Role of interface quality for the spin Hall magnetoresistance in nickel ferrite thin films with bulk-like magnetic properties

Abstract

We utilize spin Hall magnetoresistance (SMR) measurements to experimentally investigate the pure spin current transport and magnetic properties of nickel ferrite (NiFe 2 O 4 ,NFO)/normal metal (NM) thin film heterostructures. We use (001)-oriented NFO thin films grown on lattice-matched magnesium gallate substrates by pulsed laser deposition, which significantly improves the magnetic and structural properties of the ferrimagnetic insulator. The NM in our experiments is either Pt or Ta. A comparison of the obtained SMR magnitude for charge currents applied in the [100]-and [110]direction of NFO yields a change of 50% for Pt at room temperature. We also investigated the temperature dependence of this current direction anisotropy and find that it is qualitatively different for the conductivity and the SMR magnitude. From our results we conclude that the observed current direction anisotropy may originate from an anisotropy of the spin mixing conductance or of the spin Hall effect in these Pt and Ta layers, and/or additional spin-galvanic contributions from the NFO/NM interface.The advent of (spin) angular momentum transport without an accompanying charge current, i.e. the flow of pure spin currents, has led to the discovery of several remarkable effects that are relevant for next generation spin electronic devices 1-3 . Amongst these effects is the spin Hall magnetoresistance 3-9 in magnetically ordered insulator (MOI)/ normal metal (NM) heterostructures, which enables the detection of novel magnetic phases in MOIs 10-12 . While initial investigations of the SMR heavily relied on yttrium iron garnet (YIG), the report on the observation of the SMR in many other MOIs ranging from ferrimagnetic 5,13,14 to antiferromagnetic [15][16][17][18][19] order confirms the universality of this effect. The magnitude of the SMR effect crucially depends on the transparency of the MOI/NM interface as well as the spin Hall effect (SHE) and the spin diffusion length of the NM. Nevertheless, the impact of the current direction with respect to the crystalline orientations on the SMR remains up to now unexplored. In this publication we experimentally show that the SMR amplitude in nickel ferrite thin films with bulk-like magnetic properties 20 interfaced with Ta or Pt depends upon the relative orientation of the charge current j compared to the NFO crystal axes.The heterostructures investigated in this study are NFO/NM bilayers, where the NM is Pt and Ta. The ferrimagnetic NFO thin films (≈ 100 nm) are grown on (001)-oriented MgGa 2 O 4 (MgGO) substrates via pulsed laser deposition. The bulk MgGO single crystals were obtained by the Czochralski method at the Leibniz-Institut für Kristallzüchtung, Berlin, Germany 21 , and substrates were then prepared by CrysTec GmbH, Berlin, Germany. During growth the substrate was kept at 700 • C in an oxygen atmosphere with 10 mTorr. For a) Electronic mail: matthias.althammer@wmi.badw.de the magnetotransport experiments we then defined NM Hall bar structures on top of the NFO with a width of 80 µm and a...

Strain induced anisotropy in liquid phase epitaxy grown nickel ferrite on magnesium gallate substrates

“…In another study, the in-plane tensile strain in a 4 m thick YIG film on 1 mm thick YAG substrate grown by CVD techniques at 1250 C was also accounted for by the mismatch in 37 . In this study NFO films were grown on MGO at ~ 850C and annealed at 1000 C. The thermal expansion coefficient = 13.4 × 10 –6 /C for NFO is 40% higher than = 9.5 × 10 –6 /C for MGO 27 , 38 , 39 . The mismatch in -values, therefore, appears to be the cause of an unexpected increase in both the in-plane tensile strain and out-of-plane compressive strain as the film thickness and its volume are increased.…”

Static magnetic proximity effects and spin Hall magnetoresistance in Pt/Y3Fe5O12 and inverted Geprägs1, Klewe2, Meyer3 et al. 2020Phys. Rev. BSelf Cite12040View full textAdd to dashboardCite

“…This characteristic angle dependence is inconsistent with the conventional AMR of a polycrystalline HM layer [32] and is, instead, explained by an interplay of charge and spin currents at the interface between the FMI and the HM layer via the (inverse) SHE [33]. This so-called spin Hall magnetoresistance (SMR) was further experimentally confirmed in a variety of HM/FMI heterostructures such as Pt/YIG [31,32,[34][35][36][37][38], Ta/YIG [35], Pt/Gd 3 Fe 5 O 12 [39], Pt/Fe 3 O 4 [32], Pt/NiFe 2 O 4 [32,40], Pt/CoFe 2 O 4 [41], and Pt/Cu 2 OSeO 3 [42] as well as using antiferromagnetic insulators NiO [43][44][45][46], Cr 2 O 3 [47,48], and α-Fe 2 O 3 [46,[49][50][51]. The exchange of spin angular momentum as the underlying mechanism of the SMR is further confirmed by Pt/YIG/Pt trilayer structures [52,53] and nonlocal transport experiments in Pt/YIG bilayer nanostructures [54][55][56].…”

Spin Hall magnetoresistance in antiferromagnetic insulators

“…This effect is denoted as spin Hall magnetoresistance (SMR). [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] It is based on an interfacial exchange of angular momentum from the sublattice magnetizations to the conduction electrons of the heavy metal and has to be distinguished from a static spin polarization due to magnetic proximity effects. [44][45][46] 2.1.…”