Volume 89, Issue 11, 01 June 2001
Index of content:
- GRANULAR AND CPP GMR AND SPIN-VALVE TRANSISTORS
89(2001); http://dx.doi.org/10.1063/1.1357120View Description Hide Description
The dependence of the giant magnetoresistance(GMR) of a metallic granular system on the concentration of magnetic particles is studied numerically. The effect of particle coalescence and dipolar interactions between the particles on the value of optimum GMR and the shape of the concentration dependence curve are discussed. The micromagnetic configuration of the system is obtained by a Monte Carlo algorithm that involves short-range effective exchange couplings and long range dipolar interactions. The conductivity is obtained using Kubo’s formula for a tight binding Hamiltonian. A comparison of our results to experiments on metallic granular films is made.
89(2001); http://dx.doi.org/10.1063/1.1357121View Description Hide Description
Magnetization and magnetoresistance(MR) were studied in as-cast and annealed 450, and 500 °C) samples of melt-spun Field-cooled magnetization curves, when compared with the Curie–Weiss law, suggest the presence of antiferromagnetic interactions between nanoparticles for and 500 °C. Antiferromagnetic interactions have been predicted when dipolar interactions dominate Ruderman–Kittel–Kasuya–Yosida interactions in large particles. Here antiferromagnetic interactions are attributed to particles roughly 4 to 5 nm in size. The largest MR value at and is found for the as-cast material. For samples annealed at 400 °C, MR curves are linear in H above 10 kOe and are in qualitative agreement with a model which considers short-range magnetic scattering by particles of different sizes.
89(2001); http://dx.doi.org/10.1063/1.1361049View Description Hide Description
A new macroscopic ferrimagnet Co–TbN has TbN precipitates in a Co matrix. The Co–TbN system shows the typical magnetic properties of a macroscopic ferrimagnet which are a magnetic compensation point and negative giant magnetoresistance(GMR). The Co–TbN mixture with 32 mole % TbN exhibits 0.72% GMR in fields up to 8 kOe at room temperature and 9% GMR at 250 K in 40 kOe. In the Co–TbN system, the dependence of GMR with temperature is quite different from that of previously studied GMRmaterials that have magnetoresistance decreases with increasing temperature. The GMReffect in the Co–TbN system increases with increasing temperature, because of the increase of ferromagnetic alignment of Co and TbN in a field at higher temperature.
Effect of scattering at lateral edges on the current-perpendicular-to plane giant magnetoresistance of submicronic pillars89(2001); http://dx.doi.org/10.1063/1.1357852View Description Hide Description
From a phenomenological point of view, we have investigated the effect of scattering at lateral edges on the current-perpendicular-to-plane (CPP) transport properties of submicronic magnetic multilayer pillars. This scattering can be considered as a current-in-plane contribution in the CPP geometry. As a first attempt to calculate the CPP resistance and GMR in this situation, we have combined the serial resistance network model of CPP transport with an exponential variation of the local conductivity as a function of the distance from the edges of the pillars assuming that the scattering is perfectly diffusive at the edges of the pillars. As the lateral size of the pillars decreases below 100 nm, it is shown that this scattering leads to a strong increase in the CPP resistivity as well as a decrease in both and area. Furthermore, due to the difference in mean-free paths from layer to layer, the current lines are no longer uniform in the pillar even if the latter is the shape of an infinite cylinder.
89(2001); http://dx.doi.org/10.1063/1.1357853View Description Hide Description
Hot-electron transport in thin films was studied using a spin-valvetransistor. By varying the NiFe thickness from 10 to 100 Å we obtain an attenuation length of 43 Å for majority-spin hot electrons at 0.9 eV above the Fermi level. Based on such relatively long bulk attentuation lengths, one would expect a current transfer ratio that is much larger than the measured value. We propose that the discrepancy can be accounted for by considering interfacial scattering. Increasing the growth quality should thus provide a means to improve the current transfer ratio.