The resistance and magnetoresistance (MR) of three-dimensional current-perpendicular-to-plane (CPP) structures have been calculated via numerical finite element solutions of the Laplace equation. This model accounts for the non-uniform current paths in a four-probe geometry that can yield MR that differs from the intrinsic MR of the isolated CPP pillar with spatially uniform current flow. We calculated the four-probe MR for various geometries and resistivities of both the normal metal leads and the magnetoresistive pillar. From a single, unified approach, we are able to consistently account for the disparate behavior that has been previously published. In particular, we identify conditions that produce four-probe MR that differs from the intrinsic MR of the CPP pillar and highlight those situations where the four-probe resistance is negative. Finally, we present a simple analytical formula for the MR ratio that is applicable to narrow CPP pillars with wide, thin leads.

We describe magnetic field sensors based on a recently discovered magnetoresistance (MR) effect in nonmagnetic organic semiconductor sandwich devices. The MR effect reaches up to 10% in a magnetic field of 10 mT at room temperature. We perform an extensive experimental characterization of this effect. We found that the MR effect is only weakly temperature dependent and does not depend on sign and direction of the applied magnetic field. We also measured the device response to alternating magnetic fields up to 100 kHz. To the best of our knowledge, the discovered MR effect is not adequately described by any of the MR mechanisms known to date.

The goal of this work was to investigate the capabilities of high-power microwaves in manufacture of small-grained barium cerate ceramics. Having compared the samples sintered in the microwave and the thermal fields, we inferred that the microwave sintering occurs at far higher rates. It is also noteworthy that microwave sintering provides a record-breaking low temperature of barium cerate sintering (900°C). Having studied the effect of a microwave field on the microstructure of sintering products, we found that high-power microwave processing significantly reduces the average grain size of barium cerate ceramics.

We discuss properties of an all-optical self-oscillating magnetometer based on an opto-electronic oscillator stabilized with an atomic vapor cell. Proof of the principle DC magnetic field measurements characterized with 2 × 10−7 G sensitivity and 1 − 1000 mG dynamic range in one of the schemes are demonstrated.

Electromagnetic shields and flux concentrators for magnetic sensors could utilize flexible and insulating composites applied using simple thin film deposition methods such as dip-coating, spin-coating, spraying, etc. As the first step towards development of composites with superior performance, efforts focused on isolating nanoparticles with large magnetizations under low fields. In this paper, we provide the results of proof-of-concept studies for two systems: metal-functionalized silicone-based materials (metal-silicone); and, Co-ferrite (Co2+1−xFe2+xFe3+2O4) nanoparticles. The metal-silicone materials studied included a polysiloxane that contained a pendant ferrocene where an optimum saturization magnetization of 5.9 emu/g (coercivity = 11 Oe) was observed. Co-ferrite nanoparticle samples prepared in this study showed unprecendented saturation magnetization (i.e., Ms > 150 emu/g) with low coercivity (Hc ∼ 10 Oe) at room temperature and offer potential application as flux concentrators.

The Hartree-Fock (HF) method is used to synthesize virtually (i.e., fundamental theory-based, computationally) small stable atomic clusters of Ga and In with As and V, and an In-based cluster with As and Mn. The electronic energy level structures (ELSs), optical transition energies (OTEs), and charge/spin density distributions of these clusters have been analyzed. It has been shown that the spin of such clusters is collectivized, and that this collectivization is responsible for a dramatic drop in the clusters’ OTEs as compared to those of similar pyramidal clusters that do not contain “magnetic” atoms.

We are developing a device, the MEMS flux concentrator, that will greatly decrease the effect of 1/f noise in magnetic sensors. It does this by modulating the incoming signal and thus shifting the operating frequency of the sensor. This is accomplished by placing flux concentrators on MEMS structures that oscillate at kHz frequencies. Depending upon the sensor, shifting the operating frequency reduces the 1/f noise by one to three orders of magnitude at one Hz. We have succeeded in fabricating the necessary MEMS structures and observing the desired kHz normal mode resonant frequency. Only microwatts are required to drive the motion. We have used spin valves for our magnetic sensors. The measured field enhancement provided by the flux concentrators agrees to within 3% with the value estimated from finite element calculations. Noise measurements provide strong evidence that the device is likely to reduce the effect of 1/f noise. Flip chip bonding is likely to allow us to fabricate complete, fully functioning sensors.

As an alternative to the magnetoimpedance (MI) devices made from amorphous ribbon or wire, this study proposed a thin film type MI device composed with Ag conductive core and soft ferromagnetic NiFeMo sandwich layers. Obtained optimum sandwich structure was Ta 5 nm/ NiFeMo 300 nm/ Ta 5 nm/ Ag 900 nm/ Ta 5 nm/ NiFeMo 300 nm/ Ta 5 nm, and the width of Ag as 20 µm and the width of NiFeMo as 100 µm. It was patterned by using photolithography and lift-off process. The sandwich structure showed the maximum MI ratio about 40% at the 15 MHz. The impedance change was linear and nearly reversible at the external magnetic field region below the anisotropy field.

Combination of sol-gel technique and microwave treatment is effectively used for the synthesis of neodymium-barium manganite phase with improved microstructure and good magnetic properties.