Spin Seebeck effect through antiferromagnetic NiO

Abstract

We report temperature-dependent spin-Seebeck measurements on Pt/YIG bilayers and Pt/NiO/YIG trilayers, where YIG (Yttrium iron garnet, Y 3 Fe 5 O 12 ) is an insulating ferrimagnet and NiO is an antiferromagnet at low temperatures. The thickness of the NiO layer is varied from 0 to 10 nm. In the Pt/YIG bilayers, the temperature gradient applied to the YIG stimulates dynamic spin injection into the Pt, which generates an inverse spin Hall voltage in the Pt. The presence of a NiO layer dampens the spin injection exponentially with a decay length of 2±0.6 nm at 180 K. The decay length increases with temperature and shows a maximum of 5.5±0.8 nm at 360 K. The temperature dependence of the amplitude of the spin-Seebeck signal without NiO shows a broad maximum of 6.5±0.5 μV/K at 20 K. In the presence of NiO, the maximum shifts sharply to higher temperatures, likely correlated to the increase in decay length. This implies that NiO is most transparent to magnon propagation near the paramagnet-antiferromagnet transition. We do not see the enhancement in spin current driven into Pt reported in other papers when 1-2 nm NiO layers are sandwiched between Pt and YIG.

Influence of Thickness and Interface on the Low-Temperature Enhancement of the Spin Seebeck Effect in YIG Films

“…Additionally, the theories of Diniz and Costa [51] and Cornelissen et al [52] have recently reproduced our temperature and thickness dependence of the LSSE results, corroborating our experiments and extending the explanation of our observations. Moreover, we note that Prakash et al [53] have shown interface and bulk effects in the spin Seebeck effect by inserting an antiferromagnetic NiO layer between the Pt and YIG. They argue that a thin NiO layer leads to a different temperature dependence of spin Seebeck signals, which is in a good agreement with our results.…”

Spin glass transition in a thin-film NiO/permalloy bilayer

“…They have recently attracted a renewed attention thanks to the high dynamical magnetization frequencies of AFs, enabling applications in fast interconversion and transmission of spin signals [3], and THz optics [4]. Additionally, vanishing magnetization of AFs can enable enhanced spin-transfer efficiency in electronic manipulation of the magnetic states for ultrahigh-density information storage, avoiding the constraints imposed by the angular momentum conservation and the dipolar fields ubiquitous to ferromagnetic systems [5].A number of novel phenomena have been recently observed or predicted for thin AF films, including antiferromagnetic spin-orbit torques [6][7][8], AF magnetoresistance [9], enhanced interconversion between electron spin current and spin waves [3,10], generation of THz signals [4,11], AF exchange springs [12,13], and topological effects [14][15][16]. While some of these phenomena are expected even for standalone AFs, strong exchange coupling at AF/F interfaces provides one of the most efficient approaches to controlling and analyzing the magnetization states of AFs, with the state of F controlled by the magnetic field or spin current, and characterized by the magnetoelectronic or optical techniques.…”

“…A 10-nm-thick Ni 80 Fe 20 =Permalloy (Py) ferromagnet and a 3 nmthick capping SiO 2 layer were deposited on top. NiO has played a prominent role in recent studies of magnetic, magnetoelectronic, and optical phenomena in AFs, thanks to its simple electronic, magnetic, and crystalline structure [3,4,10,12,17]. Additionally, the magnetocrystalline anisotropy of NiO is more than an order of magnitude smaller than that of other common AF such as CoO or Fe 50 Mn 50 [18], making NiO promising for the manipulation of its magnetization.…”

“…The demonstrated new type of spin glass may provide insight into the general mechanisms underlying the formation of ferroic glasses [39]. For the applications of NiO and other ultrathin AF films in spin-charge conversion and magnonic (spin wave-based) structures [3,5,10,14], we expect a transition at T B between two different regimes of spin wave propagation, and a large difference between the spin wave characteristics in the multidomain state of thick AF films and the spin-glass state of thin films. Surprisingly, a recent study suggests that spin disorder may result in enhanced spin-wave propagation [40].…”

Enhanced Spin Conductance of a Thin-Film Insulating Antiferromagnet

“…(See third section of the Supplemental Material [17].) In addition to MnF 2 , other materials, such NiO [20] and Cr 2 O 3 [1,21], are also possible candidates for the insulating antiferromagnetic layer.…”