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SUMMARY:Effects of $^{18}$O isotope substitution in multiferroic $R$MnO$_3
 $ ($R$=Tb\, Dy)
DTSTART;VALUE=DATE-TIME:20160204T223000Z
DTEND;VALUE=DATE-TIME:20160204T224500Z
DTSTAMP;VALUE=DATE-TIME:20260809T065657Z
UID:indico-contribution-478@events01.synchrotron.org.au
DESCRIPTION:Speakers: Paul Graham (University of New South Wales)\nMultife
 rroic materials demonstrate desirable attributes for next-generation multi
 functional devices as they exhibit coexisting ferroelectric and magnetic o
 rders. In type-II multiferroics\, coupling exists that allows ferroelectri
 city to be manipulated via magnetic order and vice versa\, offering potent
 ial in high-density information storage and sensor applications. Despite e
 xtensive investigations into the subject\, questions of the physics of mag
 netoelectric coupling in multiferroics remain\, and competing theories pro
 pose different mechanisms. The aim of this investigation was to study chan
 ges in the statics and dynamics of structural\, ferroelectric and magnetic
  orders with oxygen-18 isotope substitution to shine light into the coupli
 ng mechanism in multiferroic $R$MnO3 ($R$=Tb\, Dy) systems.\n\nWe have per
 formed Raman spectroscopy on $^{16}$O and $^{18}$O-substituted TbMnO3 sing
 le crystals. Oxygen-18 isotope substitution reduces all phonon frequencies
  significantly. However\, specific heat measurements determine no changes 
 in Mn$^{3+}$ (28 and 41 K) magnetic phase transition temperatures. Pronoun
 ced anomalies in peak position and linewidth at the magnetic and ferroelec
 tric phase transitions. While the anomalies at the sinusoidal magnetic pha
 se transition (41 K) are in accordance to the theory of spin-phonon coupli
 ng\, further deviations develop upon entering the ferroelectric phase (28 
 K). Furthermore\, neutron diffraction measurements on $^{16}$O and $^{18}$
 O-substituted DyMnO$_{3}$ powders show structural deviations at the ferroe
 lectric phase transition (17 K) in the order of 100 fm in the $b$ directio
 n. The $Pbnm$ space group is centrosymmetric and therefore does not allow 
 ferroelectricity via atomic displacements\, however our Reitveld analysis 
 for the subgroup P2$_1$ shows significant displacements and polarisation a
 long $b$ that is comparable to the experimental value\, making it the most
  promising candidate for ionic displacement induced polarisation in DyMnO$
 _{3}$. These combined results demonstrate that structure is an important c
 onsideration in the emergence of ferroelectricity in these materials.\n\nh
 ttps://events01.synchrotron.org.au/event/19/contributions/478/
LOCATION:
URL:https://events01.synchrotron.org.au/event/19/contributions/478/
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