrees C water bath at speeds of 0.2-5 cm/s. The thermal gradient produces cracks that, depending on the speed, are straight, wavy with amplitude 0.1-0.5 cm and wavelength 0.3-1 cm, or multibranched. The transition from one mode of fracture to another is discontinuous and hysteretic.

Journal Article↗
PubMed2002

Direct observation of percolation in a manganite thin film.

Upon cooling, the isolated ferromagnetic domains in thin films of La0.33Pr0.34Ca0.33MnO3 start to grow and merge at the metal-insulator transition temperature TP1, leading to a steep drop in resistivity, and continue to grow far below TP1. In contrast, upon warming, the ferromagnetic domain size remains unchanged until near the transition temperature. The jump in the resistivity results from the decrease in the average magnetization. The ferromagnetic domains almost disappear at a temperature TP2 higher than TP1, showing a local magnetic hysteresis in agreement with the resistivity hysteresis. Even well above TP2, some ferromagnetic domains with higher transition temperatures are observed, indicating magnetic inhomogeneity. These results may shed more light on the origin of the magnetoresistance in these materials.

Journal Article↗