Characterization of interlayer interactions in magnetic random access memory layer stacks using ferromagnetic resonance

Abstract

Ferromagnetic resonance spectroscopy is used to determine magnetic interactions in layer stacks designed for orthogonal spin-transfer magnetic random memory devices. The stacks have layers with different anisotropy directions and coupling, consisting of a perpendicularly magnetized polarizer, an in-plane magnetized free layer, and an in-plane magnetized exchange biased synthetic antiferromagnetic layer. The oscillatory exchange coupling strength in the synthetic antiferromagnet was measured along with its exchange bias. The free layer properties were also determined. It is demonstrated that this one integrated measurement technique is able to provide quantitative measurements of key magnetic parameters in a complex layer stack, which is a prerequisite for high turn-around device materials characterization and optimization.Orthogonal spin-transfer magnetic random access memory (OST-MRAM) devices offer fast (sub-ns) write performance and low power operation, of great interest for non-volatile memory applications. 1-3 They consist of a spinpolarizing layer with perpendicular magnetization (P) and a magnetic tunnel junction (MTJ) or spin valve with in-plane magnetization orientation of the electrodes (see Fig. 1(a)). One of the electrodes of the MTJ, the reference layer (RL), may be a part of a synthetic antiferromagnet (SAF). Large spin-transfer torques and fast switching have been predicted 1 and MTJ based prototype devices have recently been demonstrated. 3 These results were confirmed in measurements on similar devices in Ref. 4.Understanding and engineering the magnetic properties as well as the interactions between the magnetic layers plays a key role in optimizing their switching behavior and the magnetic stability of devices. Static measurement techniques such as vibrating sample magnetometry (VSM) turn out to be difficult to interpret due to the contributions of each layer to the hysteresis loops. A variety of techniques is used instead. Exchange coupling has been studied using magnetoresistance measurements, 5 Kerr microscopy, 6 and ferromagnetic resonance (FMR), 7 among many other methods. Exchange bias has been investigated in antiferromagnetic/ferromagnetic bilayers 8 or in synthetic antiferromagnets 7 using FMR. Furthermore, FMR is commonly applied for the determination of anisotropies of magnetic thin films. 9 Here we present a method for the full characterization of complex layer stacks based on FMR, specifically layer stacks designed for OST-MRAM devices. First, the FMR peaks are related to each of the in-plane ferromagnetic layers. Interlayer interactions modify the FMR resonance condition.A simple model is shown to describe the frequency dependence of all the observed in-plane resonance peaks and enables the determination of the layer magnetic anisotropies and interlayer interactions.The layer stacks were grown on oxidized silicon wafers using a Singulus TIMARIS physical vapor deposition module. One layer, the polarizer (P), has a high spinpolarization, coercivity and a perpendicular anisotropy (se...

Thickness-dependent resonance frequency of non-uniform procession mode in CoZr stripe-domain magnetic films

“…Ferromagnetic resonance is one of the most powerful tools [1][2][3][4][5][6][7], which has been widely used to study the dynamic magnetic properties of magnetic materials and multifarious devices [3,8,9], such as orthogonal spin-transfer magnetic random-access memories [8,10], magnetic sensors [11], exchange-coupled bilayer or multilayer structures [3,[12][13][14][15] and so on. Commonly, the magnetization precessions in magn etic materials are in-phase (namely the acoustic mode) in the low-frequency regions [6,11], which is already familiar to researchers.…”

Ferromagnetic Resonance

“…Magneto-optic (Paz, 2012), dipolar energy contributions (Bose, 2012), nanocrystalline (Maklakov, 2012;Raita, 2012), La0.7Sr0.3MnO3 films (Golosovsky, 2012), La0.67Ba0.33Mn1-yA y O3, A -Fe, Cr , voltage-controlled magnetic anisotropy (VCMA) and spin transfer torque (Zhu, 2012) and the typical properties of the inertial resonance are investigated (Olive, 2012). The exchange bias (Backes, 2012), Q cavities for magnetic material (Beguhn, 2012), MgO/CoFeB/Ta structure , the interfacial origin of the giant magnetoresistive effect (GMR) phenomenon (Prieto, 2012), selfdemagnetization field (Hinata, 2012), Fe3O4/InAs(100) hybrid spintronic structures (Huang, 2012), granular films (Kakazei, 1999(Kakazei, , 2001Sarmiento, 2007;Krone, 2011;Kobayashi, 2012), nano-sized powdered barium (BaFe12O19) and strontium (Sr Fe12O19) hexaferrites (Korolev, 2012), Ni0.7Mn0.3-x CoxFe2O4 ferrites (NiMnCo: x = 0.00, 0.04, 0.06, and 0.10) (Lee, 2012), thin films (Demokritov, 1996(Demokritov, ,1997Nakai, 2002;Lindner, 2004;Aswal, 2005;Jalali-Roudsar, 2005;Cochran, 2006;Mizukami, 2007;Seemann, 2010), Ni2MnGa films (Huang, 2004), magnetic/electronic order of films (Shames, 2012), Fe1-xGd(Tb)x films , in ε-Al0.06Fe1.94O3 (Yoshikiyo, 2012). 10 nm thick Fe/GaAs(110) film (Römer, 2012), triangular shaped permalloy rings (Ding, 2012) and Co2-Y hexagonal ferrite single rod (Bai, 2012) structures and properties have been studied by FMR tecniques (Spaldin, 2010).…”

Critical switching curves of FeCoB synthetic antiferromagnets

“…Further, the microwave proper ties of SAF have been well investigated through ferromagn etic resonance (FMR) spectroscopy to characterize a number of features including linewidth, absorption position, coupling strength, intensity, angle and temperaturedepend ence of resonant absorption, and manipulation of resonant modes [24][25][26][27][28][29][30][31]. Devices utilizing SAF as a component have also been investigated through FMR to study the different aniso tropies among device layers [32]. A dynamic generalization of static CC for SAF structures was theoretically proposed in [33] for SAF elements subjected to pulsed magnetic fields, showing the possibility of the reduction of the switching field amplitude by varying the pulse shape and length.…”