23 research outputs found
Anisotropic magnetoresistive and magnetic properties of La_{0.5}Sr_{0.5}CoO_{3-\delta} film
The magnetic and transport properties of La_{0.5}Sr_{0.5}CoO_{3-\delta} film
grown on a LaAlO_3 substrate by pulsed-laser deposition are studied. The
properties are found to be influenced by the magnetic anisotropy and
inhomogeneity. Magnetoresistance anisotropy is determined by the shape
anisotropy of the magnetization and the strain-induced magnetic anisotropy due
to the film-substrate lattice interaction. Indications of the
temperature-driven spin reorientation transition from an out-of plane orderded
state at low temperatures to an in-plane ordered state at high temperatures as
a result of competition between the mentioned sources of magnetic anisotropy
are found.Comment: 5 pages, 8 figures, submitted to Fiz. Nizk. Temp, an extended version
of short communication in cond-mat/020734
Influence of high-energy electron irradiation on the transport properties of La_{1-x}Ca_{x}MnO_{3} films (x \approx 1/3)
The effect of crystal lattice disorder on the conductivity and colossal
magnetoresistance in La_{1-x}Ca_{x}MnO_{3} (x \approx 0.33) films has been
examined. The lattice defects are introduced by irradiating the film with
high-energy (\simeq 6 MeV) electrons with a maximal fluence of about 2\times
10^{17} cm^{-2}. This comparatively low dose of irradiation produces rather
small radiation damage in the films. The number of displacements per atom (dpa)
in the irradiated sample is about 10^{-5}. Nethertheless, this results in an
appreciable increase in the film resistivity. The percentage of resistivity
increase in the ferromagnetic metallic state (below the Curie tempetature
T_{c}) was much greater than that observed in the insulating state (above
T_{c}). At the same time irradiation has much less effect on T_{c} or on the
magnitude of the colossal magnetoresistance. A possible explanation of such
behavior is proposed.Comment: RevTex, 22 pages, 3 Postscript figures, submitted to Eur. Phys. J.
Transport, thermal and magnetic properties of RuSr_2(Gd_{1.5}Ce_{0.5})Cu_2O_{10-\delta}, a magnetic superconductor
Resistivity, thermoelectric power, heat capacity and magnetization for
samples of RuSr_2(Gd_{1.5}Ce_{0.5})Cu_{2}O_{10-\delta} were investigated in the
temperature range 1.8-300 K with a magnetic field up to 8 T. The resistive
transitions to the superconducting state are found to be determined by the
inhomogeneous (granular) structure, characterized by the intragranular, T_{c0},
and intergranular, T_{cg}, transition temperatures. Heat capacity, C(T), shows
a jump at the superconducting transition temperature T_{c0}\approx 37.5 K. A
Schottky-like anomaly is found in C(T) below 20 K. This low temperature anomaly
can be attributed to splitting of the ground term of paramagnetic
Gd^{3+} ions by internal and external magnetic fields.Comment: 3 pages (4 figs. incl.), reported at 50th Magnetism and Magnetic
Materials Conference, San Jose, CA, USA, 200
The upper critical field in superconducting MgB_2
The upper critical field Hc2(T) of sintered pellets of the recently
discovered MgB_2 superconductor was investigated in magnetic fields up to 16 T.
The upper critical field of the major fraction of the investigated sample was
determined from ac susceptibility and resistance data and was found to increase
up to Hc2(0) = 13 T at T = 0 corresponding to a coherence length of 5.0 nm. A
small fraction of the sample exhibits higher upper critical fields which were
measured both resistively and by dc magnetization measurements. The temperature
dependence of the upper critical field, Hc2(T), shows a positive curvature near
Tc and at intermediate temperatures. This positive curvature of Hc2(T) is
similar to that found for the borocarbides YNi_2B_2C and LuNi_2B_2C indicating
that MgB_2 is in the clean limit.Comment: 8 pages with 4 figure
Characteristic crossing point ( K) in specific-heat curves of samples RuSrGdCeCuO taken for different values of magnetic field
Magnetic properties of polycrystalline samples of
RuSr(GdCe)CuO, as-prepared (by
solid-state reaction) and annealed (12 hours at 845C) in pure oxygen
at different pressure (30, 62 and 78 atm) are presented. Specific heat and
magnetization were investigated in the temperature range 1.8--300 K with a
magnetic field up to 8 T. Specific heat, , shows a jump at the
superconducting transition (with onset at K). Below 20 K, a
Schottky-type anomaly becomes apparent in . This low-temperature anomaly
can be attributed to splitting of the ground term of paramagnetic
Gd ions by internal and external magnetic fields. It is found that
curves taken for different values of magnetic field have the same
crossing point (at K) for all samples studied. At the
same time, curves taken for different temperatures have a crossing point
at a characteristic field T. These effects can be
considered as manifestation of the crossing-point phenomenon which is supposed
to be inherent for strongly correlated electron systems.Comment: 10 pages, 7 figures, submitted to J. Phys.: Condens. Matte