Martin R. Lees

Field-Induced Magnetization Steps in Intermetallic Compounds and Manganese Oxides: The Martensitic Scenario

Field-induced magnetization jumps with similar characteristics are observed at low temperature for the intermetallic germanide

Quantum tunneling of the magnetization in the Ising chain compound Ca3Co2O6

{\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}

Nature of the magnetic order in Ca3Co2O6.

and the mixed-valent manganite

The nature of the magnetic order in Ca3Co2O6

{\mathrm{Pr}}_{0.6}{\mathrm{Ca}}_{0.4}{\mathrm{Mn}}_{0.96}{\mathrm{Ga}}_{0.04}{\mathrm{O}}_{3}.

Preparation and characterization of polyethylenimine-coated Fe3O4-MCM-48 nanocomposite particles as a novel agent for magnet-assisted transfection.

We report that the field location\char22{}and even the existence\char22{}of these jumps depends critically on the magnetic field sweep rate used to record the data. It is proposed that, for both compounds, the martensitic character of their antiferromagnetic-to-ferromagnetic transitions is at the origin of the magnetization steps.

Specific heat and magnetization study on single crystals of the frustrated quasi-one-dimensional oxideCa3Co2O6

The magnetic behavior of the Ca3Co2O6 spin chain compound is characterized by a large Ising-like character of its ferromagnetic chains, set on a triangular lattice, that are antiferromagnetically coupled. At low temperature, T < 7 K, the 3D antiferromagnetic state evolves towards a spin frozen state. In this temperature range, magnetic field driven magnetization of single crystals (H // chains) exhibits stepped variations. The occurrence of these steps at regular intervals of the applied magnetic field, Hstep = 1.2 T, is reminiscent of the quantum tunneling of the magnetization (QTM) of molecular based magnets. Magnetization relaxation experiments also strongly support the occurrence of this quantum phenomenon. This first observation of QTM in a magnetic oxide belonging to the large family of A3BB′O6 compounds opens new opportunities to study a quantum effect in a very different class of materials from molecular magnets.

Higgs transition from a magnetic Coulomb liquid to a ferromagnet in Yb2Ti2O7

We present a detailed powder and single-crystal neutron diffraction study of the spin chain compound Ca3Co2O6. Below 25 K, the system orders magnetically with a modulated partially disordered antiferromagnetic structure. We give a description of the magnetic interactions in the system which is consistent with this magnetic structure. Our study also reveals that the long-range magnetic order coexists with a shorter-range order with a correlation length scale of approximately 180 angstroms in the ab plane. Remarkably, on cooling, the volume of material exhibiting short-range order increases at the expense of the long-range order.

Structural, spectroscopic, magnetic and electrical characterization of Ca-doped polycrystalline bismuth ferrite, Bi1−xCaxFeO3−x/2 (x ≤ 0.1)

We present a detailed powder and single-crystal neutron diffraction study of the spin chain compound Ca3Co2O6. Below 25 K, the system orders magnetically with a modulated partially disordered antiferromagnetic structure. We give a description of the magnetic interactions in the system which is consistent with this magnetic structure. Our study also reveals that the long-range magnetic order coexists with a shorter-range order with a correlation length scale of approximately 180 angstroms in the ab plane. Remarkably, on cooling, the volume of material exhibiting short-range order increases at the expense of the long-range order.

Insulator–metal transitions in Pr0.7Ca0.3MnO3 induced by a magnetic field

A new type of magnetic nanoparticle was synthesized using mesoporous silica MCM-48 as a template. Magnetite (Fe(3)O(4)) nanocrystals were incorporated onto the MCM-48 silica structure by thermal decomposition of iron(III) acetylacetonate. The particle size of these Fe(3)O(4)-MCM-48 composite particles is around 300 nm with an iron oxide content of ca. 20% w/w. Measurements from SQUID magnetometry suggest that these nanoparticles possess superparamagnetic properties similar to those of Fe(3)O(4) nanoparticles. By coating positively charged polyethylenimine on to the surface, DNA can be bound onto the Fe(3)O(4)-MCM-48 nanoparticles. Transfection studies showed that these PEI-Fe(3)O(4)-MCM-48 particles were highly effective as a transfection reagent, and a 400% increase of transfection efficiency compared with the commercial products was recorded.

Evidence for superconductivity with broken time-reversal symmetry in locally noncentrosymmetric SrPtAs

Specific heat and magnetization measurements have been carried out under a range of magnetic fields on single crystals of Ca 3 Co 2 O 6 . This compound is composed of Ising magnetic chains that are arranged on a triangular lattice. The intrachain and interchain couplings are ferromagnetic and antiferromagnetic, respectively. This situation gives rise to geometrical frustration, that bears some similarity to the classical problem of a two-dimensional Ising triangular antiferromagnet. This paper reports on the ordering process at low T and the possibility of one-dimensional features at high T.