Final Report Summary - MULTI-FUNC-MATERIALS (Quest for novel Multi-functional Oxides: Synthesis, bulk properties, and their microscopic origins)
Project context and objectives
The overall aim of the project was to discover new magneto-electric multiferroics, i.e. compounds that exhibit simultaneously both magnetic order and ferro-electricity and whose magnetic and dielectric properties are strongly coupled. The specific objectives were:
(i) to perform exploratory synthesis and crystal growth of a number of target materials;
(ii) to characterise the magnetic and dielectric bulk properties of these materials, including the construction of an apparatus capable of measuring magneto-electric susceptibility;
(iii) to carry out neutron-scattering measurements at European facilities to probe crystal and magnetic structures. See the project website - http://xray.physics.ox.ac.uk/Boothroyd/Multiferroics.htm - for more details.
Typical routes for the synthesis of new multiferroic materials include the incorporation of magnetic and non-magnetic (with empty d shells) transition metals in the form of mixed perovskites, geometrically frustrated systems, charge ordered systems, or antiferromagnets with specific collinear (G type) or non-collinear spiral spin systems. Around 40 compounds were synthesised using the solid-state ceramic method, to try and stabilise compounds wherein at least one of these microscopic mechanisms would hold good. Single crystal growth was attempted on the more promising among these systems, using a floating zone furnace.
The outcome of this large sample synthesis effort has been very satisfactory, since four new multiferroics were synthesised during the course of this fellowship. These are the brownmillerite phase Ca2Fe2O5, the double perovskites Y2MnCoO6 and Y2MnNiO6, and Cu3Nb2O8. A detailed report of the synthesis and properties of Cu3Nb2O8 has been published (Cu3Nb2O8: A Multiferroic with Chiral Coupling to the Crystal Structure; R. D. Johnson, Sunil Nair, L. C. Chapon, A. Bombardi, C. Vecchini, D. Prabhakaran, A. T. Boothroyd, and P. G. Radaelli; Phys. Rev. Lett. 107, 137205 (2011)).
An apparatus was constructed during the course of this fellowship to enable the direct measurement of the magneto-electric susceptibility. This was based on a method to directly measure the change in magnetisation driven by the application of an external electric field. The measurement probe was installed in a helium cryostat. Tests showed that the apparatus worked well, and with some fine-tuning and the development of the control software it should provide a very useful capability in the host's laboratory.
Project outcomes
The fellowship enabled the applicant to gain extensive experience in sample synthesis and single crystal growth, and the use of large-scale facilities for neutron and synchrotron experiments. Since such large-scale facilities are not available in the applicant's home country, the benefits derived from this research will prove invaluable. The benefit of this research tenure is also borne out by the fact that, on his return to his home country, the fellowship holder has taken up a permanent faculty position in a new Science University in Pune, where he is currently in the process of setting up a laboratory for the synthesis of novel materials.
The impact of this work can be gauged by the fact that the discovery of multiferroicity in Cu3Nb2O8 by the fellowship holder has been published in the Physical Review Letters journal. Details of the other three newly discovered multiferroic materials will be reported in due course. Investigations of new multifunctional oxides are at the forefront of current research in condensed matter physics, and the output from this fellowship is expected to add significantly to worldwide research efforts in this direction.
The overall aim of the project was to discover new magneto-electric multiferroics, i.e. compounds that exhibit simultaneously both magnetic order and ferro-electricity and whose magnetic and dielectric properties are strongly coupled. The specific objectives were:
(i) to perform exploratory synthesis and crystal growth of a number of target materials;
(ii) to characterise the magnetic and dielectric bulk properties of these materials, including the construction of an apparatus capable of measuring magneto-electric susceptibility;
(iii) to carry out neutron-scattering measurements at European facilities to probe crystal and magnetic structures. See the project website - http://xray.physics.ox.ac.uk/Boothroyd/Multiferroics.htm - for more details.
Typical routes for the synthesis of new multiferroic materials include the incorporation of magnetic and non-magnetic (with empty d shells) transition metals in the form of mixed perovskites, geometrically frustrated systems, charge ordered systems, or antiferromagnets with specific collinear (G type) or non-collinear spiral spin systems. Around 40 compounds were synthesised using the solid-state ceramic method, to try and stabilise compounds wherein at least one of these microscopic mechanisms would hold good. Single crystal growth was attempted on the more promising among these systems, using a floating zone furnace.
The outcome of this large sample synthesis effort has been very satisfactory, since four new multiferroics were synthesised during the course of this fellowship. These are the brownmillerite phase Ca2Fe2O5, the double perovskites Y2MnCoO6 and Y2MnNiO6, and Cu3Nb2O8. A detailed report of the synthesis and properties of Cu3Nb2O8 has been published (Cu3Nb2O8: A Multiferroic with Chiral Coupling to the Crystal Structure; R. D. Johnson, Sunil Nair, L. C. Chapon, A. Bombardi, C. Vecchini, D. Prabhakaran, A. T. Boothroyd, and P. G. Radaelli; Phys. Rev. Lett. 107, 137205 (2011)).
An apparatus was constructed during the course of this fellowship to enable the direct measurement of the magneto-electric susceptibility. This was based on a method to directly measure the change in magnetisation driven by the application of an external electric field. The measurement probe was installed in a helium cryostat. Tests showed that the apparatus worked well, and with some fine-tuning and the development of the control software it should provide a very useful capability in the host's laboratory.
Project outcomes
The fellowship enabled the applicant to gain extensive experience in sample synthesis and single crystal growth, and the use of large-scale facilities for neutron and synchrotron experiments. Since such large-scale facilities are not available in the applicant's home country, the benefits derived from this research will prove invaluable. The benefit of this research tenure is also borne out by the fact that, on his return to his home country, the fellowship holder has taken up a permanent faculty position in a new Science University in Pune, where he is currently in the process of setting up a laboratory for the synthesis of novel materials.
The impact of this work can be gauged by the fact that the discovery of multiferroicity in Cu3Nb2O8 by the fellowship holder has been published in the Physical Review Letters journal. Details of the other three newly discovered multiferroic materials will be reported in due course. Investigations of new multifunctional oxides are at the forefront of current research in condensed matter physics, and the output from this fellowship is expected to add significantly to worldwide research efforts in this direction.
