The major importance of surface atoms in small nanoparticles (NPs) offers the opportunity to tailor the magnetic properties by playing with the interface between nanomagnet and its surrounding. The system FeRh has attracted a lot of attention because, when it is in the chemically ordered B2 phase (CsCl-like), it presents an antiferromagnetic to ferromagnetic order (AFM-FM) transition close to room temperature. Recently for epitaxially grown FeRh films both strain and field effects from an underneath BaTiO3 ferroelectric crystal has been exploited to electrically drive, with only few volts, the FeRh metamagnetic transition temperature (just above room temperature) 1. This paper deal with structural and intrinsic magnetic properties of FeRh nanoclusters, prepared using Mass-Selected Low Energy Cluster Beam Deposition (MS-LECBD) available at the PLYRA platform of Institut Lumière Matière at Lyon. In sharp contrast to film and bulk studies, we have put into evidence the persistence of FM order down to 3 K (ferromagnetic alignment of the Fe and Rh magnetic moments of respectively 3 and 1 μB per atom) in size-selected 3.3 nm diameter FeRh clusters crystallized in the B2 phase 2. This anomalous magnetic order has been ascribed to finite size induced structural relaxation. Very recently, FeRh nanoclusters have been deposited on a crystalline BaTiO3 layer epitaxially grown on a Nb-doped SrTiO3 layer, using a MBE technique (at INL-ECL). Grazing incidence x-ray diffraction measurements (GIXRD, on the BM32 beamline at ESRF) have been performed on different particle sizes thanks to the size-selection capabilities of the MS-LECBD setup. The epitaxial relationships FeRh//BaTiO3 and FeRh//BaTiO3 were determined by X-Ray Diffraction (XRD), with a possible lattice parameter variation for FeRh NPs. One can underline that it is the first evidence of epitaxial relationship between the faces of nano-crystallites pre-formed in gas phase and a mono-crystalline oxide surface. Moreover, these specific interface coupling between FeRh clusters and the BaTiO3 surface would pave the way towards the manipulation of the atomic structure, and hence the magnetic properties, through a voltage-driven control of the ferroelectric (and piezoelectric) substrate.
1 R. O. Cherifi et al., Nature Materials 13, 345–351 (2014)
2 A. Hillion et al., Phys. Rev. Letters 110, 087207 (2013)