Anomalous Hall effect in epitaxialL10-Mn1.5Ga films with variable chemical ordering

Abstract

Abstract： The transport behaviors of weak localization and anomalous Hall effect (AHE) in perpendicularly magnetized L1 0 -Mn 1.5 Ga single-crystalline films are investigated as a function of degree of long-range chemical ordering and temperature. We observed significant weak localization and metal-insulator transition in highly disordered films. Our results provide new evidence that weak localization, phonons and magnons have negligibly smaller effect on extrinsic AHE resistivity than static defects for all the chemical disordered films, the overlook of which in conventional scaling laws may result in significant discrepancies and exponent n beyond 2 when fitting the data. Chemical disorder is found to exhibit strong tailoring effect on both intrinsic and extrinsic σ AH . Our results clarify the role of weak localization, phonons and magnons in AHE and offer a technological engineering approach of the AHE by altering long-range chemical ordering parameter of magnetic materials. Key words：Weak localization, Anomalous Hall effect, Chemical disorder, Perpendicular magnetic anisotropy, PACS: 72.15. Rn, 81.30.Hd, 75.30.Gw a) Author to whom correspondence should be addressed; Electronic mail: jhzhao@red.semi.ac.cnThe anomalous Hall effect (AHE) has attracted much attention due to both the fascinating underlying physics and the great application potential in sensors, memories and logics. [1][2][3][4][5][6][7][8] It is widely accepted that there are three mechanisms responsible for the AHE. The intrinsic AHE arises from the transverse velocity of the Bloch electrons induced by SOI and interband mixing, 9 as experimentally evidenced by quantum anomalous Hall effect. 10 The extrinsic mechanisms of skew scattering and side jump result from the impurity scattering of conduction electrons due to SOI. 11,12 Skew scattering yields a scaling relation between longitudinal resistivity ρ xx (conductivity σ xx =1/ρ xx ) and anomalous Hall resistivity ρ AH (conductivity σ AH ≈ρ AH /ρ xx 2 ) as ρ AH~ρxx , while other two mechanisms give ρ AH~ρxx 2 . Accordingly, scaling laws ρ AH~ρxx n and ρ AH =aρ xx +bρ xx 2 are conventionally used to describe the experimental data.In spite of the extensive studies, a unified scaling of AHE has remained a shortage. In stark contrast to present AHE theories, the exponent n was experimentally observed to be below 1 or beyond 2 in a variety of ferromagnets, e.g. 0.4 in hopping transport-accompanied Fe 3 O 4 films, 13 2.7 (2.85) in (111)-orientated Mn 2.03 Ga (Mn 1.38 Ga) films, 14 2.6 in Fe/Cr multilayers 15 and 3.7 in Co-Ag granular films. 16 Electron localization was recently found to yield a scaling with n=0 in chemically disordered FePt ultrathin films. 17 Noticeably, recent studies in Fe films revealed a negligible contribution of phonon skew scattering and a scaling ρ AH =a 0 ρ xx0 +bρ xx 2 , where a 0 ρ xx0 = α 0 ρ xx0 +βρ xx0 2 is the extrinsic contributions of skew scattering and side jump from static defects. 3 These intriguing observations make the scaling of AHE open questions. On the o...

Anomalous resistivity upturn in epitaxial L21-Co2MnAl films

“…Therefore, it is of extreme importance to control the low- T transport behaviors for a better SV performance, for instance, via taking advantage of the structural disorder effects of Co 2 MnAl films. Structural disorder such as impurities, strain, and dislocations in Mn-based alloys has been proved to account for the large variations in magnetooptical Kerr effects1516, Gilbert damping17, magnetic anisotropy18, anomalous Hall effect19, and for the occurrence of electronic disorder physics (e.g. weak localization20 and atomic tunneling effects212223).…”

Anomalous Hall effect inL10−MnAlfilms with controllable orbital two-channel Kondo effect

“…In common magnetic metals, e.g. Fe and L10-Mn1.5Ga [7,10], ρAH are always observed to decrease monotonically as T decreases. In striking contrast, ρAH of our L10-MnAl films shows non-monotonic T dependence.…”

“…Notably, in contrast to the conventional picture that ρAH scales with the total resistivity irrespective of its sources [3], recent experimental studies have revealed that both ρAH and the scaling relation are qualitatively different for various types of electron scattering. Phonon scattering was found to have no distinguishable contribution to extrinsic part of ρAH in ferromagnetic Fe, Co, Ni, L10-Mn1.5Ga films, Co/Pt multilayers, and paramagnetic Ni34Cu66 films [7][8][9][10][11][12]. When ρxx is dominated by phonon and static defect scattering, the AHE has a scaling of ρAH = a0 ρxx0+bρxx 2 , where ρxx0 is the residual resistivity, a0ρxx0 is the extrinsic contribution from both side jump and skew scattering, and b is the intrinsic anomalous Hall conductivity (AHC).…”

“…The strong Ts dependence of intrinsic AHC b should be attributed partly to the different T dependence of M (see Fig. 3(a)) and partly to the modification of Fermi surface by structural disorders (especially the chemical disorder) [10,13]. As shown in Fig.…”

The anomalous Hall effect in epitaxial Fe(110) films grown on GaAs(110)

“…In the work of Fe(001) thin films [20], the parameter b referring to intrinsic contribution was proved to be thickness independent, which agreed with the intrinsic values measured in Fe whiskers [26] and calculated for Fe(001) perfect crystal [27]. The validity of this scaling was fully tested in thin films of Fe [20,21], Co [23], Ni [28], amorphous CoFeB [29], and chemical-ordered MnGa [30] and was justified by theoretical work [24]. At low temperatures, the resistivity q xx and the anomalous Hall resistivity q ah change slowly with temperature and thus approximately equal to q xx0 and q ah0 .…”