Longitudinal remagnetization of uniaxial antiferromagnetic nanoparticles: the role of spontaneous magnetic moment

A kinetic theory of magnetic response of uniaxial antiferromagnetic nanoparticles is presented. Within the developed framework, a particular case when an external field is applied strictly along the anisotropy axis is considered in detail. Analysis of the relaxation spectrum of an antiferromagnetic particle with a spontaneous magnetic moment is performed. It is shown that in a wide frequency range the magnetic response of such particle is determined entirely by the relaxation mode with the longest time. An analytical expression for this time that explicitly contains a value of the decompensation magnetic moment is derived. Also, simple formulae for both static and dynamic longitudinal magnetic susceptibility of an antiferromagnetic nanoparticle are obtained. According to them, longitudinal susceptibility grows quadratically with the value of the spontaneous magnetic moment. Besides, if the latter is not zero, the change of the static susceptibility with temperature turns out to be non-monotonic. The influence of the spontaneous magnetic moment of the particle on the magnetization curves in strong fields is analysed using both energy approach and kinetic theory. The calculated dependences of the dynamic coercivity on the amplitude and variation rate of the applied field are qualitatively compared with experimental data. This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.

Directed synthesis of a hybrid improper magnetoelectric multiferroic material

Preparing materials which simultaneously exhibit spontaneous magnetic and electrical polarisations is challenging as the electronic features which are typically used to stabilise each of these two polarisations in materials are contradictory. Here we show that by performing low-temperature cation-exchange reactions on a hybrid improper ferroelectric material, Li2SrTa2O7, which adopts a polar structure due to a cooperative tilting of its constituent TaO6 octahedra rather than an electronically driven atom displacement, a paramagnetic polar phase, MnSrTa2O7, can be prepared. On cooling below 43 K the Mn2+ centres in MnSrTa2O7 adopt a canted antiferromagnetic state, with a small spontaneous magnetic moment. On further cooling to 38 K there is a further transition in which the size of the ferromagnetic moment increases coincident with a decrease in magnitude of the polar distortion, consistent with a coupling between the two polarisations.

Observation of strong excitonic magneto-chiral anisotropy in twisted bilayer van der Waals crystals

The interplay between chirality and magnetism generates a distinct physical process, the magneto-chiral effect, which enables one to develop functionalities that cannot be achieved solely by any of the two. Such a process is universal with the breaking of parity-inversion and time-reversal symmetry simultaneously. However, the magneto-chiral effect observed so far is weak when the matter responds to photons, electrons, or phonons. Here we report the first observation of strong magneto-chiral response to excitons in a twisted bilayer tungsten disulfide with the amplitude of excitonic magneto-chiral (ExMCh) anisotropy reaches a value of ~4%. We further found the ExMCh anisotropy features with a spectral splitting of ~7 nm, precisely the full-width at half maximum of the excitonic chirality spectrum. Without an externally applied strong magnetic field, the observed ExMCh effect with a spontaneous magnetic moment from the ferromagnetic substrate of thulium iron garnet at room temperature is favorable for device applications. The unique ExMCh processes provide a new pathway to actively control magneto-chiral applications in photochemical reactions, asymmetric synthesis, and drug delivery.

Observation of strong excitonic magneto-chiral anisotropy in twisted bilayer van der Waals crystals

The interplay between chirality and magnetism generates a distinct physical process, the magneto-chiral effect, which enables one to develop functionalities that cannot be achieved solely by any of the two. Such a process is universal with the breaking of parity-inversion and time-reversal symmetry simultaneously. However, the magneto-chiral effect observed so far is weak when the matter responds to photons, electrons, or phonons. Here we report the first observation of strong magneto-chiral response to excitons in a twisted bilayer tungsten disulfide with the amplitude of excitonic magneto-chiral (ExMCh) anisotropy reaches a value of ~4%. We further found the ExMCh anisotropy features with a spectral splitting of ~7 nm, precisely the full-width at half maximum of the excitonic chirality spectrum. Without an externally applied strong magnetic field, the observed ExMCh effect with a spontaneous magnetic moment from the ferromagnetic substrate of thulium iron garnet at room temperature is favorable for device applications. The unique ExMCh processes provide a new pathway to actively control magneto-chiral applications in photochemical reactions, asymmetric synthesis, and drug delivery.

Influence of Ru on the Magnetic Properties of Y2T17 (T = Co, Fe)

Influence of Ru substitution on magnetic properties of Y2Fe17and Y2Co17(hexagonal structure of the Th2Ni17-type) has been studied on single-crystalline samples. Whereas in the Y2Fe17-xRuxsystem ferromagnetism is transformed rapidly into antiferromagnetism with a field-induced metamagnetic transition, in Y2Co17-xRuxonly a monotonous decrease of spontaneous magnetic moment, Curie temperature and first anisotropy constant is observed.

Transition from Itinerant Electron Magnetism to Localized Spin Magnetism in Ni3Al1-YMny Alloys

Magnetic properties of Ni3Al1-yMny alloys at y≤0.6 were investigated at T≤400 K in magnetic fields H≤4 MA/m. The concentration y dependencies of the spontaneous magnetic moment s, the effective magnetic moment eff, the Curie temperature ТС, the Weiss constant , and the temperature independent part of the magnetic susceptibility 0 were determined. The behavior of the Rhodes-Wohlfarth parameter р(y) in the transition region from the itinerant electron magnetism to the spin localized one is related to the increase in the spontaneous magnetic moment of Ni atoms inversely proportional to the average distance between Mn atoms with the highly localized magnetic moments.

MAGNETIC PROPERTIES Cu DOPED ZnO:Fe SEMICONDUCTORS

Magnetization measurements were performed on a series of Zn 0.9-x Fe 0.1 Cu x O samples (0 ≤ x ≤ 0.10). Small hysteresis losses are seen at low temperatures. The ferromagnetic exchange interaction has been evaluated from the inverse DC magnetic susceptibility versus T and the molecular field theory. We found that Cu -doping greatly enhances the FM exchange interaction, increases the saturation magnetization, hysteresis losses and the magnetic susceptibility. Arrott-Kouvel plot has been used to study the spontaneous magnetic moment at low temperatures. We show that hysteresis losses cannot be taken as the only evidence for the appearance of the ferromagnetic order in these semiconducting semi-magnetic materials.