Seminar on 21 February 2019

CEITEC BUT, Brno University of Technology, Brno, Czech Republic
Imaging of asymmetric magnetic phase transition in FeRh structures
at 13:00 in Seminar room F052

The advantage of ferromagnetic materials is the nonvolatility of the information encoded in the internal magnetic configuration, which can be used for memory storage, logic and sensing devices. Antiferromagnets are another class of magnetic materials that features nonvolatile magnetic ordering, yet its applications have been largely overlooked until recently [1]. In materials featuring a first-order metamagnetic phase transition between the antiferromagnetic (AF) and ferromagnetic (FM) states, the nature of the phase transition can be tuned by strain, pressure, chemical doping, temperature, as well as magnetic and electric fields, potentially offering very high recording densities and huge changes in the order parameters controlled with very low power.

Moreover, metamagnetic materials are outstanding candidates for finding and exploiting new functionalities and emergent phenomena on the mesoscale [2,3]. For instance, the transition from the AF order to FM order in sub-micron-wide FeRh wires becomes greatly asymmetric when comparing the heating and cooling cycles [3,4]. This recovery of the abrupt transition in nanostructures could allow low-energy, efficient routes to control magnetic properties, leading to potential applications, for instance, in spintronics. Using magnetic imaging via magnetic force microscopy, we investigated phase nucleation and switching as a function of temperature in micron and submicron sized FeRh structures, which can be linked to electrical transport measurements [3] probing the resistance as an order parameter.

Furthermore, we show the dynamic response of the electronic and magnetic order to ultrafast laser excitation can be followed by time-resolved photoemission electron spectroscopy [5], which unlike techniques probing the total magnetization in the sample provides a direct comparison to the dynamic response of the structural order.

[1] T. Jungwirth et al., Nature Mater. 11, 231 (2016).
[2] F. Pressacco et al., Sci. Rep. 6, 22383 (2016).
[3] V. Uhlíř et al., Nat. Commun. 7, 13113 (2016).
[4] J. A. Arregi et al., J. Phys. D: Appl. Phys. 51, 105001 (2018).
[5] F. Pressacco et al., Struct. Dyn. 5, 034501 (2018).