L. Ghivelder

Magnetic relaxation phenomena and cluster glass properties of La 0.7 − x Y x Ca 0.3 MnO 3 manganites

The dynamic magnetic properties of the distorted perovskite system

Specific heat and magnetic order in LaMnO/sub 3+[delta]/

{\mathrm{La}}_{0.7\ensuremath{-}x}{\mathrm{Y}}_{x}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}

Annealing effects on the magnetic properties of a multifilamentary Cu–Nb composite

(0l~xl~0.15)

Abrupt field-induced transition triggered by magnetocaloric effect in phase-separated manganites

have been investigated by ac susceptibility and dc magnetization measurements, including relaxation and aging studies. All investigated samples display a metal-insulator transition. As yttrium is added in the compounds the overall results show evidence for the gradual appearance of a cluster glass behavior. For the

Magnetization studies of phase separation in La 0.5 Ca 0.5 MnO 3

x=0.15

Nonvolatile magnetoresistive memory in phase separated La0.325Pr0.300Ca0.375MnO3

sample, magnetization measurements as a function of time at various temperatures show that the magnetic relaxation is maximum at a given temperature, well below the ferromagnetic transition. This maximum coincides in temperature with a frequency-dependent feature in the imaginary part of the ac susceptibility, associated with a freezing process. This is interpreted as due to ferromagnetic clusters, which grow with decreasing temperature down to a temperature at which they freeze due to severe intercluster frustration.

Experimental observation of quantum entanglement in low-dimensional spin systems

Magnetic and specific-heat measurements are performed in three different samples of LaMnO_{3+\delta}, with \delta=0.11, 0.15 and 0.26, presenting important disorder effects, such as carrier localization, due to high amounts of La and Mn vacancies. For the samples with \delta =0.11 and 0.15, magnetic measurements show signatures of a two-step transition: as the temperature is lowered, the system enters a ferromagnetic phase followed by a disorder-induced cluster-glass state. Spin-wave-like contributions and an unexpected large linear term are observed in the specific heat as a function of temperature. In the sample with the highest vacancy content, \delta=0.26, the disorder is sufficient to suppress even short-range ferromagnetic order and yield a spin-glass-like state.

Magnetocaloric effect in manganites: Metamagnetic transitions for magnetic refrigeration

Abstract We have studied experimentally the electrical conductivity and specific heat near the superconducting transition of granular samples of YBa 2 Cu 3 O 7− δ , YBa 2 (Cu 2.98 Zn 0.02 )O 7− δ and GdBa 2 Cu 3 O 7− δ . The results show that the transition proceeds in two stages. Careful analysis of the conductivity in the regime of approach to the zero resistance state reveals the occurrence of a coherence transition, which is related to the connective nature of the granular samples. This transition occurs when the fluctuating phases of the order parameter in individual grains become long-range ordered. We obtain the exponent for fluctuation conductivity and the relevant critical temperature, T co , which is close to the point where resistivity vanishes. The specific heat results, when analyzed as d C /d T , show a weak but reproducible cusp-like anomaly at T co . This finding gives strong support to the interpretation of the coherence transition as a genuine critical phenomenon.

Magnetoresistance induced by low-field control of phase separation in La 0.5 Ca 0.5 MnO 3

In this paper, the annealing effects on the magnetic properties of a multifilamentary Cu–15vol%Nb composite were investigated. During vacuum annealing, noticeable changes take place in the microstructure, mostly the partial spheroidization and further coarsening of the niobium filaments. Results show that spheroidization becomes noticeable at about 700 °C and, even after annealing at severe conditions, e.g. 1050 °C for 32 h, the continuity of the niobium-conducting path is partially preserved. The influence of these microstructural changes on the magnetic properties of the multifilamentary Cu–Nb composite conductor is discussed.