scholarly journals Magnetoelastic driven Negative Thermal Expansion in a Framework Antiferromagnet

2014 ◽  
Vol 70 (a1) ◽  
pp. C276-C276
Author(s):  
Paul Saines ◽  
Phillip Barton ◽  
Marek Jura ◽  
Kevin Knight ◽  
Anthony Cheetham
Keyword(s):  
Thermal Expansion ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Magnetic Structure ◽  
Magnetic Order ◽  
Variable Temperature ◽  
Negative Thermal Expansion ◽  
Orthorhombic Phase ◽  
Two Dimensions ◽  
Magnetic Interactions

Metal-organic frameworks (MOFs) have recently attracted great attention for their multiferroic, magnetocaloric and low dimensional magnetic order. These properties depend on the precise magnetic interactions in frameworks and a deeper understanding of the coupling between the lattice of these materials and their magnetic order is required to underpin the future developments of these promising compounds. Neutron diffraction is the ideal technique for such studies but its application to studies of the magnetic structure of MOFs has been limited to date due to challenges in solving the structure of these dilute yet complex magnetic compounds. We have recently examined the magnetic properties and structure of a new dicarboxylate framework, cobalt adipate, Co(C6H8O4), which adopts P21/c monoclinic symmetry.[1] This compound has been found to order antiferromagnetically at low temperature and fits to neutron diffraction data have shown it adopts Pb21/c magnetic symmetry. Its magnetic structure features sheets of Co cations coupled antiferromagnetically in two dimensions through carboxylate groups. The emergence of this order is accompanied by magnetoelastic coupling, which drives anisotropic negative thermal expansion along the a-axis at low temperature. This is the first evidence for such behaviour in a MOF and we find that both this behaviour and the spin orientation in this material are controlled by the presence of weak ferromagnetic dipole-dipole coupling between the layers of tetrahedral cobalt. Variable temperature high resolution synchrotron X-ray and neutron powder diffraction have also revealed that the monoclinic angle of Co adipate decreases on cooling, passing through a metrically orthorhombic phase without any indication of a phase transition. This unusual behaviour has been rationalised by examining the thermal expansion of the framework along its principal axis, highlighting the importance of such analysis in low symmetry materials.

Polymorphism in the negative thermal expansion material magnesium hafnium tungstate

2008 ◽  
Vol 23 (1) ◽  
pp. 210-213 ◽  
Author(s):  
Amy M. Gindhart ◽  
Cora Lind ◽  
Mark Green
Keyword(s):  
Phase Transition ◽  
Thermal Expansion ◽  
Variable Temperature ◽  
Negative Thermal Expansion ◽  
Orthorhombic Phase ◽  
High Energy ◽  
X Ray Diffraction ◽  
Space Group ◽  
Smooth Change ◽  
Energy Ball

Magnesium hafnium tungstate [MgHf(WO4)3] was synthesized by high-energy ball milling followed by calcination. The material was characterized by variable- temperature neutron and x-ray diffraction. It crystallized in space group P21/a below 400 K and transformed to an orthorhombic structure at higher temperatures. The orthorhombic polymorph adopted space group Pnma, instead of the Pnca structure commonly observed for other A2(MO4)3 materials (A = trivalent metal, M = Mo, W). In contrast, the monoclinic polymorphs appeared to be isostructural. Negative thermal expansion was observed in the orthorhombic phase with αa = −5.2 × 10−6 K−1, αb = 4.4 × 10−6 K−1, αc = −2.9 × 10−6 K−1, αV = −3.7 × 10−6 K−1, and αl = −1.2 × 10−6 K−1. The monoclinic to orthorhombic phase transition was accompanied by a smooth change in unit-cell volume, indicative of a second-order phase transition.

Magnetic Order in Quaternary NiMnGe:T (T = Cr, Ti) Compounds

2019 ◽  
Vol 289 ◽  
pp. 156-163
Author(s):  
Andrzej Szytuła ◽  
Stanislav Baran ◽  
Bogusław Penc ◽  
Andreas Hoser ◽  
Vladimir Dyakonov
Keyword(s):  
Simple Model ◽  
Neutron Diffraction ◽  
Magnetic Structure ◽  
Magnetic Order ◽  
Magnetic Interactions ◽  
Néel Temperature ◽  
Cr Content ◽  
Propagation Vector ◽  
Cr System ◽  
Ti Content

The work reports the results of neutron diffraction measurements of NiMnGe:T systems where T is Cr or Ti. All investigated compounds have the helicoidal magnetic structure with the propagation vector k = (ka,0,0). The values of the ka component decrease with increasing Cr content and increase with increasing Ti content. For all compounds, except the sample with x = 0.18 in Cr-system, the helicoidal order is stable up to the Néel temperature. The obtained data are analysed based on simple model in which the magnetic interactions are described by two exchange integrals J1 > 0 for first and J2 < 0 for second neighbouring moments. This model clears up different dependence of ka component in different systems.

