Xavier Bohigas

Tunable magnetocaloric effect in ceramic perovskites

A large entropy variation (magnetocaloric effect) has been discovered in ceramic perovskites with the formulas La0.65Ca0.35Ti1−xMnxO3−z and La0.5+x+yLi0.5−3yTi1−3xMn3xO3−z. Both Curie temperature and entropy change were studied from 4.2 to 400 K for different stoichiometric compositions and applied magnetic fields. Our conclusion is that these materials are excellent candidates for working materials in magnetic refrigeration and liquefaction devices in a wide temperature range.

Magnetocaloric effect in La0.67Ca0.33MnOδ and La0.60Y0.07Ca0.33MnOδ bulk materials

The dependence of magnetization on the applied magnetic field and temperature was measured carefully near their Curie temperatures for two perovskite manganite samples: La0.67Ca0.33MnOδ and La0.60Y0.07Ca0.33MnOδ. It is suggested by the results that these materials can be utilized as both the thermal storage (passive regeneration) and as the working material (active regeneration) in an active magnetic regenerative refrigerator with very large temperature span, for their significant entropy change upon the application of a magnetic field and the easily tuned Curie temperatures.The dependence of magnetization on the applied magnetic field and temperature was measured carefully near their Curie temperatures for two perovskite manganite samples: La{sub 0.67}Ca{sub 0.33}MnO{sub {delta}} and La{sub 0.60}Y{sub 0.07}Ca{sub 0.33}MnO{sub {delta}}. It is suggested by the results that these materials can be utilized as both the thermal storage (passive regeneration) and as the working material (active regeneration) in an active magnetic regenerative refrigerator with very large temperature span, for their significant entropy change upon the application of a magnetic field and the easily tuned Curie temperatures. {copyright} {ital 1996 American Institute of Physics.}

Giant and time-dependent magnetocaloric effect in high-spin molecular magnets

We have measured and calculated the magnetocaloric effect in macroscopic samples of oriented high-spin molecular clusters like Mn12 and Fe8 as a function of the temperature and both the intensity and the sweeping rate of the applied magnetic field. We have observed a high magnetic entropy variation around the blocking temperature of the magnetic moment of molecules and calculated the shift of the entropy variation and cooling temperature, with the sweeping rate of the magnetic field.

Magnetocaloric effect in random magnetic anisotropy materials

In this letter we report the results of entropy variations in random anisotropy magnets composed of TbxY1−xAl2, with x=0.15, 0.20, 0.25, 0.35, 0.40, and 0.50. We discovered large entropy variation associated with the spin glass to paramagnetic transition. Both temperature transition and entropy changes were studied at different temperatures and with different compositions. Our conclusion is that these materials are suitable candidates for use as magnetic refrigerants in a temperature range below 40 K.

Magnetocaloric effect in La0.65Ca0.35Ti1 − xMnxO3 ceramic perovskites

Abstract In this paper, we comment on experiments we have carried out on ceramic perovskites of composition La 0.65 Ca 0.35 Ti 1 − x Mn x O 3 . From low- and high-field magnetic measurements recorded at different temperatures, we have discovered the existence of a large entropic change associated to the ferrimagnetic—paramagnetic transition. Our conclusion is that these materials are excellent candidates as working materials in refrigeration devices.

Magnetocaloric effect in Mn12 2-Cl benzoate

The magnetocaloric effect in high spin Mn12 2Cl-benzoate clusters was studied. We observed a high entropy change around the blocking temperature of the magnetization. Theoretical simulations indicate the shift of the entropy change with the sweeping rate of the magnetic field.

Semi-virtual lectures on physics

Some years ago, it was believed that the learning process would eventually become mostly virtual. ICT tools were therefore designed with this scenario in mind. Nevertheless, todays learning process is still predominantly face-to-face; at most, we have seen a shift towards blended learning. Today we are in the process of incorporating ICT tools both inside and outside of the classroom. In this paper, we explore how contents—specifically physics contents—can be used optimally either inside or outside of the classroom.

Bubble Detector in Polyurethane Applications Based on a Microwave System

This paper discusses a device that detects bubbles in glue depositions on a windshield glass, which may cause water leakages inside the cockpit. This device is inexpensive, more reliable than other existing solutions, and implements a specific signal treatment and a bubble size calculation model. The device is based on microwave radiation system in the X-band and has been developed and implemented in real production in the final assembly area of the automotive industry

Teaching and Learning Physics Using the Internet: The Baldufa Project

The aim of the Baldufa project that is presented in this article is to help both teachers and students in teaching‐learning activities in physics. A certain amount of HTML documentation is available, at this moment, to be used by students as learning aids. Teachers can propose their own pedagogical strategies via the Internet. For these reasons, the authors have programmed a server and have conceived a teaching package in HTML language.

Comparative study of three audio processors as environments for laboratory activities on wave physics and acoustics

Audio processors allow to implement laboratory activities specially on acoustics. We have evaluated three audio processors (Audacity, WaveLab, and Adobe Audition). Although an overall grade was also calculated as a guideline (not a statement of “the best”), the decision about the most suitable one depends on each particular laboratory activity.