N+ Irradiation and Substrate-Induced Variability in the Metamagnetic Phase Transition of FeRh Films

Abstract

Metamagnetic FeRh has been the focus of numerous studies for its highly unique antiferromagnetic (AF) to ferromagnetic (FM) metamagnetic transition. While this phase transition usually occurs above room temperature (often Tc > 400 K), both ion irradiation and strained epitaxial growth have been used to bring it to applicable temperatures. Nevertheless, cross sample variability is pervasive in these studies. Here we explore the optical and magnetic properties of 35 nm thick FeRh grown by magnetron sputter deposition simultaneously on two different single crystal substrates: epitaxially on MgO (001) and highly strained with large lattice mismatch on Al2O3 (1000). We then irradiate the epitaxial film with 5 keV N+ ions to introduce disorder (and to a lesser extent, modify chemical composition) without effecting the surface morphology. We find that the phase-transitional properties of both films are strikingly different due to the large lattice mismatch, despite being grown in tandem with nominally identical growth conditions including Fe/Rh stoichiometry, pressure, and temperature. We observe that N+ implantation lowers Tc by ~60 K, yielding a sample with nominally the same transition temperature as the non-epitaxial film on sapphire, yet with a significantly increased magnetic moment, a larger magnetization change and a more abrupt transition profile. We attribute these differences to the Volmer-Weber type growth mode induced by the sapphire substrate and the resulting rougher surface morphology.

Domain state exchange bias in a single layer FeRh thin film formed via low energy ion implantation

“…For the He + implanted film, the loop is shifted up in moment and this is due to the higher penetration depth of He + into the film and therefore a larger background ferromagnetic moment due to a greater volume of FeRh in the FM state. These results are consistent with our prior work on the effects of ion implantation on FeRh, 11,[14][15][16]22 and stem from the introduction of atomic level defects, especially vacancies and interstitial pairs, that reduce the spin-flip energy of the system, thus driving down the metamagnetic transition temperature.…”

“…[11][12][13] Moreover, the metamagnetic transition temperature T M of FeRh is tailorable via doping and irradiation. [14][15][16] In theory, these features of FeRh suggest that AF/FM bilayer (or multilayer) stacks can be fabricated in FeRh films, and both its high-speed Ne ´el vector alignment and metamagnetic transition could serve as dynamic controls. Thus, the next step to make FeRh systems standout for spintronic applications will be the ability to introduce and tailor an exchange bias field at the AF/ FM interface.…”

A Three-Dimensional Analysis of Magnetic Nanopattern Formation in FeRh Thin Films on MgO Substrates: Implications for Spintronic Devices

“…Recently, several studies have been published on tailoring the magnetic and structural properties of FeRh by ion irradiation. A wide variety of ions and energies such as 30 keV Ga + , 1 MeV proton, 20 keV Ne + , 120 keV Ne + , 10 MeV I + , , 50 keV Ar + , 5 keV N + , or 3.8 keV He + were applied to manipulate the FM–AFM, FM–PM transition, as well as to induce the B2 → A1 structural transformation. By the manipulation of magnetic phases using 25 keV Ne + irradiation, simultaneous coexistence of three magnetic phases (FM, PM, and AFM) was demonstrated .…”