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論文

Fe contribution to the magnetic anisotropy of $$L1_0$$-ordered FePt thin films studied by angle-dependent X-ray magnetic circular dichroism

芝田 悟朗; 池田 啓祐*; 高梨 弘毅; 藤森 淳*; 他8名*

Applied Physics Letters, 127(14), p.142406_1 - 142406_6, 2025/10

https://doi.org/10.1063/5.0283193

We have investigated the contribution of the Fe $$3d$$ electrons to its magnetic anisotropy energy by angle-dependent X-ray magnetic circular dichroism at the Fe $$L_{2,3}$$ edge. By this technique, one can deduce the magnetic dipole moment $$m_T$$, which represents the anisotropic spatial distribution of spin-polarized electrons, and the orbital moment anisotropy (OMA) of Fe $$3d$$ electrons. Detected finite $$m_T$$ indicates that the spin-polarized Fe $$3d$$ electrons are distributed preferentially in the out-of-plane direction of the films. This $$m_T$$ of Fe overwhelms the positive contribution of OMA to PMA, and reduces the PMA of $$L1_0$$-ordered FePt thin films, consistent with a previous first-principles calculation. The present result implies that a large positive contribution of the non-magnetic element Pt rather than Fe governs the PMA of $$L1_0$$-ordered FePt thin films.

論文

Orbital magnetic moments in FeCr$$_2$$S$$_4$$ studied by X-ray magnetic circular dichroism

Verma, V. K.*; 芝田 悟朗; 藤森 淳*; 他8名*

Physical Review B, 112(10), p.104444_1 - 104444_8, 2025/09

https://doi.org/10.1103/hdzg-mn6r

We have investigated the element specific magnetic characteristics of single-crystal FeCr$$_{2}$$S$$_{4}$$ using X-ray magnetic circular dichroism (XMCD). We have found that the Fe L2,3-edge XAS spectra do not exhibit clear multiplet structures, indicating strong hybridization between the Fe 3d and S 3p orbitals, leading to delocalized rather than localized electronic states. The Fe 3d and Cr 3d spin moments are antiferromagnetically coupled, consistent with the Goodenough-Kanamori rule. The orbital magnetic moments of Fe and Cr are determined to be -0.23 and -0.017 $$mu$$B/ion, respectively. The large orbital magnetic moment of Fe is due to the d6 configuration under the relatively weak tetrahedra crystal field at the Fe site, and the delocalized Fe electrons maintain the orbital degree of freedom in spite of their itinerant nature. On the other hand, the octahedral crystal-field splitting of the Cr 3d level is large enough to result in the quenching of the orbital moment of the Cr ion in FeCr$$_{2}$$S$$_{4}$$.

論文

Hard X-ray photoemission study of bulk single-crystalline InGaZnO$$_4$$

芝田 悟朗; 他9名*

Applied Physics Letters, 126(24), p.241902_1 - 241902_6, 2025/06

https://doi.org/10.1063/5.0271655
 被引用回数：0 パーセンタイル：0.00(Physics, Applied)

We performed hard X-ray photoemission spectroscopy (HAXPES) experiments of bulk single-crystalline InGaZnO$$_4$$ (sc-IGZO), which was recently synthesized via the optical floating zone method, in order to reveal the bulk intrinsic electronic structure. We find that oxygen vacancies are preferentially located around In atoms in as-grown crystals, which are filled out by post-annealing in an oxygen atmosphere. The subgap states near the valence-band maximum (VBM) were much weaker than those in the previous study even without oxygen annealing, which suggests that the loss of crystallinity is relevant to the formation of them in addition to the oxygen vacancies.

