Fundamental magnetotransport anisotropy inR2Fe17single crystals

Abstract

We have measured the resistivity and Hall effect of R 2 Fe 17 (R = Y, Tb, and Gd) single crystals in the temperature T range 4 < T < 300 K and applied magnetic fields of up to 9 T. The anomalous Hall effect (AHE) is very anisotropic in these ferromagnets. The AHE resistivity, measured with an applied magnetic field H perpendicular to the c axis, is very large and varies quite linearly with the longitudinal resistivity ρ, but the AHE resistivity for H along the hard magnetization direction (H c axis) is much smaller and increases as ρ 2 . We argue that the latter is of the intrinsic origin and is brought about by quasidegenerate Fe d levels near the Fermi level.

Anisotropy of spin relaxation and transverse transport in metals

“…A second phenomenon, for which multiple experimental studies of anisotropy exist [18,19,20,21,22,23,24,25], but no quantitative theoretical argumentation for its emergence had been presented until recently [17], is the anomalous Hall effect [36,37,38]. The essence of the AHE in a ferromagnet lies in the generation of a charge current J H transverse to the electric : an electron with a certain direction of spin, injected into a solid which exhibits anisotropic spin-relaxation will lose the memory of its initial spin polarization over a period of time, which depends on the direction of the spin-polarization in real space (z or x, red and blue arrows correspondingly).…”

“…Experimentally, the − sometimes strong − anisotropy of the anomalous Hall effect in metals is a rather well-known phenomenon: see, e.g., experimental data for bcc Fe [18], fcc Ni [19,20], hcp Gd [21], as well as FeCr 2 S 4 [22], Yb 14 MnSb 11 [23], Y 2 Fe 17−x Co x [24] and R 2 Fe 17 (R = Y, Tb, Gd) [25]. Theoretically, the first argumentation for a strongly anisotropic behavior of the AHC in transition metals was provided by Roman et al [17].…”

“…Since such anisotropy is an intrinsic property of the crystalline solid, it should be properly averaged when using polycrystalline samples, as well as when considering the effect of temperature and magnetization dynamics on the measured spin polarization or transverse current [17]. Experimentally, only the anisotropy of the anomalous Hall effect with respect to the direction of the magnetization in the sample has been researched in the past and in many cases a very large anisotropy was found [18][19][20][21][22][23][24][25], while evidence of anisotropy in the spin Hall effect [26] and spin relaxation has been presented only recently [27,28].…”

Anisotropic intrinsic anomalous Hall effect in ordered3dPt alloys

“…Although experimentally, anisotropic AHE has been observed in many materials, e.g. bcc Fe, 18 fcc Ni, 19,20 hcp Gd, 21 as well as FeCr 2 S 4 , 22 Yb 14 MnSb 11 , 23 Y 2 Fe 17−x Co x and R 2 Fe 17 (R = Y, Tb, Gd), 25 only two studies of the anisotropy of the AHE from first principles have been performed so far. Roman et al 14 considered the anisotropic AHE in uniaxial hcp Co, calculated the ratio of the AHCs for the out-of-plane and in-plane magnetization, σ z and σ x , respectively, and found it to be as large as four, which is close to the experimentally ob-served ratio.…”

“…14,16,17 In the case of the AHE, the presence of the magnetization M in a ferromagnet leads to a strong dependence of the components of the conductivity tensor on the magnetization direction in the sample. Although experimentally, anisotropic AHE has been observed in many materials, e.g., bcc Fe, 18 fcc Ni, 19,20 hcp Gd, 21 24 and R 2 Fe 17 (R = Y, Tb, Gd), 25 only two studies of the anisotropy of the AHE from first principles have been performed so far. Roman et al 14 considered the anisotropic AHE in uniaxial hcp Co, calculated the ratio of the AHCs for the out-of-plane and in-plane magnetization, σ z and σ x , respectively, and found it to be as large as four, which is close to the experimentally observed ratio.…”