Alternating Gradient Field Magnetometer Research Articles

Resonant properties of a Flanders alternating gradient field magnetometer: influence of temperature and magnetic moment

The resonant properties of an alternating gradient field magnetometer (AGFM) of the Flanders design have been investigated as a function of temperature and sample magnetic moment. Measurements reveal that room temperature operation of the AGFM is prone to long-term stability problems, which are attributable to variations in ambient temperature, but as long as these variations in temperature are not severe, it is possible to work away from resonance and still reconstruct the m–H loop for a sample. Other variations of the resonant properties of the AGFM, observed when recording m–H loops, have been attributed to the twisting of the AGFM probe when measuring samples with permanent magnetic moments lying in the plane perpendicular to the applied field.

Femtosecond dynamics of Co thin films on Si support

The ultrafast electron and spin dynamics of Co films was investigated using a femto-second pump-probe technique. The samples were magnetically characterized by means of magnetooptical Kerr effect and non-optical magnetometers, i.e. superconductive quantum interference device and alternating gradient field magnetometer. Time evolution of both, Kerr rotation and ellipticity, was measured at different points of the static hysteresis cycle. This allowed separating magnetic and non-magnetic contributions to the signal. The sample magnetization was found to drop within 200 fs, following the pulse cross-correlation trace, while the magnetization recovery time was found to last few picoseconds.

Devitrification-induced variations of magnetic properties of electroplated amorphous film Co76Mo18Ni6

Abstract Thermogravimetric analyzer (TGA) under the influence of a static magnetic field and alternating gradient field magnetometer (AGFM) were applied to study the magnetic properties of electroplated film Co 76 Mo 18 Ni 6 . The film was amorphous before thermal annealing. Data from both magnetic measurements corroborate well with diffraction data. TGA is shown to supply vital information to help resolve the ambiguity in X-ray and electron diffraction data. Furthermore TGA can detect the subtle relaxation of amorphous alloy during a low temperature annealing before 250°C. The relaxation is beyond the detection of current X-ray and electron diffraction technique.

Optical vibrating-sample magnetometer

A highly sensitive method of detecting vibrations of a cantilever in atomic-force microscopy has been introduced as a detector in an alternating-gradient field magnetometer. Use of light is the success of this system as it is compatible with vacuum systems and closed-flux cryostats. The optical signal is electronically conditioned easily. Experimental results show that highly sensitive measurements can be achieved.

Magnetic measurements on HgMnTe epitaxial layers (abstract)

Magnetization measurements have been performed on epitaxial layers of Hg1−xMnxTe (MMT) using an alternating gradient field magnetometer (AGFM). The layers, which have a Mn concentration in the range 0.05<x<0.20, and thicknesses between 1 and 6 μm, are deposited by metalorganic vapor phase epitaxy (MOVPE) techniques. The MMT films are grown on GaAs substrates with CdTe and ZnTe buffer layers. Growth is achieved by the interdiffused multilayer process (IMP), where alternate layers of HgTe and MnTe are deposited, and then heated, to produce diffusion and, hence, Hg1−xMnxTe. The MnTe layers that are grown are roughly 1 nm thick, and so grow in the cubic structure, rather than the nickel arsenide structure observed in the bulk material.1 The magnetization of the majority of the samples is the expected paramagnetic behavior with values of χ close to those observed in the bulk material.2 However, a number of the samples have shown evidence for magnetic order at room temperature, and this is also observed in MnTe layers grown by MOVPE. The samples showing saturation of the magnetization also shown an anomalous behavior of the Hall voltage below 100 K and at fields up to 0.3 T. The anomalies in the HgMnTe samples are thought to be due to MnTe inclusions left over from the MOVPE growth process.