Benjamin Byrant: Probing Multiferroic Domain Walls with Scanning Probe Microscopy

Materials with ferroic order – ferromagnetic, ferroelectric or ferroelastic – are naturally organised into domains, separated by domain walls where the ferroic order changes sign. Domain walls may have characteristics distinct from the bulk material, for example conductive domain walls in a bulk insulator, or walls with a net magnetic moment in an antiferromagnetic material. Scanning probe microscopy provides an ideal method for probing these unique local properties, due to its high spatial resolution and diverse detection modes, such as Magnetic Force Microscopy, Piezoresponse Force Microscopy and Conductive AFM.

Domain walls in multiferroic materials, which possess more than one ferroic order, are particularly interesting, since one may observe coupling of order parameters at the domain wall. I will outline some recent results on the multiferroic charge-ordered layered manganite Pr(Sr0.1Ca0.9)2Mn2O7. In this material, boundaries between charge-order domains, with a p shift in the charge order pattern, may be observed via Microwave Impedance Microscopy. These charge-order domain walls, which in this material are also ferroelectric domain walls, are more conductive than the bulk material due to local lifting of the charge order [1].

By employing Scanning Probe techniques such as Magnetic Force Microscopy and Conductive AFM in high magnetic fields, we can see how the morphology and local properties of domain walls change when the material undergoes a magnetic field induced phase transition. However, in multiferroics these transitions may occur at fields of 20 T or more, and to date most scanning probe facilities have been limited to less than 10 T. Therefore, to enable high-field studies of the mesoscopic magnetic and electronic properties of multiferroics - and other materials - we are developing a versatile Scanning Probe Microscope for operation at up to 38 T at the High Field Magnet Lab.

[1] E. Y. Ma, B. Bryant, Y. Tokunaga, G. Aeppli, Y. Tokura, and Z.-X. Shen, “Charge-order domain walls with enhanced conductivity in a layered manganite,” Nat. Commun., 6, 7595, 2015.