Search for: All records

Many technologically useful magnetic oxides are ferrimagnetic insulators, which consist of chemically distinct cations. Here, we examine the spin dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite (Ni0.65Zn0.35Al0.8Fe1.2O4) under continuous microwave excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance to separately probe Fe2+/3+ and Ni2+ cations on different sublattice sites. Our results show that the precessing cation moments retain a rigid, collinear configuration to within ≈2°. Moreover, the effective spin relaxation is identical to within <10% for all magnetic cations in the ferrite. Thus, we validate the oft-assumed “ferromagnetic-like” dynamics in the resonantly driven ferrimagnetic oxide: the magnetic moments from different cations precess as a coherent, collective magnetization, despite the high contents of nonmagnetic Zn2+ and Al3+ diluting the exchange interactions. 

Abstract We present the first theoretical and experimental evidence of time-resolved dynamic x-ray magnetic linear dichroism (XMLD) measurements of GHz magnetic precessions driven by ferromagnetic resonance in both metallic and insulating thin films. Our findings show a dynamic XMLD in both ferromagnetic Ni₈₀Fe₂₀and ferrimagnetic Ni_0.65Zn_0.35Al_0.8Fe_1.2O₄for different measurement geometries and linear polarizations. A detailed analysis of the observed signals reveals the importance of separating different harmonic components in the dynamic signal in order to identify the XMLD response without the influence of competing contributions. In particular, RF magnetic resonance elicits a large dynamic XMLD response at the fundamental frequency under experimental geometries with oblique x-ray polarization. The geometric range and experimental sensitivity can be improved by isolating the 2ωFourier component of the dynamic response. These results illustrate the potential of dynamic XMLD and represent a milestone accomplishment toward the study of GHz spin dynamics in systems beyond ferromagnetic order. 

A search for proton decay into $e^{+}/{\mu }^{+}$and a $\eta$meson has been performed using data from a $0.373\mathrm{Mton}·\mathrm{year}$exposure (6050.3 live days) of Super-Kamiokande. Compared to previous searches this work introduces an improved model of the intranuclear $\eta$interaction cross section, resulting in a factor of 2 reduction in uncertainties from this source and $\sim 10\%$increase in signal efficiency. No significant data excess was found above the expected number of atmospheric neutrino background events resulting in no indication of proton decay into either mode. Lower limits on the proton partial lifetime of $1.4\times {10}^{34}\mathrm{years}$for $p\to e^{+}\eta$and $7.3\times {10}^{33}\mathrm{years}$for $p\to {\mu }^{+}\eta$at the 90% CL were set. These limits are around 1.5 times longer than our previous study and are the most stringent to date. Published by the American Physical Society2024 

The Super-Kamiokande and T2K Collaborations present a joint measurement of neutrino oscillation parameters from their atmospheric and beam neutrino data. It uses a common interaction model for events overlapping in neutrino energy and correlated detector systematic uncertainties between the two datasets, which are found to be compatible. Using 3244.4 days of atmospheric data and a beam exposure of $19.7\left(16.3\right)\times {10}^{20}$protons on target in (anti)neutrino mode, the analysis finds a $1.9\sigma$exclusion of $CP$conservation (defined as $J_{CP}=0$) and a $1.2\sigma$exclusion of the inverted mass ordering. Published by the American Physical Society2025 

We present the results of the charge ratio ( $R$) and polarization ( $P_0^{\mu }$) measurements using decay electron events collected between September 2008 and June 2022 with the Super-Kamiokande detector. Because of its underground location and long operation, we are able to perform high-precision measurements by accumulating cosmic-ray muons. We measured the muon charge ratio to be $R=1.32\pm 0.02(\mathrm{stat}+\mathrm{syst})$at $E_{\mu }\cos {\theta }_{\text{Zenith}}={0.7}_{-0.2}^{+0.3}\mathrm{TeV}$, where $E_{\mu }$is the muon energy and ${\theta }_{\text{Zenith}}$is the zenith angle of incoming cosmic-ray muons. This result is consistent with the Honda flux model while indicating a tension with the $\pi K$model of $1.9\sigma$. We also measured the muon polarization at the production location to be $P_0^{\mu }=0.52\pm 0.02(\mathrm{stat}+\mathrm{syst})$at the muon momentum of ${0.9}_{-0.1}^{+0.6}\mathrm{TeV}/c$at the surface of the mountain; this also suggests a tension with the Honda flux model of $1.5\sigma$. This is the most precise measurement ever to experimentally determine the cosmic-ray muon polarization near $1\mathrm{TeV}/c$. These measurement results are useful to improve atmospheric neutrino simulations. Published by the American Physical Society2024