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Structural and Magnetic Properties of Dilute Spinel Ferrites
H. Mamiya,N. Terada,H. Kitazawa,A. Hoshikawa,T. Ishigaki 한국자기학회 2011 Journal of Magnetics Vol.16 No.2
Magnetic properties of highly zinc-substituted manganese ferrites are discussed on the basis of cation distribution. High throughput neutron powder diffractometry indicates that the prepared samples possess a nearly normal spinel structure, where the substitution of nonmagnetic zinc ions mainly causes the dilution of magnetic ions in the A-sublattice and consequently affects bond-randomness in the B-sublattice. On the other hand, the estimated occupancy of manganese ions in the B site indicates that random anisotropy effects due to local Jahn-Teller distortions gradually weaken with the substitution. Bulk magnetometry indicates that the substitution smears the transition from a paramagnetic phase to a soft-magnetic phase. Furthermore, at lower temperatures, such a soft-magnetic phase is destabilized and a magnetic glassy state appears. These features of the magnetic properties of dilute spinel ferrites are discussed from the viewpoint of the above-mentioned various types of disorders.
DYNAMICAL MAGNETIC PROPERTIES OF IRON - NITRIDE MAGNETIC FLUIDS
H.Mamiya,I.Nakatani 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.5
Ac susceptibility of iron-nitride magnetic fluids with various particle number densities was measured. The relaxation time increases rapidly as the temperature decreases or the inter-particle interaction increases. The analysis of the data suggests that the activation energy is proportional to (k_BT/Jtyp)^α with α ~-0.24 in the lower temperature range in which the thermal energy is comparable to the magnetic dipole interaction.
Alkam, T.,Mamiya, T.,Kimura, N.,Yoshida, A.,Kihara, D.,Tsunoda, Y.,Aoyama, Y.,Hiramatsu, M.,Kim, H. C.,Nabeshima, T. Springer Science + Business Media 2017 Psychophamacology Vol.234 No.12
<P>Increased risk of attention-deficit/hyperactivity disorder (AD/HD) is partly associated with the early developmental exposure to nicotine in tobacco smoke. Emerging reports link tobacco smoke exposure or prenatal nicotine exposure (PNE) with AD/HD-like behaviors in rodent models. We have previously reported that PNE induces cognitive behavioral deficits in offspring and decreases the contents of dopamine (DA) and its turnover in the prefrontal cortex (PFC) of offspring It is well known that the dysfunction of DAergic system in the brain is one of the core factors in the pathophysiology of AD/HD. Therefore, we examined whether the effects of PNE on the DAergic system underlie the AD/HD-related behavioral changes in mouse offspring. PNE reduced the release of DA in the medial PFC (mPFC) in mouse offspring. PNE reduced the number of tyrosine hydroxylase (TH)-positive varicosities in the mPFC and in the core as well as the shell of nucleus accumbens, but not in the striatum. PNE also induced behavioral deficits in cliff avoidance, object-based attention, and sensorimotor gating in offspring. These behavioral deficits were attenuated by acute treatment with atomoxetine (3 mg/kg, s.c.) or partially attenuated by acute treatment with MPH (1 mg/kg, s.c.). Taken together, our findings support the notion that PNE induces neurobehavioral abnormalities in mouse offspring by disrupting the DAergic system and improve our understanding about the incidence of AD/HD in children whose mothers were exposed to nicotine during their pregnancy.</P>