C.J. Oates

High field ferromagnetic resonance measurements of the anisotropy field of longitudinal recording thin-film media

The average value of the magnetocrystalline anisotropy field, Hk, is an important parameter for the characterization of magnetic recording media but is difficult to measure accurately due in part to the effect of interactions between the grains. In order to evaluate Hk we have studied two model CoCrPtTa magnetic films using a number of complementary techniques: high field ferromagnetic resonance (FMR) (35.0–45.0 kOe), low field (<20 kOe) vector vibrating-sample magnetometry and torque magnetometry. The FMR measurements were performed at a number of discrete frequencies in the range 75–93 GHz using a new quasi-optical spectrometer developed at the University of St. Andrews. The values of Hk derived by FMR (10.8 kOe) are approximately 10% greater than those obtained from conventional magnetometry (9.6 kOe). This difference is believed to be due to the presence of intergranular exchange coupling which reduces the measured value of anisotropy when the applied field is not sufficiently large to completely alig...

Ferromagnetic resonance experiments in an obliquely deposited FeCo–Al2O3 film system

Granular cermet films (Fe50Co50)x–(Al2O3)1−x fabricated using the electron-beam coevaporation technique at oblique incidence of FeCo and alumina atom fluxes have been found to exhibit both oblique and in-plane uniaxial magnetic anisotropy. This anisotropy first appears just below the percolation threshold due to a magnetic coupling of particles taking place at a certain stage of their growth and coalescence. The FeCo content x varied from 0.07 to 0.49. A simple model of the film microstructure is presented based on the results of magnetization measurements and ferromagnetic resonance at intermediate (9.4 GHz) and high (94 GHz) frequencies. At 94 GHz the concentration dependence of the effective anisotropy field follows the solid solution law, since then the magnetic field is sufficient to magnetize the films close to saturation. The 9.4 GHz data points deviate from the solid solution line below the percolation threshold due to both modification of the resonance fields by intergranular interactions in nons...

Torque magnetometry: investigation of the intergranular exchange interaction in longitudinal magnetic recording media

Abstract We demonstrate a new method for investigation of intergranular exchange coupling in longitudinal magnetic recording media by means of torque magnetometry. The technique we use is based on an analogy with the Δ M method where the analysis involves comparison of reversal processes in the sample with different initial magnetic states. We show that the Δ M curve has an equivalent torque representation Δ τ which can be similarly exploited for studies on the longitudinal media. To validate the method we involve micromagnetic modeling, results of which are compared with the experimental measurements on a model CoCrPtTa media sample.

Neutron Studies of Magnetic Recording Media

Small-angle neutron studies have been performed on samples of continuous inhomogeneous magnetic recording media. This has allowed the local magnetic structure to be probed at a subnanometre resolution, revealing some interesting information about the size and shape of the magnetic grains and their relation to the physical grains.

Agglomeration effects in FePt nanoparticles on Si substrates studied by small angle neutron scattering and magnetometry

In this paper, we investigate particle sizes and magnetic properties of FePt nanoparticles to determine if annealing at high temperatures for short times leads to the desired magnetic properties with reduced agglomeration. We used small angle neutron scattering and vibrating sample magnetometry for investigation.

High-Field FMR Investigation of Epitaxially Grown Fe4 N Films on a MgO(001) Substrate

Epitaxially grown Fe 4 N thin film on a MgO(001) substrate has been examined by high-field ferromagnetic resonance (FMR) spectroscopy. When the magnetic field was applied parallel (along the in-plane direction) and perpendicular to the substrate, the resonance appeared at 2.4 and 4.9 T at 94 GHz, respectively. The g-value and the effective magnetization were estimated to be 2.13 and 191 emu g - 1 , respectively, using the relation derived from the Landau-Lifshitz equation of motion. Superconducting quantum interference device (SQUID) measurements also showed that the Fe 4 N epitaxial film has a large magnetization anisotropy, supporting that the magnetic moments lie along the in-plane direction.