A.L. Brandl

Blocking phenomena in granular magnetic alloys through magnetization, Hall effect, and magnetoresistance experiments

Magnetization and magnetotransport were measured in CoxAg1−x granular composites as a function of temperature and applied magnetic field. A transition from blocked to superparamagnetic behavior with increasing temperatures can be observed in magnetization, giant magnetoresistance and the extraordinary Hall effect measurements. However, the blocking temperature determined from magnetotransport measurements is systematically lower than the one estimated from magnetic measurements. This is due to the selective magnetic scattering, which is enhanced for smaller particles, while the magnetization probes the whole particle size distribution.

Cluster glass-like behavior in a 2D bimetallic molecule-based magnet

The compound of formula Na2[Co2{Cu(opba)}3]/2DMSO/6H2O has been synthesized where opba stands for ortho phenylenebis(oxamato) and DMSO is dimethylsulfoxide. Magnetic properties have been investigated in the 2/300 K temperature range. The compound presents a large coercive field, around 3.5 kOe at 4.2 K, and the A.C. susceptibility measurements has revealed a cluster glass-like behavior. # 2003 Elsevier Science Ltd. All rights reserved.

Magnetotransport, magnetic, and structural properties of TM–SiO2 (TM=Fe, Co, Ni) granular alloys

TM{sub x}(SiO{sub 2}){sub 1-x} (transition metals, or TM=Fe, Co, Ni) thin films were prepared in a wide concentration range with the purpose of studying the giant Hall effect (GHE). The structure was studied using transmission electron microscopy (TEM), X-ray diffraction (XRD), and small angle X-ray scattering (SAXS). Magnetic, transport, and magnetotransport properties were investigated by means of magnetization, resistivity, and Hall effect measurements. TEM images show nanometer-sized spherical structures embedded in an SiO{sub 2} amorphous matrix, with typical sizes ranging from 2 to 7 nm when TM volume concentration x is increased. SAXS measurements show a broadened peak. XRD measurements show that the system consists of amorphous SiO{sub 2} and a crystalline peak, corresponding to small TM crystallites. The observed magnetic properties are strongly dependent on x, and clearly display an evolution resulting from the progressive increase in the mean particle size. Above the percolation threshold region all samples display GHE. Relationships between structure and magnetotransport properties are discussed.

Study of interactions in Co–SiO2 granular films by means of MFM and magnetization measurements

A study of Co[SiO2] granular films using magnetic force microscopy (MFM), transmission electron microscopy and DC magnetization is presented. MFM shows large strip magnetic domains in the percolated system and allows a more direct investigation of the magnetic interaction among grains in the film with the lowest metal volume fraction.

Magnetic properties of the solid electrolytes: Li3Fe2(MO4)3 (M=P, As)

Abstract Magnetization measurements DC/AC show that the title compounds order antiferromagnetically at 29 and 36 K for P and As, respectively. Below this temperature a weak ferromagnetic component arises, which diminishes with temperature. These results are explained by the competition between two different magnetic sublattices, corresponding to the Fe(1) and Fe(2) sites. The observed weak ferromagnetic component is explained by an incomplete compensation of the collinear arrangement of the moments (weak ferrimagnetism) for the M=P sample and by slight canting of the magnetic moments in the ordered state (weak ferromagnetism) for the M=As sample.