Terahertz time domain spectroscopic investigation of spin reorientation transitions in HoFeO3.

Both continuous and discontinuous spin reorientation transitions in the HoFeO3 orthoferrite have been further investigated in this paper. Here, we use terahertz spectroscopy through the terahertz ferromagnetic and antiferromagnetic resonances to study the thermodynamics of the spin reorientation transitions in HoFeO3 ceramics. The spin reorientations are driven by changes in the anisotropy energy, and the spin moments in and out of the (a, c) plane correspond to the continuous transitions and discontinuous transitions. We fitted the antiferromagnetic resonant frequencies, and we achieved quantitative insight on the changes in anisotropy energy. Measuring M-H (moment-magnetic field) curves, we found changes in macroscopic magnetization and verified the thermodynamics.

Integrative Lighting Aimed at Patients with Psychiatric and Neurological Disorders.

The purpose of this paper is to investigate the impact of circadian lighting-induced melatonin suppression on patients with psychiatric and neurological disorders in hospital wards by using an ad-hoc metrology framework and the subsequent metrics formalized by the CIE in 2018. A measurement scheme was conducted in hospital ward rooms in the Department of Neurology, Zealand University Hospital, at Roskilde in Denmark, to evaluate the photometric and colorimetric characteristics of the lighting system, as well as its influence on the circadian rhythm of the occupants. The measurement scheme included point measurements and data logging, using a spectrophotometer mounted on a tripod with adjustable height to assess the newly installed circadian lighting system. The measured spectra were uploaded to the Luox platform to calculate illuminance, CCT, MEDI, etc., in accordance with the CIE S026 standard. Furthermore, the MLIT based on MEDI data logging results was calculated. In addition to CIE S026, we have investigated the usefulness of melatonin suppression models for the assessment of circadian performance regarding measured light. From the results, the lighting conditions in the patient room for both minimal and abundant daylight access were evaluated and compared; we found that access to daylight is essential for both illumination and circadian entrainment. It can be concluded that the measurement scheme, together with the use of the Luox platform and Canva template, is suitable for the accurate and satisfactory measurement of integrative lighting that aligns with CIE requirements and recommendations.

Rare Earth Orthoferrite Tuning of Transmitted Waves as Natural Metamaterials.

Metamaterials display many electromagnetic properties, such as the manipulation of electromagnetic waves through the arrangement of small discrete structures. However, complex designs of mechanically or electrically patterned structures are required to modify these properties. We report on the use of rare earth orthoferrites to tune transmitted waves by engineering the thickness, composition, and temperature using terahertz (THz) time-domain spectroscopy. The modeling of the process of manipulating the transmitted waves helps to elucidate the manipulated amplitude, transmittance, peak height, and frequency. The effectiveness of thickness engineering in tuning the transmitted waves, which conformed to the Beer-Lambert law, was demonstrated. The transmitted waves were also strongly affected by doping. In addition, a thermal anisotropic energy manipulation approach to tuning transmitted waves was developed by lowering the temperature. Rare earth orthoferrites are a kind of effective medium in the THz range and exhibit the signature of natural metamaterials.

Mode jumping of split-ring resonator metamaterials controlled by high-permittivity BST and incident electric fields.

We investigate the resonant modes of split-ring resonator (SRR) metamaterials that contain high-permittivity BST block numerically and experimentally. We observe interesting mode-jumping phenomena from the BST-included SRR absorber structure as the excitation wave is incident perpendicularly to the SRR plane. Specifically, when the electric field is parallel to the SRR gap, the BST block in the gap will induce a mode jumping from the LC resonance to plasmonic resonance (horizontal electric-dipole mode), because the displacement current excited by the Mie resonance in the dielectric block acts as a current channel in the gap. When the electric field is perpendicular to the gap side, the plasmonic resonance mode (vertical electric-dipole mode) in SRR changes to two joint modes contributed simultaneously by the back layer, SRR and BST block, as a result of connected back layer and SRR layer by the displacement current in the BST dielectric block. Based on the mode jumping effect as well as temperature and electric-field dependent dielectric constant, the BST-included SRR metamaterials may have great potentials for the applications in electromagnetic switches and widely tunable metamaterial devices.

Ultralow temperature terahertz magnetic thermodynamics of perovskite-like SmFeO3 ceramic.

The terahertz magnetic properties of perovskite-like SmFeO3 ceramic are investigated over a broad temperature range, especially at ultralow temperatures, using terahertz time-domain spectroscopy. It is shown that both resonant frequencies of quasi-ferromagnetic and quasi-antiferromagnetic modes have blue shifts with the decreasing temperature due to the enhancement of effective magnetic field. The temperature-dependent magnetic anisotropy constants are further estimated using the resonant frequencies, under the approximation of omitting the contribution of Sm(3+) magnetic moments to the effective field. Specially, the effective anisotropy constants in the ca and cb planes at 3 K are 6.63 × 10(5) erg/g and 8.48 × 10(5) erg/g, respectively. This thoroughly reveals the terahertz magnetic thermodynamics of orthoferrites and will be beneficial to the application in terahertz magnetism.