論文

Spin-orbit-entangled state of Ba$$_2$$CaOsO$$_6$$ studied by O $$K$$-edge resonant inelastic X-ray scattering and Raman spectroscopy

岡本 淳*; 芝田 悟朗; 藤森 淳; 他9名*

npj Quantum Materials (Internet), 10, p.44_1 - 44_8, 2025/04

https://doi.org/10.1038/s41535-025-00757-4
 被引用回数：0 パーセンタイル：64.27(Materials Science, Multidisciplinary)

Transition-metal ions with 5$$d^2$$ electronic configuration in a cubic crystal field are prone to have a vanishing dipolar magnetic moment but finite higher-order multipolar moments, and they are expected to exhibit exotic physical properties. Through an investigation using resonant inelastic X-ray spectroscopy (RIXS), Raman spectroscopy, and theoretical ligand-field multiplet and ab initio calculations, we fully characterized the electronic structure of Ba$$_2$$CaOsO$$_6$$, particularly, the crystal field symmetry of the 5$$d^2$$ electrons in this anomalous material. The low-energy multiplet excitations from RIXS at the oxygen $$K$$ edge and Raman-active phonons both show no splitting, confirming the absence of Jahn-Teller distortion. These findings are consistent with the ground state with the "hidden order" of magnetic octupoles.

論文

Relationship between orbital moment anisotropy, magnetocrystalline anisotropy, and Dzyaloshinskii-Moriya interaction in W/Co/Pt trilayers

Chi, Z.*; 芝田 悟朗; 藤森 淳; 他15名*

Physical Review B, 110, p.184401_1 - 184401_8, 2024/11

https://doi.org/10.1103/PhysRevB.110.184401
 被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

We have studied the Co layer thickness dependences of magnetocrystalline anisotropy (MCA), Dzyaloshinskii-Moriya interaction (DMI), and orbital moment anisotropy (OMA) in W/Co/Pt trilayers, in order to clarify their correlations with each other. We find that the MCA favors magnetization along the film normal and monotonically increases with decreasing effective magnetic layer thickness ($$t_{rm eff}$$). The magnitude of the Dzyaloshinskii-Moriya exchange constant ($$|D|$$) increases with decreasing $$t_{rm eff}$$ until $$T_{rm eff}$$ $$sim$$ 1 nm, below which $$|D|$$ decreases. The MCA and $$|D|$$ scale with 1/$$T_{rm eff}$$ for $$t_{rm eff}$$ larger than $$sim 1$$ nm, indicating an interfacial origin. Using X-ray magnetic circular dichroism (XMCD), we find non-zero OMA when $$t_{rm eff}$$ is smaller than $$sim 0.8$$ nm. The OMA increases with decreasing $$t_{rm eff}$$ more rapidly than what is expected from the MCA, indicating that factors other than OMA contribute to the MCA at small $$t_{rm eff}$$.

論文

強磁性5$$d$$ $$j_{eff}=3/2$$絶縁体Sr$$_3$$OsO$$_6$$のX線磁気円二色性測定

若林 勇希*; Krockenberger, Y.*; 山神 光平*; 和達 大樹*; 芝田 悟朗; 藤森 淳*; 河村 直己*; 鈴木 基寛*; 谷保 芳孝*; 山本 秀樹*

SPring-8/SACLA利用研究成果集(インターネット), 12(5), p.291 - 293, 2024/10

https://doi.org/10.18957/rr.12.5.291

本研究では、高温強磁性酸化物Sr$$_3$$OsO$$_6$$の電子状態を明らかにすることを目的として、Os $$L_{2,3}$$吸収端におけるX線吸収分光(XAS)及びX線磁気円二色性(XMCD)測定を行った。実験結果から、Osの軌道磁気モーメントがスピン磁気モーメントと同程度のオーダーであることが明らかになった。しかし、XMCD総和則による推定では、軌道磁気モーメントはSQUID磁化測定の値よりもかなり小さかった。今後の課題としては、SrやOの吸収端でのXMCD測定による磁気モーメントの観測や、サンプルの経時変化を低減させるための対策が挙げられる。

論文

Origin of magnetically dead layers in spinel ferrites $$M$$Fe$$_2$$O$$_4$$ grown on Al$$_2$$O$$_3$$; Effects of postdeposition annealing studied by XMCD

野中 洋亮*; 若林 勇希*; 芝田 悟朗; 坂本 祥哉*; 池田 啓祐*; Chi, Z.*; Wan, Y.*; 鈴木 雅弘*; 田中 新*; 田中 雅明*; et al.

