A new magnetic field sensor is presented, based on perpendicular hot electron transport in a giant magnetoresistance (Co/Cu)4 multilayer, which serves as a base region of an n-silicon metal-base transistor structure.A 215% change in collector current is found in 500 Oe (77 K), with typical characteristics of the spin-valve effect. The in-plane magnetoresistance was only 3%. The transistor structure allows the investigation of energy resolved perpendicular transport properties, and in particular spin-dependent scattering of hot electrons in transition-metal as well as rare-earth-based multilayers.PACS numbers: 72. 15. Gd, 73.40.Vz, 75.50.Rr, 85.70.Kh The discovery of giant magnetoresistance in magnetic multilayers [1] (also called the spin-valve effect [2]) has led to a large number of studies on giant magnetoresistance systems. Usually, the resistance of the multilayer is measured with the current in plane (CIP). This is the easiest experimental approach of electrical transport in magnetic multilayers. Devices exhibiting CIP giant magnetoresistance are under development as magnetic field sensors, for instance, in read-back magnetic heads used in magnetic recording technology. However, from a fundamental point of view, the CIP configuration suffers from several drawbacks; the CIP magnetoresistance (MR) is diminished by shunting and channeling [2,3].In particular, uncoupled multilayers or sandwiches with thick spacer layers suffer from this problem, whereas the saturation field in such systems is usually small. Moreover, diffusive surface scattering reduces the MR for sandwiches [2] and thin multilayers [4]. Finally, fundamental parameters of the effect, such as the relative contributions of interface and bulk spin-dependent scatterings, are difficult to obtain using the CIP geometry [5]. Measuring with the current perpendicular to the planes (CPP) solves most of these problems, mainly because the electrons cross all magnetic layers, but a practical difficulty is encountered; the perpendicular resistance of the ultrathin multilayers is too small to be measured by ordinary techniques. The first CPP-MR experiments were reported on Co/Ag multilayers [6], where the multilayer was sandwiched between superconducting Nb leads. In this way, CPP experiments could be performed, albeit only at liquid helium temperatures. The use of microfabrication techniques for CPP measurements from 4.2 to 300 K was first shown for Fe/Cr multilayers [7], where the multilayers were etched into micropillars to obtain a relatively large resistance (a few mA). Both types of measurements have confirmed the larger MR effect for the CPP configuration, but they suffered from the general complexity of realization and measurement techniques. Experiments using electrodeposited nanowires showed CPP-MR up to 15% at RT [8].In this Letter, we present the design, prospects, and experimental results of a new magnetic field sensor and measurement tool based on perpendicular hot electron transport in a spin-valve multilayer: the spin-valve transistor. Here...

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The emission spectrum of Tb3+ substituted in YAG to various concentrations (x in Y3−xTbxAl5O12 ranges from 3×10−5 to 3×10−1) has been measured on samples prepared by two different methods. These methods are powder preparation by coprecipitation and growth of crystalline layers by liquid-phase epitaxy. The spectrum consists of two groups of lines, one group around 550 nm originating from the 5D4 level and one group around 450 nm from the 5D3 level. The intensity of the two groups of lines depends on the method of excitation. In the case of UV excitation (λ=254 nm) the emission intensity for low Tb concentrations is mainly governed by the absorption of the incident radiation. With electron excitation, the energy loss of incoming electrons to ‘‘killer sites’’ in the lattice is found to influence the emission. The ratio, however, of 5D4 to 5D3 intensity is independent of the excitation mode. This ratio tends to a constant value at low concentrations and increases strongly with increasing concentration. These effects are explained by feeding of the 5D3 and 5D4 states from 5d levels, followed by cross relaxation, i.e., 5D3 to 5D4 excitation transfer.

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