The Relationship Between Magnetic Interactions and Near Neighbor Interatomic Distances in the Transition Metal Sublattice of R(Mn/Fe)6A6 (R=Nd or Sm, A=Ge or Sn)

The magnetic and crystallographic structures of R(Fe/Mn)6A6 (R=Nd or Sm and A=Ge or Sn) intermetallics have been investigated using x-ray and neutron diffraction techniques and superconducting quantum interference device magnetic measurements. For both stannides (A=Sn) and germanides (A=Ge), the lattice contracts with increasing iron content. In the case of the stannides, substitution of manganese by iron enhances the saturation magnetization and Curie temperature at low iron concentrations (x≤2) suggesting the presence of an extremely rare occurrence, positive coupling between iron and manganese magnetic moments. In contrast, the magnetic properties of the germanides deteriorate rapidly as manganese is replaced by iron. This difference in the dependence of magnetic properties on the iron content between the germanides and stannides is explained using the Bethe–Slater relationship between near neighbor exchange interactions and interatomic distances. Based on the observations described in this article, it is concluded that the critical near neighbor interatomic distance above which manganese/iron moments couple positively in these intermetallics is ∼2.614 Å

The Relationship Between Magnetic Interactions and Near Neighbor Interatomic Distances in the Transition Metal Sublattice of R(Mn/Fe)₆A₆(R=Nd or Sm, A=Ge or Sn)

The magnetic and crystallographic structures of R(Fe/Mn)6A6 (R=Nd or Sm and A = Ge or Sn) intermetallics have been investigated using x-ray and neutron diffraction techniques and superconducting quantum interference device magnetic measurements. For both stannides (A = Sn) and germanides (A = Ge), the lattice contracts with increasing iron content. In the case of the stannides, substitution of manganese by iron enhances the saturation magnetization and Curie temperature at low iron concentrations (x ≤2 ) suggesting the presence of an extremely rare occurrence, positive coupling between iron and manganese magnetic moments. In contrast, the magnetic properties of the germanides deteriorate rapidly as manganese is replaced by iron. This difference in the dependence of magnetic properties on the iron content between the germanides and stannides is explained using the Bethe-Slater relationship between near neighbor exchange interactions and interatomic distances. Based on the observations described in this article, it is concluded that the critical near neighbor interatomic distance above which manganese/iron moments couple positively in these intermetallics is ∼2.614 Å.

The Atomic and Magnetic Structure of NdMn(6−x)FexGe6 Solid Solutions

The magnetic and crystallographic properties of induction-melted NdMn(6−x)FexGe6 intermetallics (x=0, 1.0, and 1.5) in the temperature range of 30–475 K have been studied by x-ray and neutron diffraction techniques and SQUID measurements. All of the samples crystallized in the YCo6Ge6-type structure (P6/mmm). A small amount (\u3c5 mol%) of Nd(MnFe)2Ge2 is present as an impurity. As expected, iron replaces manganese at the 3g site. The unit cell volume decreases slightly with increasing iron content at an average rate of 1.3% per substituted atom. Lattice parameters a and c contract at a rate of 0.6% and 0.2% per substitution atom, respectively. The net magnetization of these samples decreases rapidly with increasing iron content. According to neutron diffraction data, the magnetic moment of the iron sublattice couples negatively with ferromagnetically coupled manganese and neodymium moments. Addition of iron suppresses the spin reorientation processes observed in NdMn6Ge6. Whereas the net moment in NdMn5Fe1Ge6 slowly cants away from the c-axis with increasing temperature, the easy direction of NdMn4.5Fe1.5Ge6 is approximately parallel to the c-axis in the temperature range mentioned above

On a Pair of Diophantine Equations

For relatively prime natural numbers $a$ and $b$, we study the two equations $ax+by = (a-1)(b-1)/2$ and $ax+by+1= (a-1)(b-1)/2$, which arise from the study of cyclotomic polynomials. Previous work showed that exactly one equation has a nonnegative solution, and the solution is unique. Our first result gives criteria to determine which equation is used for a given pair $(a,b)$. We then use the criteria to study the sequence of equations used by the pair $(a_n/\gcd{(a_n, a_{n+1})}, a_{n+1}/\gcd{(a_n, a_{n+1})})$ from several special sequences $(a_n)_{n\geq 1}$. Finally, fixing $k \in \mathbb{N}$, we investigate the periodicity of the sequence of equations used by the pair $(k/\gcd{(k, n)}, n/\gcd{(k, n)})$ as $n$ increases.Comment: 21 pages, 2 figure

Legionella pneumonia as a cause of atypical pneumonia in a tertiary care hospital in Sri Lanka