Physical Review Materials (Internet), 7(4), p.044413_1 - 044413_10, 2023/04

https://doi.org/10.1103/PhysRevMaterials.7.044413
 被引用回数：5 パーセンタイル：44.41(Materials Science, Multidisciplinary)

We study the electronic and magnetic states of as-grown and annealed $$M$$Fe$$_2$$O$$_4$$(111)/Al$$_2$$O3(111) ($$M =$$Co, Ni) thin films with various thicknesses grown on Si(111) substrates with the $$gamma$$-Al$$_2$$O$$_3$$(111)buffer layers by using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD), to investigate magnetically dead layers in these films. Although the magnetically dead layers in the as-grown samples are formed near the interface with the Al$$_2$$O$$_3$$ buffer layer, we reveal that ferrimagnetic order is partially recovered by postdeposition annealing at 973 K for 48 hours in air. By analyzing the line shapes of the XAS and XMCD spectra, we conclude that, in the dead layers, there are a significant number of vacancies at the $$T_d$$ sites of the spinel structure, which may be the microscopic origin of the degraded ferrimagnetic order in the $$M$$Fe$$_2$$O$$_4$$ thin films.

論文

垂直磁気異方性を示す鉄挿入遷移金属ダイカルコゲナイドFe$$_x$$TaS$$_2$$のX線磁気円二色性による研究; Fe$$_x$$TiS$$_2$$との比較

芝田 悟朗; Won, C.*; Kim, J.*; 野中 洋亮*; 池田 啓祐*; Wan, Y.*; 鈴木 雅弘*; 小出 常晴*; 田中 新*; Cheong, S.-W.*; et al.

Photon Factory Activity Report 2022 (インターネット), 2 Pages, 2023/00

https://pfwww.kek.jp/acr/2022pdf/u_reports.html

Feをインターカレートした遷移金属ダイカルコゲナイド化合物Fe$$_x$$TiS$$_2$$およびFe$$_x$$TaS$$_2$$は、巨大な保磁力および垂直磁気異方性を示す強磁性体になることが知られている。我々は以前、Fe$$_x$$TiS$$_2$$についてのX線磁気円二色性(XMCD)実験の結果から、Fe$$^{2+}$$の凍結していない軌道磁気モーメントが結晶場の1次摂動によって直接磁気異方性エネルギーを生むことを明らかにした。今回、Fe$$_x$$TiS$$_2$$よりもさらに強い磁気異方性を示す遷移金属ダイカルコゲナイドFe$$_x$$TaS$$_2$$について同様にXMCD実験を行い、磁気異方性の強さが何によって左右されているかを探ることを試みた。

論文

Cr doping-induced ferromagnetism in the spin-glass Cd$$_{1-x}$$Mn$$_x$$Te studied by X-ray magnetic circular dichroism

Verma, V.*; 坂本 祥哉*; 石川 弘一郎*; Singh, V. R.*; 石上 啓介*; 芝田 悟朗; 門野 利治*; 小出 常晴*; 黒田 真司*; 藤森 淳*

Physica B; Condensed Matter, 642, p.414129_1 - 414129_5, 2022/10

https://doi.org/10.1016/j.physb.2022.414129
 被引用回数：5 パーセンタイル：37.08(Physics, Condensed Matter)

The prototypical diluted magnetic semiconductor Cd$$_{1-x}$$Mn$$_x$$Te is a spin glass ($$x < 0.6$$) or an antiferromagnet ($$x > 0.6$$) but becomes ferromagnetic upon doping with a small amount of Cr atoms. To investigate the origin of the ferromagnetism in Cd$$_{1-x-y}$$Mn$$_x$$Cr$$_y$$Te, we have studied its element specific magnetic properties by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). Measured XAS and XMCD spectra indicate that both Cr and Mn atoms are divalent and that the magnetic moments of Cr and Mn are aligned parallel. By analyzing the element-specific magnetization curves, we conclude that Cr doping leads to the formation of ferromagnetic or superparamagnetic clusters consisting of several Cr ions surrounded by a much larger number of Mn ions.

