Stress modulated antiferromagnetism in a BiFeO3-based thin film

In the challenge to develop new, high density logic and memory devices, the concept of employing electron spin transport as the data vector (i.e. spintronics) is of great interest due to the potential for very low energy consumption devices.<br /> <br /> Antiferromagnetic materials play a pivotal role in many current and envisioned spintronic devices through the phenomenon of magnetic exchange bias at the interface between a ferromagnet and an antiferromagnet. This phenomenon allows such heterostuctures to act as spin-valves to control the conduction of electrons according to their spin. The ability to modulate the exchange bias, for example by switching the antiferromagnetism on and off, would be a valuable concept in spintronic device design. <br /> <br /> The aim of this experimental PhD project is to investigate the phenomenon of pressure modulated antiferromagnetism, focusing on thin films of BiFeO3-PbTiO3 (BFPT) in order to assess its viability for spintronic devices. Piezoelectricity will be employed, both in selected substrates and in the BFPT itself, to provide the required stress/strain modulation in the material.

<p>In the challenge to develop new, high density logic and memory devices, the concept of employing electron spin transport as the data vector (i.e. spintronics) is of great interest due to the potential for very low energy consumption devices. Antiferromagnetic materials play a pivotal role in many current and envisioned spintronic devices through the phenomenon of magnetic exchange bias at the interface between a ferromagnet and an antiferromagnet. This phenomenon allows such heterostuctures to act as spin-valves to control the conduction of electrons according to their spin. The ability to modulate the exchange bias, for example by switching the antiferromagnetism on and off, would be a valuable concept in spintronic device design. </p> <p>We have previously demonstrated that in the perovskite oxide solid solution (1-x)BiFeO₃-xPbTiO₃, the antiferromagnetic Néel temperature drops from above room temperature to below room temperature on crossing the phase boundary between rhombohedral and tetragonal symmetry at x = 0.3 [1]. We have also shown that in particulate samples, the symmetry can be switched from tetragonal to rhombohedral with an isostatic pressure of 0.6 GPa, with the result that at room temperature the pressure changes the phase from antiferromagnetic to paramagnetic, i.e. stress turns the antiferromagnetism on or off [2].</p> <p>The aim of this PhD project is to further investigate the phenomenon of pressure modulated antiferromagnetism, focusing on thin films in order to assess its viability for spintronic devices. Piezoelectricity will be employed, both in selected substrates and in the BiFeO₃-PbTiO₃ itself, to provide the required stress/strain modulation in the material. The project will comprise the following objectives:<br /> (i) deposition and characterization of epitaxial BiFeO₃-PbTiO₃ on a single crystal piezoelectric substrate;<br /> (ii) study of the antiferromagnetism in the BiFeO₃-PbTiO3 films and its modulation by stress from the piezoelectric actuation of the substrate;<br /> (iii) deposition of epitaxial BiFeO₃-PbTiO₃ on substrates selected to provide favourable lattice matching for characterization of the ferroelectric & piezoelectric properties of the BiFeO₃-PbTiO₃ films;<br /> (iv) investigation of direct electrical modulation of antiferromagnetism by ferroelectric phase switching in BiFeO₃-PbTiO₃ films;<br /> (v) demonstration and characterization of the modulation of exchange bias using the above effects;<br /> (vi) evaluation of the outlook for devices based on the observed phenomena.</p> <p>[1] T.P. Comyn, T. Stevenson, M. Al-Jawad, S.L. Turner, R.I. Smith, W.G. Marshall, A.J. Bell and R. Cywinski, Phase-specific magnetic ordering in BiFeO₃− PbTiO₃, Appl. Phys. Lett. 93, 232901 (2008)<br /> [2] T.P. Comyn, T. Stevenson, M. Al-Jawad, W.G. Marshall, R.I. Smith, J. Herrero-Albillos, R. Cywinski and A.J. Bell, Pressure induced para-antiferromagnetic switching in BiFeO₃–PbTiO₃ as determined using in-situ neutron diffraction, J. Appl. Phys. 113, 183910 (2013)<br />  </p>

<p>Formal applications for research degree study should be made online through the <a href="https://www.leeds.ac.uk/research-applying/doc/applying-research-degrees">University's website</a>. Please state clearly in the Planned Course of Study section that you are applying for <em><strong>PHD Physics & Astronomy</strong></em> and in the research information section that the research degree you wish to be considered for is <em><strong>Stress modulated antiferromagnetism in a BiFeO₃-based thin film</strong></em> as well as <a href="https://eps.leeds.ac.uk/physics/staff/4118/dr-thomas-moore">Dr Thomas Moore</a> as your proposed supervisor. Please state clearly in the Finance Section that the funding source you are applying for is <em><strong>School of Physics & Astronomy Studentship: 2025/26.</strong></em></p> <p>Applications will be considered after the closing date.  Potential applicants are strongly encouraged to contact the supervisors for an informal discussion before making a formal application.  We also advise that you apply at the earliest opportunity as the application and selection process may close early, should we receive a sufficient number of applications or a suitable candidate is appointed.</p> <p><strong>Please note that you must provide the following documents in support of your application by the closing date of Tuesday 15 July 2025:</strong></p> <ul> <li>Full Transcripts of all degree study or if in final year of study, full transcripts to date</li> <li>Personal Statement outlining your interest in the project</li> <li>CV</li> </ul> <p>If English is not your first language, you must provide evidence that you meet the University's minimum English language requirements (below).</p> <p><em>As an international research-intensive university, we welcome students from all walks of life and from across the world. We foster an inclusive environment where all can flourish and prosper, and we are proud of our strong commitment to student education. Across all Faculties we are dedicated to diversifying our community and we welcome the unique contributions that individuals can bring, and particularly encourage applications from, but not limited to Black, Asian, people who belong to a minority ethnic community, people who identify as LGBT+ and people with disabilities. Applicants will always be selected based on merit and ability.</em></p>

Applicants to research degree programmes should normally have at least a first class or an upper second class British Bachelors Honours degree (or equivalent) in an appropriate discipline. The criteria for entry for some research degrees may be higher, for example, several faculties, also require a Masters degree. Applicants are advised to check with the relevant School prior to making an application. Applicants who are uncertain about the requirements for a particular research degree are advised to contact the School or Graduate School prior to making an application.

The minimum English language entry requirement for research postgraduate research study is an IELTS of 6.0 overall with at least 5.5 in each component (reading, writing, listening and speaking) or equivalent. The test must be dated within two years of the start date of the course in order to be valid. Some schools and faculties have a higher requirement.

<p>A highly competitive School of Physics & Astronomy Studentship, providing the award of full academic fees, together with a tax-free maintenance grant at the standard UKRI rate of £20,780 per year for 3.5 years. </p> <p>You will be responsible for paying the overtime fee in full in your writing up/overtime year (£340 in Session 2025/26), but the scholarship maintenance allowance will continue to be paid for up to 6 months in the final year of award.</p> <p>Please refer to the <a href="https://www.ukcisa.org.uk/">UKCISA</a> website for information regarding Fee Status for Non-UK Nationals.</p>

<p>For further information about your application, please contact PGR Admissions by e-mail to <a href="mailto:phd@engineering.leeds.ac.uk">phd@engineering.leeds.ac.uk</a></p> <p>For further information about this project, please contact Dr Thomas Moore by e-mail to <a href="mailto:T.A.Moore@leeds.ac.uk">T.A.Moore@leeds.ac.uk</a></p>