Electron Paramagnetic Resonance Study of a Langmuir-Blodgett Film of Manganese Octadecylphosphonate and Comparison of the Magnetic Properties to Those of Solid-State Manganese Alkylphosphonates

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• 作者：Candace T. Seip ; Houston Byrd ; and Daniel R. Talham
• 刊名：Inorganic Chemistry
• 出版年：1996
• 出版时间：June 5, 1996
• 年：1996
• 卷：35
• 期：12
• 页码：3479 - 3483
• 全文大小：198K
• 年卷期：v.35,no.12(June 5, 1996)
• ISSN：1520-510X

文摘

Langmuir-Blodgett (LB) films of manganese octadecylphosphonate(Mn(O₃PC₁₈H₃₇)·H₂O)are prepared bydepositing octadecylphosphonate monolayers from aMnCl₂·4H₂O containing subphase at a pHrange of 5.2-5.6. Electron paramagnetic resonance (EPR) studies of the LB filmgive evidence for antiferromagnetic exchangein a two-dimensional inorganic extended lattice, in agreement withpublished magnetic studies of solid-statemanganese alkylphosphonates. The g values of the LBfilm are characteristic of Mn²⁺ in a nearly cubic fieldandare essentially isotropic, ranging from 1.99 to 2.00. Thedependence of the EPR line width on sample orientationin the magnetic field is consistent with the behavior predicted for atwo-dimensional lattice with antiferromagneticHeisenberg exchange. The temperature dependence of the integratedarea of the EPR signal, which is proportionalto spin susceptibility, is presented. A value for theantiferromagnetic exchange constant, J/k, of -2.8 Kwasdetermined for the LB film by fitting the data to a high temperatureseries expansion. This is in excellent agreementwith the J/k values obtained for the solid-state manganesephosphonates. EPR line widths of both the manganeseoctadecylphosphonate LB film and a powder sample of manganesepropylphosphonate increase rapidly astemperature is decreased below 30 K. This is characteristic of asystem approaching a magnetic ordering transitionand is caused by antiferromagnetic fluctuations. The solid-statemanganese alkylphosphonates undergoantiferromagnetic ordering transitions at temperatures in the range14.8-15.1 K, but an ordering transition in theLB film cannot be observed using EPR because the line width becomes toobroad and the signal is too weak tomeasure below 17 K. The study confirms that the in-plane structureof the manganese phosphonate LB film isthe same as that of the solid-state manganese phosphonateanalogs.