論文

Magnetic properties and electronic configurations of Mn ions in the diluted magnetic semiconductor Ba$$_{1-x}$$K$$_x$$(Zn$$_{1-y}$$Mn$$_y$$)$$_2$$As$$_2$$ studied by X-ray magnetic circular dichroism and resonant inelastic X-ray scattering

鈴木 博人*; Zhao, G.*; 岡本 淳*; 坂本 祥哉*; Chen, Z.-Y.*; 野中 洋亮*; 芝田 悟朗; Zhao, K.*; Chen, B.*; Wu, W.-B.*; et al.

Journal of the Physical Society of Japan, 91(6), p.064710_1 - 064710_5, 2022/06

https://doi.org/10.7566/JPSJ.91.064710
 被引用回数：4 パーセンタイル：42.37(Physics, Multidisciplinary)

The magnetic properties and the electronic excitations of the new diluted magnetic semiconductor Ba$$_{1-x}$$K$$_x$$(Zn$$_{1-y}$$Mn$$_y$$)$$_2$$As$$_2$$ have been studied by X-ray magnetic circular dichroism (XMCD) and resonant inelastic X-ray scattering (RIXS). The sum rule analysis of the XMCD spectra indicates that the Mn atoms are in the high-spin configurations of $$d^5$$, whereas the presence of competing ferromagnetic and antiferromagnetic interactions between the Mn ions reduces the net spin moment. Based on a comparison of the RIXS line shapes with those of Ga$$_{1-x}$$Mn$$_x$$As, it is concluded that the ground state of Mn in Ba$$_{1-x}$$K$$_x$$(Zn$$_{1-y}$$Mn$$_y$$)$$_2$$As$$_2$$ consists of both the $$3d^5 underline{L}$$ and $$3d^5$$ electron configurations.

論文

Alternation of magnetic anisotropy accompanied by metal-insulator transition in strained ultrathin manganite heterostructures

小林 正起*; Anh, L. D.*; 鈴木 雅弘*; 金田-高田 真悟*; 竹田 幸治; 藤森 伸一; 芝田 悟朗*; 田中 新*; 田中 雅明*; 大矢 忍*; et al.

Physical Review Applied (Internet), 15(6), p.064019_1 - 064019_10, 2021/06

https://doi.org/10.1103/PhysRevApplied.15.064019
 被引用回数：8 パーセンタイル：42.04(Physics, Applied)

A fundamental understanding of the interfacial magnetic properties in ferromagnetic heterostructures is essential for utilizing ferromagnetic materials for spintronic device applications. Here, we investigate the interfacial magnetic and electronic structures of epitaxial single-crystalline LaAlO$$_3$$(LAO)/La$$_{0.6}$$Sr$$_{0.4}$$MnO$$_3$$(LSMO)/Nb:SrTiO$$_3$$(Nb:STO) heterostructures with varying LSMO layer thicknesses, in which the magnetic anisotropy strongly changes with the LSMO thickness due to the delicate balance between strains originating from both the Nb:STO and LAO layers, using X-ray magnetic circular dichroism and photoemission spectroscopy. We successfully detect the clear change of the magnetic behavior of the Mn ions concomitant with the thickness-dependent metal-insulator transition. Our results suggest that the double-exchange interaction induces ferromagnetism in the metallic LSMO film under tensile strain caused by the STO substrate, while the superexchange interaction determines the magnetic behavior in the insulating LSMO film under compressive strain originating from the top LAO layer. The change in strain, depending on LSMO layer thickness, is confirmed by scanning transmission electron microscopy. Based on those findings, the formation of a magnetic dead layer near the LAO/LSMO interface is attributed to competition between the superexchange interaction via Mn $$3d_{3z^2-r^2}$$ orbitals under compressive strain and the double-exchange interaction via the $$3d_{x^2-y^2}$$ orbitals. These findings provide key aspects of ferromagnetic oxide heterostructures for the development of spintronic device applications.