Atypical pneumonia which contributes to an important proportion of community acquired pneumonia and Legionella pneumophila is a noteworthy pathogen worldwide. Legionnaires’ disease, the severe form of pneumonia is predominantly caused by Legionella pneumophila serogroup 1. This study was conducted to determine the presence of Legionella pneumophila as a pathogen and the associated risk factors among the patients admitted with atypical pneumonia to a tertiary care hospital in Sri Lanka. Seventy-five adult patients diagnosed with atypical pneumonia attending professorial medical unit of Colombo South Teaching Hospital, Sri Lanka were enrolled. Risk factors related to the disease was assessed by an interviewer administered questionnaire. Expectorated sputum was processed on supplemented buffered charcoal yeast extract medium and urine specimens were tested for Legionella pneumophila serogroup 1 antigen. Fifty-six percent of the patients were males and 91% were residing in urban areas. Smoking was admitted by 32% and that of alcohol consumption was in 25%. Composting and potting, distant travelling and frequent use of air conditioning was reported in 28%, 37% and 4% respectively. Majority of participants were not exposed to cooling towers, humidifiers or plumbing and not visited high risk areas. Among the study group, 21% had diabetes, 24% had ischaemic heart disease and 36% had chronic lung diseases. None of the sputum samples grew Legionella pneumophila, and all urine samples were negative for the antigen of Legionella pneumophila serogroup 1. It is concluded that, in this population of community acquired atypical pneumonia, Legionella pneumophila was not identified as a causative agent. KEYWORDS: Atypical pneumonia, community acquired pneumonia, Legionella pneumophil

The Atomic and Magnetic Structure of NdMn(₆₋ₓ)FeₓGe₆ Solid Solutions

The magnetic and crystallographic properties of induction-melted NdMn(6-x)FexGe6 intermetallics (x = 0, 1.0, and 1.5) in the temperature range of 30-475 K have been studied by x-ray and neutron diffraction techniques and SQUID measurements. All of the samples crystallized in the YCo6Ge6-type structure (P6/mmm). A small amount ( \u3c 5 mol%) of Nd(MnFe)2Ge2 is present as an impurity. As expected, iron replaces manganese at the 3g site. The unit cell volume decreases slightly with increasing iron content at an average rate of 1.3% per substituted atom. Lattice parameters a and c contract at a rate of 0.6% and 0.2% per substitution atom, respectively. The net magnetization of these samples decreases rapidly with increasing iron content. According to neutron diffraction data, the magnetic moment of the iron sublattice couples negatively with ferromagnetically coupled manganese and neodymium moments. Addition of iron suppresses the spin reorientation processes observed in NdMn6Ge6. Whereas the net moment in NdMn5Fe1Ge6 slowly cants away from the c-axis with increasing temperature, the easy direction of NdMn4.5Fe1.5Ge6 is approximately parallel to the c-axis in the temperature range mentioned above

A Magnetic and Crystallographic Study of (Sm/Gd)₂(Fe/Si)₁₇C\u3csub\u3ez\u3c/sub\u3e Solid Solutions

The crystallographic and magnetic properties of SmyGd2-yFe17-xSix (0 ≤ x ≤ 3 and y = 1 and 1.5) solid solutions and their interstitial carbides have been investigated using x-ray diffraction and magnetic measurements. The SmyGd2-yFe17-xSix samples crystallized in the rhombohedral Th2Zn17 structure with less than 5 mol % of impurities. The unit cells of the mixed rare-earth (R) samples are smaller than those of Sm2Fe17 and Gd2Fe17. The carbided samples contain up to a total of 15 mol % of free iron, an iron suicide, and/or cubic Si5C3. The unit cells of the carbided samples are 1%-4% larger than those of the parent samples. For a given silicon concentration, the Curie temperatures (Tc) of SmyGd2-yFe17-xSix intermetallics are higher than those of the two end members. For example, the Tc of SmGdFe17 (280°C) is approximately 160° and 80° higher than that of Sm2Fe17 and Gd2Fe17, respectively. The Tc measured for the SmyGd2-yFe17-xSx samples, 280-290°C, are among the highest values observed for a R2Fe17-xMx intermetallic where M is a substituent other than cobalt. Except in the case of SmGdFe16SiCz (z unknown), the Tc of the carbided samples are 20%-25% higher than those of the parent samples. A Tc of 426°C and a magnetization of 120.6 emu/g observed for SmGdFe16SiCz are the highest values measured for the intermetallics investigated herein. As determined by x-ray diffraction studies of magnetically aligned samples, the easy axis of magnetization is parallel to the c axis

Crystal and Magnetic Structures of LaNi5−xMnx

The crystallographic and magnetic properties of LaNi5−xMnx with x=1, 1.5, and 2, have been investigated using x-ray and neutron diffraction, vibrating sample magnetometer and superconducting quantum interference device measurements. All the samples crystallize in the hexagonal CaCu5-type (P6/mmm) structure. Manganese atoms preferentially occupy the 3g site in the LaNi5 structure. The bulk magnetization of the LaNi5−xMnx powder samples decreases rapidly as nickel is replaced by manganese. A ferrimagnetic model is applied to describe the magnetic structure of the LaNi5−xMnx samples for x=1.5 and 2. A ferromagnetic model gives the best fit of the neutron diffraction data for the LaNi4Mn sample

Oxygen and Phosphorus Coordination Around Iron in Crystalline Ferric Ferrous Pyrophosphate and Iron-phosphate Glasses with UO₂ or Na₂O

Fe K-edge x-ray absorption fine-structure (XAFS) measurements were performed on glass samples of (Fe3O4)0.3(P2O5)0.7 with various amounts of Na2O or UO2. Near-edge and extended-XAFS regions are studied and comparisons are made to several reference compounds. We find that iron in the base glass is ~25% divalent and that the Fe2+ coordination is predominantly octahedral, while Fe3+ sites are roughly split between tetrahedral and octahedral coordinations. Also, we measure roughly one FeñOñP link per iron. Substitution of Na2O or UO2 up to 15 mo1% primarily affects the first FeñO shell. The results are compared to data from the related material Fe3(P2O7)2