Marko Jagodič

Orientational Order-Magnetization Coupling in Mixtures of Magnetic Nanoparticles and the Ferroelectric Liquid Crystal

We have studied the ferroelectric SmC* phase of SCE9 ferroelectric liquid crystal (LC) mixtures with magnetic nanoparticles (NPs). The impact of the NPs on the Goldstone and soft mode dielectric response has been determined by the dielectric spectroscopy measurements. The possible indirect coupling between the magnetic moments and the electrical polarization has been verified by measuring the impact of the electrical field on the magnetic susceptibility via SQUID susceptometer measurements. The disordering effects on the ferroelectric phase transition have been studied by the high resolution calorimetry. Similar disordering effects have been found as in the case of the aerosil particles [1, 2].

A thermal memory cell

We present a concept of a new kind of memory element, a thermal memory cell, where a byte of digital information can be stored into the storage medium by pure thermal manipulation. Thermal inscription of information employs a specific temperature-time profile that involves continuous cooling and isothermal waiting time periods in the absence of any external magnetic or electric field. Our storage media are magnetically frustrated solids. We succeeded to thermally write arbitrary American Standard Code for Information Interchange characters into the Taylor-phase T-Al3(Mn,Fe) complex intermetallic compound and the Cu–Mn canonical spin glass. Besides for data storage, the concept may be employed for secure data transfer and for retrieving cosmological information from extraterrestrial dust particles.

Multiferroic Behaviour in Mixtures of the Ferroelectric Liquid Crystal and Magnetic Nanoparticles

A dielectric spectroscopy, magnetic susceptibility and high resolution calorimetry have been carried out in the vicinity of the ferroelectric smectic C* phase of SCE9 ferroelectric liquid crystal (LC) mixtures with magnetic nanoparticles (NPs) to determine the impact of the magnetic nanoparticles on the Goldstone and soft mode and to study the disordering effects on the ferroelectric phase transition. It was verified via SQUID susceptometer that the indirect coupling between the NPs magnetic moments and the LC electrical polarization exists in these mixtures.

Anisotropic electrical, magnetic and thermal transport properties of the Al80Cr15Fe5 decagonal approximant

The anisotropic magnetic, electrical and thermal transport properties were studied of a single-crystalline Al80Cr15Fe5 approximant to the decagonal quasicrystal. The temperature-dependent electrical resistivity along the b and c crystalline directions shows non-metallic behaviour with a broad maximum, whereas it exhibits a metallic positive temperature coefficient along the a direction perpendicular to the (b, c) atomic planes. The resistivity can be treated with the model of slow charge carriers, where the increased electron–phonon scattering upon raising the temperature induces a transition from dominant Boltzmann (metallic) to dominant non-Boltzmann (insulating-like) regime. The magnetic susceptibility and thermal conductivity also reveal a small anisotropy.

Competing antiferromagnetism and local magnetic order in the bulk ceramic PZT-PFW multiferroic system: searching for the most promising ratio between PZT and PFW

Bulk ceramic compounds of formula xPZT+(1 − x)PFW, where PZT = Pb(Zr0.575Ti0.425)O3 and PFW = Pb(Fe2/3W1/3)O3, for x = 0.15; 0.20; 0.25; 0.37; 0.50; 0.60; 0.65; 0.70 and 0.80, were synthesized. In these single phase perovskites a change from rhombohedral to cubic structure is observed as the proportion of PFW increases. Magnetic investigations including zero-field cooled and field-cooled magnetization versus temperature measurements, magnetic hysteresis loops measurement and ac susceptibility measurements were performed. At high temperatures a clear antiferromagnetic (AFM)-like transition was observed for high PFW concentrations. The low temperature behaviour indicated spin freezing and thermal activation of magnetic moments and measurements confirmed the existence of a barrier maximum for x = 0.37. Competition between the long-range AFM order and short-range magnetic ordering of small nano-sized regions with finite magnetic moments was observed in the studied system. (Some figures may appear in colour only in the online journal)

Mixtures of Magnetic Nanoparticles and the Ferroelectric Liquid Crystal: New Soft Magnetoelectrics

A mixture of maghemite ferromagnetic nanoparticles and the ferroelectric liquid crystal Felix 015/100 was experimentally analysed in the vicinity of the ferroelectric smectic C* (SmC*) phase. In order to verify the existence of magnetoelectricity in prepared soft material, a SQUID-based magnetometer was used. It was shown that the orientation of magnetic nanoparticles is directly coupled to the liquid crystal molecular director field. Such coupling allows possibility of indirect coupling between the nanoparticle magnetization and liquid crystal polarization. This makes such mixtures potential for new soft magnetoelectrics.

Low temperature magnetic behaviour of PZT-PFW bulk multiferroic ceramics

Combining the ferroelectric and magnetic components into the solid solution, it is expected to obtain the magneto-electric multiferroic material. Novel bulk ceramic compounds xPZT+(1 − x)PFW, where PZT = Pb(Zr0.575Ti0.425)O3 and PFW = Pb(Fe2/3W1/3)O3, for x = 0.15, 0.20, 0.25, 0.50, 0.70, 0.80 were synthesized and their magnetic investigation was performed, including the measurement of zero-field cooled (ZFC) and field-cooled (FC) magnetization curves, magnetic hysteresis loops and AC susceptibility. In the low temperature region (below 20 K) splitting between the ZFC and FC curves together with the frequency dependent peaks in AC susceptibility point to the glassy freezing/blocking of magnetic moments and magnetic relaxor-like behaviour.

Phase Ordering in Mixtures of Liquid Crystals and Nanoparticles

We have studied the coupling interaction between liquid crystal (LC) molecules and nanoparticles (NPs) in LC=NPs mixtures. Using a simple phenomenological approach, possible structures of the coupling term are derived for strongly anisotropic NPs. The coupling terms include (i) an interaction term promoting the mutual ordering of the LC molecules and the NPs, and (ii) the Flory-Huggins-type term enforcing the phase separation. Both contributions exhibit the same scaling dependence on the diameter of the NPs. However, these terms only exist for a finite degree of nematic LC ordering. The magnetic response due to the LC-NPs coupling is probed experimentally for a mixture of weakly anisotropic magnetic NPs and a ferroelectric LC. A finite coupling effect was observed in the ferroelectric LC phase, suggesting such systems can be used as soft magnetoelectrics.

Indirect Magnetoelectric Coupling in Mixtures of Magnetite and Ferroelectric Liquid Crystal

The existence of an indirect magnetoelectricity in a soft composite material prepared as a mixture of magnetite ferromagnetic nanoparticles (NPs) and the ferroelectric liquid crystal (FLC) Felix 015/100 was verified by using a SQUID-based magnetometer. It was observed that the orientation of nanoparticles is directly coupled to the liquid crystal director field. Such a coupling allows the possibility of indirect coupling between the magnetic and ferroelectric order. This gifts the mixtures of FLC and magnetic nanoparticles (MNPs) with a great potential for soft indirect magnetoelectrics.

The influence of thermal annealing on structural order in the μ-Al4Mn complex intermetallic

Abstract The influence of cooling rate on structural order in the complex hexagonal μ-Al4Mn phase was investigated. As higher magnetizations are detected in more disordered samples, the short-scale disorder was studied indirectly by magnetic measurements. The magnetizations of as-grown samples and samples subjected to different thermal treatments were compared. It was found that water-quenching increases the disorder in the crystal structure regardless of previous thermal history. Qualitatively the same results were obtained for the quasicrystalline i-Al—Pd—Mn phase where the changes in magnetic properties and consequently in the degree of structural order for different thermal treatments were even more pronounced.