論文

Electronic structure of the high-$$T_{rm C}$$ ferromagnetic semiconductor (Ga,Fe)Sb; X-ray magnetic circular dichroism and resonance photoemission spectroscopy studies

坂本 祥哉*; Tu, N. T.*; 竹田 幸治; 藤森 伸一; Hai, P. N.*; Anh, L. D.*; 若林 勇希*; 芝田 悟朗*; 堀尾 眞史*; 池田 啓祐*; et al.

Physical Review B, 100(3), p.035204_1 - 035204_8, 2019/07

https://doi.org/10.1103/PhysRevB.100.035204
 被引用回数：17 パーセンタイル：58.45(Materials Science, Multidisciplinary)

The electronic structure and the magnetism of the ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature $$T_{rm C}$$ can exceed room temperature, were investigated by means of X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic moments deduced using XMCD sum rules were found to be large, indicating that there is a considerable 3$$d^{6}$$ contribution to the ground state of Fe. From RPES, we observed a strong dispersive Auger peak and nondispersive resonantly enhanced peaks in the valence-band spectra. The latter is a fingerprint of the correlated nature of Fe 3$$d$$ electrons, whereas the former indicates their itinerant nature. It was also found that the Fe 3$$d$$ states have a finite contribution to the density of states at the Fermi energy. These states would be responsible for the ferromagnetic order in this material.

論文

Electronic structure of the high-$$T_{rm C}$$ ferromagnetic semiconductor (Ga,Fe)Sb; X-ray magnetic circular dichroism and resonance photoemission spectroscopy studies

坂本 祥哉*; Tu, N. T.*; 竹田 幸治; 藤森 伸一; Hai, P. N.*; Anh, L. D.*; 若林 勇希*; 芝田 悟朗*; 堀尾 眞史*; 池田 啓祐*; et al.

Physical Review B, 100(3), p.035204_1 - 035204_8, 2019/07

https://doi.org/10.1103/PhysRevB.100.035204

The electronic structure and the magnetism of the ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature $$T_{rm C}$$ can exceed room temperature, were investigated by means of X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic moments deduced using XMCD sum rules were found to be large, indicating that there is a considerable 3$$d^{6}$$ contribution to the ground state of Fe. From RPES, we observed a strong dispersive Auger peak and nondispersive resonantly enhanced peaks in the valence-band spectra. The latter is a fingerprint of the correlated nature of Fe 3$$d$$ electrons, whereas the former indicates their itinerant nature. It was also found that the Fe 3$$d$$ states have a finite contribution to the density of states at the Fermi energy. These states, presumably consisting of majority-spin $$p$$-$$d$$ hybridized states or minority-spin e states, would be responsible for the ferromagnetic order in this material.

論文

Local magnetic states of the weakly ferromagnetic iron-based superconductor Sr$$_{2}$$VFeAsO$$_{3-delta}$$ studied by X-ray magnetic circular dichroism

堀尾 眞史*; 竹田 幸治; 並木 宏允*; 片桐 隆雄*; 若林 勇希*; 坂本 祥哉*; 野中 洋亮*; 芝田 悟朗*; 池田 啓祐*; 斎藤 祐児; et al.

Journal of the Physical Society of Japan, 87(10), p.105001_1 - 105001_2, 2018/10

https://doi.org/10.7566/JPSJ.87.105001
 被引用回数：2 パーセンタイル：18.33(Physics, Multidisciplinary)

We have performed X-ray magnetic circular dichroism (XMCD) measurements on the iron-based superconductor Sr$$_{2}$$VFeAsO$$_{3-delta}$$ to study the origin of weak ferromagnetism (WFM) reported for this compound. While Fe 3d electrons show a magnetic response similar to the other iron pnictides, signals from V 3d electrons remain finite at zero magnetic field and may be responsible for the WFM.

