Novel torque magnetometry for uniaxial anisotropy constants of thin films and its application to FePt granular thin films

Abstract

A technique based on torque magnetometry is proposed for precise determination of the uniaxial magnetic anisotropy constant, Ku, of perpendicularly magnetized thin films, in particular for Ku larger than 106 J/m3, by electrical detection of the anomalous Hall effect and exact determination of the magnetic field direction. This technique can measure the Ku value of several-nanometer-thick polycrystalline films. Further, the Ku value of FePt–C granular films, which are expected to be useful for high-density magnetic recording media, is evaluated. The intrinsic Ku value of 4-nm-thick FePt–C thin films fabricated at 450 °C is approximately 3 MJ/m3 for carbon contents up to 34 vol % C.

Contributions of magnetic structure and nitrogen to perpendicular magnetocrystalline anisotropy in antiperovskite ɛ−Mn4N

“…Magnetic anisotropy was measured via torque magnetometry based on the angle-dependent anomalous Hall effect (AHE). 26 In the theoretical calculation of Ku, we carried out first-principles density-functional calculations with the aid of the Vienna ab initio simulation program (VASP), 27,28 where lattice constants estimated from the in-plane and out-of-plane XRD profiles were used. Prior to the estimation of Ku, we first calculated the formation energy of Mn4N (Etotal) assuming two types of collinear ferrimagnetic structures.…”

“…Figure 2(c) shows a representative saturated magnetic torque curve based on measurement of the AHE. 26 By fitting the curve with T = -(Ku1 + Ku2)sin2θM + (Ku2/2)sin4θM, the first-and second-order uniaxial magnetic anisotropy constants Ku1 and Ku2 were obtained, where θM denotes the magnetization angle with respect to the film plane normal, given by θM = arccos[RAHE(H) / RAHE]. The resultant Ku values were found to be dominated by Ku1 (the Ku2 contribution can be neglected), and the peak value was comparable to that of Mn4N fabricated using MBE 19 and pulsed laser deposition.…”

Recent advances in SmFe12-based permanent magnets

“…Ogawa et al measured the temperature dependence of the first- and second-order uniaxial magnetic anisotropy constants, K 1 and K 2 , of the Sm(Fe 1-x Co x ) 12 film, as shown in Figure 4 [ 31 ]. K 1 and K 2 were estimated using the AHE-torque method [ 39 ]. The theoretically calculated results are shown in the same figure.…”

Magnetocrystalline anisotropy and volume ratio of FePt grains with c-axes parallel to the film plane in FePt granular film with various grain boundary materials

“…[1][2][3][4][5] Although it has been reported that there existed FePt grains whose c-axes are parallel to the film plane (inplane grains) with FePt grains whose c-axes are normal to the film plane (normal grains) in a FePt granular film with grain boundary material (GBM), [6][7][8] a dominant factor affecting the c-axis orientation for FePt grains with cubic (disorder), tetragonal (order) system which is slightly distorted along the film normal direction, and/or twin was not clarified yet in FePt granular film with various GBMs. And there have been some reports about K u⊥ averaged over the full FePt granular layer and magnetocrystalline anisotropy (K u grain ), [9][10][11][12] the effect of in-plane grains on these magnetic properties was not received significant attention and not clear. Therefore, we evaluated the volume ratio of in-plane grains to normal grains (R parallel ) in the FePt granular films with various GBMs (GBMs: B 2 O 3 , SnO, WO 3 , Nb 2 O 5 , TiO 2 , MnO, MgO, and C).…”