Uniaxial negative thermal expansion and band renormalization in monolayer Td−MoTe2 at low temperature

2020 ◽  
Vol 101 (10) ◽  
Author(s):  
Yu Ge ◽  
Zhenyu Ding ◽  
Wenjie Meng ◽  
Jihao Wang ◽  
Yubin Hou ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Low Temperature ◽  
Negative Thermal Expansion

scholarly journals Giant anisotropic thermal expansion actuated by thermodynamically assisted reorientation of imidazoliums in a single crystal

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Zi-Shuo Yao ◽  
Hanxi Guan ◽  
Yoshihito Shiota ◽  
Chun-Ting He ◽  
Xiao-Lei Wang ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Single Crystal ◽  
Molecular Motion ◽  
Bulk Material ◽  
Shape Change ◽  
Variable Temperature ◽  
Negative Thermal Expansion ◽  
Formidable Challenge ◽  
Potential Applications ◽  
Molecular Cations

Abstract Materials demonstrating unusual large positive and negative thermal expansion are fascinating for their potential applications as high-precision microscale actuators and thermal expansion compensators for normal solids. However, manipulating molecular motion to execute huge thermal expansion of materials remains a formidable challenge. Here, we report a single-crystal Cu(II) complex exhibiting giant thermal expansion actuated by collective reorientation of imidazoliums. The circular molecular cations, which are rotationally disordered at a high temperature and statically ordered at a low temperature, demonstrate significant reorientation in the molecular planes. Such atypical molecular motion, revealed by variable-temperature single crystal X-ray diffraction and solid-state NMR analyses, drives an exceptionally large positive thermal expansion and a negative thermal expansion in a perpendicular direction of the crystal. The consequent large shape change (~10%) of bulk material, with remarkable durability, suggests that this complex is a strong candidate as a microscale thermal actuating material.

Variable-Temperature Microcrystal X-ray Diffraction Studies of Negative Thermal Expansion in the Pure Silica Zeolite IFR

2001 ◽  
Vol 123 (23) ◽  
pp. 5453-5459 ◽  
Author(s):  
Luis A. Villaescusa ◽  
Philip Lightfoot ◽  
Simon J. Teat ◽  
Russell E. Morris
Keyword(s):  
Thermal Expansion ◽  
Variable Temperature ◽  
Negative Thermal Expansion ◽  
X Ray Diffraction ◽  
X Ray ◽  
Pure Silica

Neutron diffraction study and anomalous negative thermal expansion in nonsuperconducting PrFe1−xRuxAsO

2012 ◽  
Vol 86 (5) ◽  
Author(s):  
Yuen Yiu ◽  
V. Ovidiu Garlea ◽  
Michael A. McGuire ◽  
Ashfia Huq ◽  
David Mandrus ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Neutron Diffraction ◽  
Diffraction Study ◽  
Negative Thermal Expansion ◽  
Neutron Diffraction Study

Low-Temperature Oxygen Migration and Negative Thermal Expansion in ZrW2-xMoxO8

2000 ◽  
Vol 122 (36) ◽  
pp. 8694-8699 ◽  
Author(s):  
J. S. O. Evans ◽  
P. A. Hanson ◽  
R. M. Ibberson ◽  
N. Duan ◽  
U. Kameswari ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Low Temperature ◽  
Negative Thermal Expansion ◽  
Oxygen Migration

scholarly journals Real-space imaging of the atomic-scale magnetic structure of Fe1+yTe

Science ◽  
2014 ◽  
Vol 345 (6197) ◽  
pp. 653-656 ◽  
Author(s):  
Mostafa Enayat ◽  
Zhixiang Sun ◽  
Udai Raj Singh ◽  
Ramakrishna Aluru ◽  
Stefan Schmaus ◽  
...  
Keyword(s):  
Magnetic Structure ◽  
Magnetic Order ◽  
Parent Compound ◽  
Iron Concentration ◽  
Orthorhombic Phase ◽  
Real Space ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Excess Iron

Spin-polarized scanning tunneling microscopy (SP-STM) has been used extensively to study magnetic properties of nanostructures. Using SP-STM to visualize magnetic order in strongly correlated materials on an atomic scale is highly desirable, but challenging. We achieved this goal in iron tellurium (Fe1+yTe), the nonsuperconducting parent compound of the iron chalcogenides, by using a STM tip with a magnetic cluster at its apex. Our images of the magnetic structure reveal that the magnetic order in the monoclinic phase is a unidirectional stripe order; in the orthorhombic phase at higher excess iron concentration (y > 0.12), a transition to a phase with coexisting magnetic orders in both directions is observed. It may be possible to generalize the technique to other high-temperature superconductor families, such as the cuprates.

scholarly journals Negative thermal expansion of HTSC-type structures: low temperature structure measurements on Eu1+x(Ba1−yRy)2−xCu3O7−d compounds and theoretical treatment

2005 ◽  
Vol 31 (3) ◽  
pp. 263-267 ◽  
Author(s):  
V. V. Eremenko ◽  
S. B. Feodosyev ◽  
I. A. Gospodarev ◽  
V. A. Sirenko ◽  
M. Yu. Shvedun ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Low Temperature ◽  
Negative Thermal Expansion ◽  
Theoretical Treatment ◽  
Temperature Structure
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