論文

Cation distribution and magnetic properties in ultrathin (Ni$$_{1-x}$$Co$$_{x}$$)Fe$$_{2}$$O$$_{4}$$ (x=0-1) layers on Si(111) studied by soft X-ray magnetic circular dichroism

若林 勇希*; 野中 洋亮*; 竹田 幸治; 坂本 祥哉*; 池田 啓祐*; Chi, Z.*; 芝田 悟朗*; 田中 新*; 斎藤 祐児; 山上 浩志; et al.

Physical Review Materials (Internet), 2(10), p.104416_1 - 104416_12, 2018/10

https://doi.org/10.1103/PhysRevMaterials.2.104416
 被引用回数：15 パーセンタイル：45.42(Materials Science, Multidisciplinary)

We study the electronic structure and magnetic properties of epitaxial (Ni$$_{1-x}$$Co$$_{x}$$)Fe$$_{2}$$O$$_{4}$$(111) layers with thicknesses $$d$$ = 1.7 - 5.2 nm grown on Al$$_{2}$$O$$_{3}$$(111)/Si(111) structures. We revealed the crystallographic (octahedral $$O_{h}$$ or tetrahedral $$T_{d}$$) sites and the valences of the Fe, Co, and Ni cations using experimental soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectra and configuration-interaction cluster-model calculation.

論文

Origin of the large positive magnetoresistance of Ge$$_{1-x}$$Mn$$_{x}$$ granular thin films

若林 勇希*; 秋山 了太*; 竹田 幸治; 堀尾 眞史*; 芝田 悟朗*; 坂本 祥哉*; 伴 芳祐*; 斎藤 祐児; 山上 浩志; 藤森 淳*; et al.

Physical Review B, 95(1), p.014417_1 - 014417_6, 2017/01

https://doi.org/10.1103/PhysRevB.95.014417
 被引用回数：11 パーセンタイル：43.59(Materials Science, Multidisciplinary)

Ge$$_{1_x}$$Mn$$_x$$ (GeMn) granular thin films are a unique and promising material for spintronic applications owing to their large positive magnetoresistance (MR). The microscopic origin of the MR has not yet been clarified. Here, we develop a method to separately investigate the magnetic properties of the nanoparticles and the matrix, utilizing the extremely high sensitivity of X-ray magnetic circular dichroism (XMCD) to the local magnetic state of each atom. We find that the MR ratio is proportional to the product of the magnetizations originating from the nanoparticles and the matrix. This result indicates that the spin-polarized holes in the nanoparticles penetrate into the matrix and that these holes undergo first order magnetic scattering by the paramagnetic Mn atoms in the matrix, which induces the large MR.

論文

Magnetization process of the $$n$$-type ferromagnetic semiconductor (In,Fe)As:Be studied by X-ray magnetic circular dichroism

坂本 祥哉*; Anh, L. D.*; Hai, P. N.*; 芝田 悟朗*; 竹田 幸治; 小林 正起*; 高橋 文雄*; 小出 常晴*; 田中 雅明*; 藤森 淳*

Physical Review B, 93(3), p.035203_1 - 035203_6, 2016/01

AA2016-0502.pdf:1.1MB

https://doi.org/10.1103/PhysRevB.93.035203
 被引用回数：20 パーセンタイル：61.55(Materials Science, Multidisciplinary)

In order to investigate the mechanism of ferromagnetic ordering in the new $$n$$-type magnetic semiconductor (In,Fe)As codoped with Be, we have performed X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) studies. The spectral line shapes suggest that the ferromagnetism is intrinsic, originating from Fe atoms incorporated into the zinc-blende-type InAs lattice. The magnetization curves of Fe measured by XMCD were well reproduced by the superposition of a Langevin function representing superparamagnetic (SPM) behavior of nanoscale ferromagnetic domains and a $$T$$-linear function representing Curie-Weiss paramagnetism even much above the Curie temperatures. The data at 20 K showed a deviation from the Langevin behavior, suggesting a gradual establishment of macroscopic ferromagnetism on lowering temperature. The existence of nanoscale ferromagnetic domains indicated by the SPM behavior suggests spatial fluctuations of Fe concentration on the nanoscale.

