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arXiv2026

Magnetic Anisotropy and Magnetization Dynamics in Si/Ni Multilayers Probed by FMR and VSM Magnetometry

The magnetic anisotropy and magnetization dynamics of sputtered [Si(40~Å)/Ni($t_{\mathrm{Ni}}$~Å)]$_{20}$ multilayers were systematically investigated at room temperature using SQUID--VSM magnetometry and angle-dependent ferromagnetic resonance (FMR). Static measurements reveal soft ferromagnetic behaviour in thicker Ni layers and mixed ferromagnetic and superparamagnetic contributions at reduced thicknesses. The saturation magnetization increases toward the bulk Ni value with increasing thickness, consistent with Ni nanocrystallite growth. Magnetic dead-layer analysis yields an interfacial dead-layer thickness of approximately $9$~Å per interface, accounting for the suppressed magnetization in thinner Ni layers. Angle-dependent FMR measurements reveal effective easy-plane magnetic anisotropy, while out-of-plane spectra exhibit additional non-uniform spin-wave modes. The effective magnetization remains lower than the static saturation magnetization, indicating a perpendicular anisotropy contribution that partially compensates the demagnetizing field. Quantitative anisotropy analysis yields an interfacial anisotropy constant of $K_S = +0.17~\mathrm{erg\,cm^{-2}}$, favouring perpendicular magnetization, and a volume anisotropy constant of $K_V = -1.23 \times 10^6~\mathrm{erg\,cm^{-3}}$, favouring in-plane alignment, with an extrapolated anisotropy crossover thickness of $t_c \approx 27$~Å. Increasing FMR line-shape asymmetry with decreasing Ni thickness is consistent with enhanced interfacial roughness. These findings highlight the competing interfacial and volume anisotropies and the importance of Ni thickness and interface quality in tailoring Si/Ni multilayers for silicon-compatible spintronic applications.

cond-mat.mes-hall↗

arXiv2026

Phonon evidence for a partial, re-entrant spin reorientation near room temperature in LaFe$_{1-x}$Ni$_x$O$_3$

Spin reorientation near room temperature offers a route to controlling antiferromagnetic order, yet LaFeO$3$, which lacks a magnetic rare-earth ion, is generally expected to retain its spin orientation along the $a$ axis below $T{\mathrm N}\approx740$~K. Here, we investigate LaFe$_{1-x}$Ni$_x$O$_3$ ($x=0$ and 0.1) using temperature-dependent magnetization and Raman spectroscopy over 200--400~K. Both compositions exhibit magnetic anomalies at 285.6 and 323~K, respectively, accompanied by correlated deviations of 12 Raman modes from their conventional anharmonic behavior. Principal component analysis and a global fitting approach reveal a common temperature-dependent phonon response, with mode-dependent amplitudes and signs. To interpret these anomalies, we develop a Landau-based spin-phonon coupling model describing complete, partial re-entrant, and incipient spin reorientation. Comparison with the experimental Raman profiles favors a partial, re-entrant rotation of the N'eel vector in both compositions, centered near 290~K. Ni substitution narrows the characteristic reorientation interval from approximately 116 to 84~K and enhances the magnetization anomaly by a factor of four. An additional feature near 262~K in LaFeO$_3$ is consistent with the Morin transition of trace $α$-Fe$_2$O$_3$. These findings suggest that partial spin reorientation can emerge without magnetic rare-earth ions and establish collective Raman phonon anomalies as a sensitive indirect probe of magnetic anisotropy changes in orthoferrites.

cond-mat.mtrl-sci↗