Magnetic anisotropy, first-order-like metamagnetic transitions and large negative magnetoresistance in the single crystal of Gd2_{2}PdSi3_3

Electrical resistivity ($\rho$), magnetoresistance (MR), magnetization, thermopower and Hall effect measurements on the single crystal Gd$_{2}$PdSi$_3$, crystallizing in an AlB$_2$-derived hexagonal structure are reported. The well-defined minimum in $\rho$ at a temperature above N\'eel temperature (T$_N$= 21 K) and large negative MR below $\sim$ 3T$_N$, reported earlier for the polycrystals, are reproducible even in single crystals. Such features are generally uncharacteristic of Gd alloys. In addition, we also found interesting features in other data, e.g., two-step first-order-like metamagnetic transitions for the magnetic field along [0001] direction. The alloy exhibits anisotropy in all these properties, though Gd is a S-state ion.Comment: RevTeX, 5 pages, 6 encapsulated postscript figures; scheduled to be published in Phy. Rev. B (01 November 1999, B1

Residual resistivity ratio and its relation to the positive magnetoresistance behavior in natural multilayer LaMn2Ge2; relevance to artificial multilayer physics

Results of low temperature magnetoresistance ($\Delta\rho/\rho$) and isothermal magnetization (M) measurements on polycrystalline ferromagnetic (T_C close to 300 K) natural multilayers, LaMn_{2+x}Ge_{2-y}Si_y, are reported. It is found that the samples with large residual resistivity ratio, $\rho(300K)/\rho(4.2K)$, exhibit large positive magnetoresistance at high magnetic fields. The Kohler's rule is not obeyed in these alloys. In addition, at 4.5 K, there is a tendency towards linear variation of $\Delta\rho/\rho$ with magnetic field with increasing $\rho(300K)/\rho(4.2K$); however, the field dependence of $\Delta\rho/\rho$ does not track that of M, thereby suggesting that the magnetoresistance originates from non-magnetic layers. It is interesting that these experimental findings on bulk polycrystals are qualitatively similar to what is seen in artificially grown multilayer systems recently.Comment: 5 pages, 3 figures, separate figures. This work is a follow-up of our earlier paper in APL, Ref. : APL Vol 71, pp 2385 (1997

Pion parameters in nuclear medium from chiral perturbation theory and virial expansion

We consider two methods to find the effective parameters of the pion traversing a nuclear medium. One is the first order chiral perturbation theoretic evaluation of the pion pole contribution to the two-point function of the axial-vector current. The other is the exact, first order virial expansion of the pion self-energy. We find that, although the results of chiral perturbation theory are not valid at normal nuclear density, those from the virial expansion may be reliable at such density. The latter predicts both the mass-shift and the in-medium decay width of the pion to be small, of about a few MeV.Comment: 9 Pages RevTex, 3 eps figure

Transport and magnetic anomalies due to A-site ionic size mismatch in La0.5_{0.5}Ca0.5−x_{0.5-x}Ba_{x}MnO3_3

We present results of electrical resistivity, magnetoresistance and ac and dc magnetic susceptibility on polycrystalline samples of the type La(0.5)Ca(0.5-x)Ba(x)MnO(3) synthesized under identical heat treatment conditions. The substitution of larger Ba ions for Ca results in a non- monotonic variation of the curie temperature as the system evolves from a charge ordered insulating state for x=0 to a ferromagnetic metallic state for x=0.5. An intermediate compositino, x=0.1, interestingly exhibits ferromagnetic. insulating behaviour with thermal hysteresis in ac chi around the curie tem- perature (120K). The x=0.2 and 0.3 compounds exhibit semiconducting like behavior as the temperature is lowered below 300K, with a broad peak in rho around 80-100K: These compositions exhibit a weak increase in rho as the temperature lowered below 30K, indicative of electron localization effects. These compositions also undergo ferromagnetic transitions below about 200 and 235K respectively, though these are non-hysteretic; above all, for these compositions, MR is large and conveniently measurable over the entire tempera- ture range of measurement below Tc. This experimental finding may be of interest from the application point of view. We infer that the A-site ionic-size mismatch plays a crucial role in the deciding these properties.Comment: 5 pages, 6 Figures, Resubmitted with extended abstract on 26 Nov, 199

A Content Based Pattern Analysis System for a Biological Specimen Collection

Over the years many research collections of biological specimen have been developed for research in biological sciences. Number of specimens in some of these collections can be as high as several millions. There is a move to convert these physical specimens into digital images. This research is motivated by the need to develop techniques to mine useful information from these large collections of specimen images. Specific focus of this research is on the collection of parasites in the Harold W. Manter Laboratory (HWML) Parasite Collection, one of the top four parasite collections in the world. These parasites closely resemble in shape and have flexible bodies with rigid extremities. They have only a few specific structural differences. In this paper we present a technique to retrieve specimens based on shape of a given sample. This form of mining based on the shape of the specimen has the potential to discover linkages between specimens not otherwise known

Magnetoresistance anomalies and multiple magnetic transitions in SmMn<SUB>2</SUB>Ge<SUB>2</SUB>

The results of magnetoresistance (&#916;&#961;/&#961;), heat capacity (C), and ac susceptibility (&#967;) measurements are reported for a polycrystalline specimen of SmMn2Ge2. In addition to sharp variations of the order of 3-5% at 110 and 142 K, there are anomalies in the sign and the magnitudes of &#916;&#961;/&#961;. A finding of considerable interest is that there is a gradual increase of &#916;&#961;/&#961; from a small negative value at 35 K to a very large value of about 24% at 4.2 K in the presence of a magnetic field of 80 kOe, though apparently there is no corresponding anomaly in the C data. This finding signals the existence of a phase transition below 30 K attributable to magnetic ordering from Sm sublattice, thereby making the origin of the onset of Mn ordering around 110 K a puzzle

Large positive magnetoresistance at low temperatures in a ferromagnetic natural multilayer, LaMn<SUB>2</SUB>Ge<SUB>2</SUB>

The results of magnetoresistance measurements on a naturally occurring multilayer LaMn2Ge2, which is ferromagnetic below 326 K, are reported. The magnitude of magnetoresistance is found to be positive below 70 K gradually increasing to an unusually large value (nearly 100%) at 4.2 K in the presence of a field of 70 kOe as the temperature is lowered, similar to the recent observations by Verbanck, Temst, Mae, Schad, Van Bael, Moshchalkov, and Bruynseraede [Appl. Phys. Lett. 70, 1477 (1997)] in Cr/Ag/Cr trilayers. The positive sign of magnetoresistance for a ferromagnet is unexpected and possible explanations are offered

Advanced characterization and simulation of SONNE: a fast neutron spectrometer for Solar Probe Plus

SONNE, the SOlar NeutroN Experiment proposed for Solar Probe Plus, is designed to measure solar neutrons from 1-20 MeV and solar gammas from 0.5-10 MeV. SONNE is a double scatter instrument that employs imaging to maximize its signal-to-noise ratio by rejecting neutral particles from non-solar directions. Under the assumption of quiescent or episodic small-flare activity, one can constrain the energy content and power dissipation by fast ions in the low corona. Although the spectrum of protons and ions produced by nanoflaring activity is unknown, we estimate the signal in neutrons and γ−rays that would be present within thirty solar radii, constrained by earlier measurements at 1 AU. Laboratory results and simulations will be presented illustrating the instrument sensitivity and resolving power