論文

Thickness-dependent magnetic properties and strain-induced orbital magnetic moment in SrRuO$$_{3}$$ thin films

石上 啓介*; 吉松 公平*; 豊田 大介*; 滝沢 優*; 吉田 鉄平*; 芝田 悟朗*; 原野 貴幸*; 高橋 文雄*; 門野 利治*; Verma, V. K.*; et al.

Physical Review B, 92(6), p.064402_1 - 064402_5, 2015/08

https://doi.org/10.1103/PhysRevB.92.064402
 被引用回数：49 パーセンタイル：83.41(Materials Science, Multidisciplinary)

Thin films of the ferromagnetic metal SrRuO$$_{2}$$ (SRO) show a varying easy magnetization axis depending on the epitaxial strain, and undergo a metal-to-insulator transition with decreasing film thickness. We have investigated the magnetic properties of SRO thin films with varying thicknesses fabricated on SrTiO$$_{3}$$(001) substrates by soft X-ray magnetic circular dichroism at the Ru M2,3 edge. Results have shown that, with decreasing film thickness, the film changes from ferromagnetic to nonmagnetic at around 3 monolayer thickness, consistent with previous magnetization and magneto-optical Kerr effect measurements. The orbital magnetic moment perpendicular to the film was found to be 0.1$$mu$$B/Ru, and remained nearly unchanged with decreasing film thickness while the spin magnetic moment decreases. A mechanism for the formation of the orbital magnetic moment is discussed based on the electronic structure of the compressively strained SRO film.

論文

Orbital magnetic moment and coercivity of SiO$$_2$$-coated FePt nanoparticles studied by X-ray magnetic circular dichroism

高橋 文雄*; 門野 利治*; 山本 真平*; Singh, V. R.*; Verma, V.*; 石上 啓介*; 芝田 悟朗*; 原野 貴幸*; 竹田 幸治; 岡根 哲夫; et al.

Physical Review B, 90(2), p.024423_1 - 024423_5, 2014/07

AA2015-0417.pdf:0.45MB

https://doi.org/10.1103/PhysRevB.90.024423
 被引用回数：11 パーセンタイル：41.63(Materials Science, Multidisciplinary)

We have investigated the spin and orbital magnetic moments of Fe in FePt nanoparticles in the $$L1_{0}$$-ordered phase coated with SiO$$_2$$ by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements at the Fe $$L_{2,3}$$ absorption edges. The magnetic coercivity (H$$_{c}$$) was found to be as large as 1.8 T at room temperature, 3 times larger than the thin film value and 50 times larger than that of the gas phase condensed nanoparticles. The hysteresis curve is well explained by the Stoner-Wohlfarth model for noninteracting single-domain nanoparticles with the H$$_{c}$$ distributed from 1 to 5 T.

論文

Thickness-dependent ferromagnetic metal to paramagnetic insulator transition in La$$_{0.6}$$Sr$$_{0.4}$$MnO$$_3$$ thin films studied by X-ray magnetic circular dichroism

芝田 悟朗*; 吉松 公平*; 坂井 延寿*; Singh, V. R.*; Verma, V.*; 石上 啓介*; 原野 貴幸*; 門野 利治*; 竹田 幸治; 岡根 哲夫; et al.

Physical Review B, 89(23), p.235123_1 - 235123_5, 2014/06

AA2015-0419.pdf:0.33MB

https://doi.org/10.1103/PhysRevB.89.235123
 被引用回数：27 パーセンタイル：69.52(Materials Science, Multidisciplinary)

Metallic transition-metal oxides undergo a metal-to-insulator transition (MIT) as the film thickness decreases across a critical thickness of several monolayers (MLs), but its driving mechanism remains controversial. We have studied the thickness-dependent MIT of the ferromagnetic metal La$$_{0.6}$$Sr$$_{0.4}$$MnO$$_3$$ by X-ray absorption spectroscopy and X-ray magnetic circular dichroism. The results suggest that the ferromagnetic phase gradually and most likely inhomogeneously turns into the paramagnetic phase and both phases abruptly become insulating at the critical thickness.

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