TITLE: Non-collinear Magnetism in Co doped Hexaferrites. The search for room temperature multiferroics.
AUTHOR: Stuart Cavill, York University (UK)
INVITED BY: Silvia Gallego (ICMM)
DAY of the talk: September, 3 (Thursday) at 12PM
PLACE: Sala de Seminarios, ICMM-CSIC
ABSTRACT: The search for room temperature (RT) magnetoelectric materials is an important area of research covering both fundamental and technological endeavours. For the latter, such a material could have applications in next generation low power ICT devices including both data storage and voltage tuneable microwave filters. The key driver in this field is to find materials that are both ferroelectric and ferromagnetic simultaneously, with a strong coupling between the order parameters. To display ferroelectricity and magnetism simultaneously, both the spatial inversion and time reversal symmetries must be broken. The magnetic ordering of a material is one way that this can be achieved and whist a multitude of magnetic orders exist, the transverse conical magnetic ordering (that contains a cycloidal component) allows both symmetries to be broken simultaneously. Identifying a RT transverse conical ordering in a material is therefore a key first step in the search for a RT multiferroic. Co containing hexaferrites are an interesting set of complex oxide materials that allow a departure from the usual magnetic uniaxial behaviour found in the undoped parent compounds. In this seminar I will discuss our recent studies on single crystals of the Co-Ti doped M-type hexaferrite SrCo1.2Ti1.2Fe9.6O19 and the W-type hexaferrite SrCo2Fe16O27 employing soft X-ray resonant diffraction at the Co and Fe L3 edges. Using a variety of field geometries and polarization analysis of the scattered beam, I will show that the magnetic structure present in these materials is transverse conical at room temperature and therefore present candidate systems for further study into their magnetoelectric properties.
