Jian-Jia Huang

MICROSTRUCTURAL AND MAGNETIC STUDIES OF MN-AL THIN FILMS

Mn–Al thin films with high coercivity and high saturation magnetization were successfully fabricated by rf magnetron sputtering with properly controlled chemical composition, substrate temperature, and annealing temperature. A high coercivity of about 3000 Oe and a saturation magnetization of about 420 emu/cc have been achieved. We have observed that during annealing at 410 °C, the nonmagnetic e phase with a grain size of roughly 100 nm transforms into a metastable ferromagnetic τ phase with a platelike grain size of roughly 300 nm. From the continuous measurement of the stress of the films in vacuum as a function of temperature, we observed a compression stress during heating below 220 °C, and a tension stress above 220 °C during cooling. The structure phase transformation from e to τ phases was related to the stress variation from compression to tension. The high coercivity can be explained by the high magnetocrystalline anisotropy constant of the τ phase and the magnetoelastic energy arises from the residual stress of Mn–Al films after the shear transformation.

Annealing effect on magnetic properties of Si-modified γFe2O3 particles

Abstract Acicular γFe2O3 particles are synthesized by dehydration, reduction and oxidation of acicular γFeOOH particles. The annealing treatment has been added preceding the reduction step in the preparation of acicular γFe2O3 particles. We studied the annealing effect from the investigation of particle morphology, coercive force as well as magnetization. It has been found that Si adsorption on the surface of the particle will significantly improve the annealing effect. Furthermore, it causes an anomalous increase in the coercive force. The origins of annealing effect and Hc enhancement are discussed.

Fabrication and magnetic properties of manganese-aluminium permanent magnets☆

Abstract The magnetic properties of Mn-Al alloys depend on their chemical compositions, grain size, sintering temperature and additives, and are process sensitive. Effects of the sintering temperature, and the carbon addition on the magnetic properties of sintering Mn-Al magnets have been investigated. The electrical resistivity and magnetization of Mn-Al alloys have been studied between 4 and 1200 K. Large differences have been observed between the τ-phase and other non-magnetic phases. The best magnetic properties for the isotropic sintered samples in this study are B r = 2800 G, b H c = 1500 Oe, and ( BH ) max = 1.2 MG Oe.

Neuronal Oscillations in Golgi Cells and Purkinje Cells are Accompanied by Decreases in Shannon Information Entropy

Neuronal oscillations have been shown to contribute to the function of the cerebral cortex by coordinating the neuronal activities of distant cortical regions via a temporal synchronization of neuronal discharge patterns. This can occur regardless whether these regions are linked by cortico-cortical pathways or not. Less is known concerning the role of neuronal oscillations in the cerebellum. Golgi cells and Purkinje cells are both principal cell types in the cerebellum. Purkinje cells are the sole output cells of the cerebellar cortex while Golgi cells contribute to information processing at the input stage of the cerebellar cortex. Both cell types have large cell bodies, as well as dendritic structures, that can generate large currents. The discharge patterns of both these cell types also exhibit oscillations. In view of the massive afferent information conveyed by the mossy fiber–granule cell system to different and distant areas of the cerebellar cortex, it is relevant to inquire the role of cerebellar neuronal oscillations in information processing. In this study, we compared the discharge patterns of Golgi cells and Purkinje cells in conscious rats and in rats anesthetized with urethane. We assessed neuronal oscillations by analyzing the regularity in the timing of individual spikes within a spike train by using autocorrelograms and fast-Fourier transform. We measured the differences in neuronal oscillations and the amount of information content in a spike train (defined by Shannon entropy processed per unit time) in rats under anesthesia and in conscious, awake rats. Our findings indicated that anesthesia caused more prominent neuronal oscillations in both Golgi cells and Purkinje cells accompanied by decreases in Shannon information entropy in their spike trains.

Plasticity of cerebellar Purkinje cells in behavioral training of body balance control.

Neural responses to sensory inputs caused by self-generated movements (reafference) and external passive stimulation (exafference) differ in various brain regions. The ability to differentiate such sensory information can lead to movement execution with better accuracy. However, how sensory responses are adjusted in regard to this distinguishability during motor learning is still poorly understood. The cerebellum has been hypothesized to analyze the functional significance of sensory information during motor learning, and is thought to be a key region of reafference computation in the vestibular system. In this study, we investigated Purkinje cell (PC) spike trains as cerebellar cortical output when rats learned to balance on a suspended dowel. Rats progressively reduced the amplitude of body swing and made fewer foot slips during a 5-min balancing task. Both PC simple (SSs; 17 of 26) and complex spikes (CSs; 7 of 12) were found to code initially on the angle of the heads with respect to a fixed reference. Using periods with comparable degrees of movement, we found that such SS coding of information in most PCs (10 of 17) decreased rapidly during balance learning. In response to unexpected perturbations and under anesthesia, SS coding capability of these PCs recovered. By plotting SS and CS firing frequencies over 15-s time windows in double-logarithmic plots, a negative correlation between SS and CS was found in awake, but not anesthetized, rats. PCs with prominent SS coding attenuation during motor learning showed weaker SS-CS correlation. Hence, we demonstrate that neural plasticity for filtering out sensory reafference from active motion occurs in the cerebellar cortex in rats during balance learning. SS-CS interaction may contribute to this rapid plasticity as a form of receptive field plasticity in the cerebellar cortex between two receptive maps of sensory inputs from the external world and of efference copies from the will center for volitional movements.

