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A novel approach to tune the ferromagnetic resonance frequency of a soft magnetic Ni 80 Fe 20 (Permalloy = Py) film with in-plane magnetic anisotropy (IMA) based on the controlled coupling to a hard magnetic NdCo x film with perpendicular magnetic anisotropy (PMA) through a non-magnetic Al spacer is studied. Using transverse magneto-optical Kerr effect (TMOKE), alternating gradient magnetometry (AGM) as well as vector network analyzer ferromagnetic resonance (VNA-FMR) spectroscopy, the influence of both Co concentration and Al spacer thickness on the static and dynamic magnetic properties of the coupled IMA/PMA system is investigated. Compared to a single Py film, two striking effects of the coupling between IMA and PMA layers can be observed in their FMR spectra. First, there is a significant increase in the zero-field resonance frequency from 1.3 GHz up to 6.6 GHz, and second, an additional frequency hysteresis occurs at low magnetic fields applied along the hard axis. The maximum frequency difference between the frequency branches for increasing and decreasing magnetic field is as high as 1 GHz, corresponding to a tunability of about 20% at external fields of typically less than ±70 mT. The origin of the observed features in the FMR spectra is discussed by means of magnetization reversal curves.The magnetic properties of thin films and multilayers exhibiting stripe domains have been investigated extensively in both experiment and theory since their discovery more than half a century ago 1 . In recent years, research results on stripe domains have triggered the prospect of employing their unique properties in future microwave, magnonic, and spintronic devices with novel functionalities. The formation of stripe domains is the result of energy minimization as well as the competition between PMA (K ⊥ ) and shape anisotropy ( 1 2 µ 0 M 2 S ), which favor out-of-plane and in-plane magnetization, respectively. The ratio Q = 2K ⊥ /µ 0 M 2 S , known as reduced anisotropy or quality factor 2 , is commonly used to describe the extent of stripe domains. For moderate (Q < 1) to weak (Q 1) PMA, the magnetization tends to lie in the plane, but above a critical film thickness d cr , a ground state with stripe domains emerges. The latter is characterized by a perpendicular magnetization component alternating between up and down within a period λ . The critical thickness d cr is typically in the range of 20 -40 nm for moderate Q value materials such as amorphous NdCo alloys 3,4 , whereas for materials like Py with small values of Q, generally larger values of d cr = 170 -300 nm are found 5-8 . Intimately linked to the presence of stripe domains is the occurrence of a pseudo-uniaxial or rotatable anisotropy 9,10 , which is the result of the in-plane magnetization being aligned along the stripe direction. The latter, however, is not fixed as it can be reoriented by applya) Electronic