Noriyuki Hirota

Making water levitate

The levitation in air of water, other diamagnetic substances and even living organisms was recently achieved by using the extremely strong magnetic field provided by a Bitter-type hybrid magnet. We too have succeeded in levitating water, but in the lower fields of an ordinary 10 T superconducting magnet. To achieve this we make use of gravitational and magnetically induced buoyancy forces in the host paramagnetic atmosphere (pressurized air or oxygen), rather than simply the diamagnetic force on the levitating object, to balance the gravitational force. This permits the magnetic levitation in air of paramagnetic as well as diamagnetic substances, which was widely believed to be impossible. The physics underlying this effect is essentially the same as that of magnetohydrostatic ore separation, where a ferromagnetic fluid is used. Because our process can levitate subtances at a stable position in an atmosphere, we have named it ‘magneto-Archimedes levitation’.

Magnetic field enhancement of water vaporization

The water vaporization rate, an essential process for all the biological processes, was found to be significantly influenced under static magnetic fields up to 8 T in air and oxygen. The magnitude of the effect depended on the field–field gradient product B⋅dB/dx rather than on B itself. Under forced flow conditions of the atmosphere, both enhancement and suppression of the vaporization rate were observed depending upon the direction of the gas flow relative to the field gradient. A mechanism is proposed to explain the results in a systematic manner based on the assumption of the creation of magnetic wind driven by the gradient susceptibility distribution caused by water content distribution in the atmosphere. It is discussed that this magneto enhancement of vaporization may be the indirect cause of frequently reported field effects on living organisms.

Rise and Fall of Surface Level of Water Solutions under High Magnetic Field

Magnetic field effects on the surface profile have been investigated for water and copper sulfate aqueous solutions that have very small magnetic susceptibility. When a field of 10 T is applied in a horizontal superconducting magnet, the surface of distilled water was lowered by 39 mm at the field center, relative to the level at the zero field region (Moses effect). In contrast, the surface of a nearly saturated copper sulfate aqueous solution was raised by roughly the same height at the center (reversed Moses effect). The profiles were systematically explained based on the dia- and paramagnetic volume susceptibility values of distilled water and copper sulfate aqueous solution, respectively.

Effects of a magnetic field on the germination of plants

The effects of a nonuniform magnetic field on the germination of plants were studied. When a 10 T magnetic field was applied at the center of a superconducting magnet, a cucumber shoot germinating in a horizontal bore leaned towards the field center. In contrast, the root grew in the direction opposite the shoot. The observed result seemed to have occurred as a result of the magnetic force influencing the geotaxis of the cucumber. This idea was supported qualitatively by analysis results of the experimental data. Knowledge obtained in this study will be helpful for the evaluation of the effect of the magnetic field on living bodies and suggests the possibility of applying magnetic fields in other areas of research.

Magnetic field effects on water, air and powders

Magnetic fields up to 10 T have been applied on various substances composed of non-magnetic liquids, solids and/or gases. It has turned out that the magnetic fields of this range do produce various visible effects on the equilibrium shape, relative distribution of the substances or kinetic processes of the systems. The phenomena observed are due to the magnetization force that becomes non-significant in determining the mechanical balance of the system. The effects manifest themselves through the deformation of the equilibrium shape of the liquid interfaces, through the change in the effective weight which determines the relative positions occupied in the space by the substances involved and through the creation of convection in a non-uniform gas or liquid phase in terms of the magnetic susceptibility. Some of the processes seem to be utilized for practical purposes.

Thermal convection control by gradient magnetic field

A new technique to control thermal convection has been demonstrated by utilizing a gradient magnetic field. When the center of the superconducting magnet was fixed below the center of the heating region, the thermal convection flow was accelerated. In contrast, the convection flow was suppressed when the field center was fixed above the heating center, and under certain conditions, a reverse direction of flow was observed. The control of the flow was made possible by the experimental procedure, in which a downward flow was induced when the magnetic field was applied prior to the heating, and an upward flow was observed under the reverse procedure. These phenomena can be understood by taking account of the balance between the thermal driving force and the magnetic force acting on the air. A detailed analysis was made by examination of the temperature distribution in the observed system. The results suggest the possibility of using a gradient magnetic field for controlling thermal convection without any mec...

On-chip diamagnetic repulsion in continuous flow

Abstract We explore the potential of a microfluidic continuous flow particle separation system based on the repulsion of diamagnetic materials from a high magnetic field. Diamagnetic polystyrene particles in paramagnetic manganese (II) chloride solution were pumped into a microfluidic chamber and their deflection behaviour in a high magnetic field applied by a superconducting magnet was investigated. Two particle sizes (5 and 10 μm) were examined in two concentrations of MnCl2 (6 and 10%). The larger particles were repelled to a greater extent than the smaller ones, and the effect was greatly enhanced when the particles were suspended in a higher concentration of MnCl2. These findings indicate that the system could be viable for the separation of materials of differing size and/or diamagnetic susceptibility, and as such could be suitable for the separation and sorting of small biological species for subsequent studies.

Perpendicular magnetic anisotropy in CoFe2O4(001) films epitaxially grown on MgO(001)

We report on the magnetic properties of epitaxial cobalt-ferrite films with orientations parallel to [001] and [111] grown by a reactive molecular beam epitaxy method using pure ozone gas as an oxidation agent. Both Mossbauer spectroscopy and magnetization measurement of the CoFe2O4(001) film grown on MgO(001) indicate that the film has perpendicular magnetic anisotropy (PMA) with high coercivity, whereas the film of CoFe2O4(111) grown on α-Al2O3(0001) appears to be paramagnetic. The maximum uniaxial anisotropy energy for CoFe2O4(001) estimated from the magnetization and coercivity at room temperature is ≈3×106 erg/cm3.

Self-organization of nonmagnetic spheres by magnetic field

Two-dimensional crystallization of nonmagnetic gold spheres was achieved by the application of a high magnetic field. This phenomenon is based on the two different forces caused by a magnetic field; interactions between magnetic dipoles induced in the nonmagnetic spheres and magnetic force derived from field gradient. The former force is generally so weak and, hence, negligible. However, under an appropriate condition, we can achieve the subtle balance between the two forces. This phenomenon is a new class of self-assembling phenomena, and we believe that our achievement will be a milestone in the utilization of magnetic fields.

Magnetic field effect on interface profile between immiscible nonmagnetic liquids—Enhanced Moses effect

The change in the interface profile between immiscible nonmagnetic liquids was investigated quantitatively in a superconducting magnet with a large horizontal bore. The interface profile changed into concave down or up at the field center accordingly to the balance of magnetic susceptibilities between the lower and upper liquids. A flat interface was also demonstrated when the susceptibilities were balanced. It was found that modification of the interface profile was significantly amplified under an applied field as low as 1 T when the densities of the two liquids were quite close. The morphological change induced by the applied magnetic field can be used to remove a boundary, which initially separates two liquids without the field, and to initiate a mixing process or a chemical reaction between the two liquids.