Magnetic properties and microstructure of lanthanum-doped Mn-Al and Mn-Al-C permanent magnets

Abstract(Mn0.54Al0.46) 100−xLax and (Mn0.535Al0.448C0.017) 100−xLax alloys, with x up to 0.9, were synthesized and examined by powder X-ray diffraction and magnetic measurements. Lattice parameters, Curie temperature, Tc, coercivity, iHc, and saturation magnetization, Ms, were determined. Phase analysis revealed that Al8LaMn4 precipitates were produced due to the lanthanum addition. A slight increase in the iHc was observed for x ≤ 0.3 in the cast MnAlLa alloys. No significant changes in lattice parameters and Tc were observed for these lanthanum-doped alloys. For sintered isotropic magnets, which were prepared by conventional powder metallurgy processes, the iHc was enhanced on doping with lanthanum. The (BH)max values were also increased. The increment of (BH)max was about 16% for x = 0.3. Higher lanthanum intensity at grain boundaries was observed on examination of the energy-dispersive X-ray spectra (EDX). The reasons for the increase in iHc may be due to the fine precipitates of lanthanum in the grain boundaries.

MAGNETIC PROPERTIES AND MICROSTRUCTURE OF MN-AL-C THIN FILMS

MnxAl100−x−yCy thin films with x=35–65 at. % and y=0–2.4 at. % were prepared by rf magnetron sputtering. Effects of the chemical composition and annealing temperature on the magnetic properties and microstructure of Mn–Al–C films were investigated. X-ray analysis shows that the as-deposited Mn–Al–C thin films are amorphous, and their saturation magnetization is very low. After annealing at temperatures between 400 and 550 °C in vacuum for 30 min, the magnetic phase with higher carbon concentration shows better thermal stability. The best annealing condition was found to be at 410 °C for 30 min. A ferromagnetic τ phase with a grain size of roughly 200–250 nm appeared at a composition range between 40 and 60 at. % Mn for MnxAl99−xC1 thin films; and the sample with Mn50Al49C1 has high coercivity and moderate saturation magnetization. The carbon addition can increase the thermal stability of the coercivity of the Mn–Al thin films.

Preparation and magnetical studies of Mn50Al50/Al bilayer films

Mn50Al50/Al bilayer films were fabricated on a glass substrate by rf magnetron sputtering. The films were subsequently heat-treated in order to transform nonmagnetic MnAl e-phase to magnetic τ-phase. The addition of Al buffer layer could enhance the adhesion of the MnAl films, and for Mn50Al50/Al bilayer films with Al layer thickness between 5 and 15 nm, we can obtain high saturation magnetization (>390 emu/cm3), and high coercivity (>2200 Oe) Mn50Al50/Al films for practical usage. Bending beam method analysis shows that the larger the residual stress of the Mn50Al50/Al bilayer film is, the higher the coercivity is. The relations between the saturation magnetization, the coercivity and the phase transition, the microstructures of the films are discussed.

Collateral projections from vestibular nuclear and inferior olivary neurons to lobules I/II and IX/X of the rat cerebellar vermis: a double retrograde labeling study

Axon collateral projections to various lobules of the cerebellar cortex are thought to contribute to the coordination of neuronal activities among different parts of the cerebellum. Even though lobules I/II and IX/X of the cerebellar vermis are located at the opposite poles in the anterior–posterior axis, they have been shown to receive dense vestibular mossy fiber projections. For climbing fibers, there is also a mirror‐image‐like organisation in their axonal collaterals between the anterior and posterior cerebellar cortex. However, the detailed organisation of mossy and climbing fiber collateral afferents to lobules I/II and IX/X is still unclear. Here, we carried out a double‐labeling study with two retrograde tracers (FluoroGold and MicroRuby) in lobules I/II and IX/X. We examined labeled cells in the vestibular nuclei and inferior olive. We found a low percentage of double‐labeled neurons in the vestibular nuclei (2.1 ± 0.9% of tracer‐labeled neurons in this brain region), and a higher percentage of double‐labeled neurons in the inferior olive (6.5 ± 1.9%), especially in its four small nuclei (18.5 ± 8.0%; including the β nucleus, dorsal cap of Kooy, ventrolateral outgrowth, and dorsomedial cell column), which are relevant for vestibular function. These results provide strong anatomical evidence for coordinated information processing in lobules I/II and IX/X for vestibular control.

Granger causality-based synaptic weights estimation for analyzing neuronal networks

Granger causality (GC) analysis has emerged as a powerful analytical method for estimating the causal relationship among various types of neural activity data. However, two problems remain not very clear and further researches are needed: (1) The GC measure is designed to be nonnegative in its original form, lacking of the trait for differentiating the effects of excitations and inhibitions between neurons. (2) How is the estimated causality related to the underlying synaptic weights? Based on the GC, we propose a computational algorithm under a best linear predictor assumption for analyzing neuronal networks by estimating the synaptic weights among them. Under this assumption, the GC analysis can be extended to measure both excitatory and inhibitory effects between neurons. The method was examined by three sorts of simulated networks: those with linear, almost linear, and nonlinear network structures. The method was also illustrated to analyze real spike train data from the anterior cingulate cortex (ACC) and the striatum (STR). The results showed, under the quinpirole administration, the significant existence of excitatory effects inside the ACC, excitatory effects from the ACC to the STR, and inhibitory effects inside the STR.