Electrically detected ferromagnetic resonance

Abstract

We study the magnetoresistance properties of thin ferromagnetic CrO 2 and Fe 3 O 4 films under microwave irradiation. Both the sheet resistance and the Hall voltage V Hall characteristically change when a ferromagnetic resonance ͑FMR͒ occurs in the film. The electrically detected ferromagnetic resonance ͑EDFMR͒ signals closely match the conventional FMR, measured simultaneously, in both resonance fields and line shapes. The sign and the magnitude of the resonant changes ⌬ / and ⌬V Hall / V Hall can be consistently described in terms of a Joule heating effect. Bolometric EDFMR thus is a powerful tool for the investigation of magnetic anisotropy and magnetoresistive phenomena in ferromagnetic micro-or nanostructures. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2722027͔The occurrence of ferromagnetic resonance ͑FMR͒ affects the quasistatic properties of a magnetic material, such as its magnetoresistance, 1-4 magnetoimpedance, 5 or caloric properties. 6 These effects can be used to detect FMR in magnetic micro-and nanostructures. 4,6 This is attractive, as FMR is one of the most sensitive methods for the investigation of magnetic anisotropy. However, to exploit the potential of such novel FMR detection methods, their full equivalence with the well established conventional cavity-based FMR must first be demonstrated. In semiconductors, the effect of paramagnetic resonance on transport processes is well known. 7-9 Here, we report on nonresonant and resonant changes of the magnetoresistance of thin ferromagnetic CrO 2 and Fe 3 O 4 films upon microwave irradiation. We show that these electrically detected ferromagnetic resonance ͑ED-FMR͒ signals are spectroscopically equivalent to conventional FMR measured simultaneously, and that the sign and the magnitude of the EDFMR signals can be quantitatively understood in terms of a Joule heating effect. This opens the way to selectively investigate particular transport processes in ferromagnets via magnetic resonance techniques.The single-crystalline, 100 nm thick CrO 2 films studied were deposited on ͑100͒-oriented TiO 2 substrates by chemical vapor deposition. 10 After patterning them into 80 m wide and 600 m long Hall bar structures using optical lithography and wet chemical etching, we fabricated Ohmic contacts by depositing Au in situ immediately after sputter cleaning the film surface in an Ar plasma. 11 The magnetite ͑Fe 3 O 4 ͒ samples were grown on ͑100͒-oriented MgO substrates by pulsed laser deposition. 12 Here, we study a 32 nm thick, coherently strained Fe 3 O 4 film with Ohmic contacts in van der Pauw geometry, realized by wedge bonding Al wires.The FMR spectra were measured in an X-band ͑9 GHz͒ electron spin resonance setup at room temperature as a function of a static magnetic field H, using magnetic field modulation at 100 kHz with an amplitude 0 ⌬H = 3.2 mT. Simultaneously to the FMR, we recorded the longitudinal magnetoresistance or the Hall effect in the samples in fourpoint geometry, with ac current bias I at a frequency I ഛ 1.1 kHz. The magnetiza...

Bolometric Detection of Ferromagnetic Resonance in Amorphous Microwires

“…7. For the CoFeCrSiB wire, this dependence can be approximately described by the square root function of P in , (the dashed curve) which is in agreement with the results of [11]. The (P in ) 1/2 dependence of the proportionality constant c can be explained by the linear characteristic of the microwave diode, which is relevant for microwave powers of the order of few 10 mW.…”

“…Many different mechanisms can contribute to the modification of electric properties at the FMR, such as anisotropic magnetoresistance (AMR) [3], [4], Hall effect [3], spin pumping [5], spin-transfer torque [6]- [8] bolometric effect [9], and others. To distinguish between different contributions to ED-FMR, some experimental methods have been proposed [10], [11]. In this paper, we report on the investigation of ED-FMR in glass-coated amorphous microwires at X-band microwave frequency.…”

Increase in temperature of a ferromagnetic substance in rf magnetic field

“…The investigation of ferromagnetic resonance with possible applications in nanoparticles has been demonstrated by Walton et al [6]. Goennenwein et al estimated the change in electrical properties of ferromagnetic materials due to ferromagnetic resonance [7]. Sakran et al demonstrated the localized heating of magnetite nanoparticles via ferromagnetic resonance and reported the rise in temperature [8].…”

Dynamic magnetic susceptibility and electrical detection of ferromagnetic resonance

“…The peak position and peak width can be used to determine magnetic anisotropy and the Gilbert damping coefficient 7,8 . In recent years, the electrical detection of FMR, in which a dc-voltage is measured on a sample around FMR, becomes very popular due to the high accuracy of dc-voltage measurements and only microns sample size needed [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] . This technique has been used by many groups [11][12][13][14][15][16][17] in recent years to extract spin pumping and the spin Hall angle that measures the strength of both the spin Hall effect (SHE) and the inverse spin Hall effect (ISHE).…”