Search

We report the results of magnetization, heat capacity, and neutron diffraction measurements on (Mo2/3RE1/3)2AlC with RE = Dy and Tb. Temperature and field-dependent magnetization as well as heat capacity were measured on a powder sample and on a single crystal allowing the construction of the magnetic field-temperature phase diagram. To study the magnetic structure of each magnetic phase, we applied neutron diffraction in a magnetic field up to 6 T. For (Mo2/3Dy1/3)2AlC in zero field, a spin density wave is stabilized at 16 K, with antiferromagnetic ordering at 13 K. Furthermore, we identify the coexistence of ferromagnetic and antiferromagnetic phases induced by magnetic fields for both RE = Tb and Dy. The origin of the field induced phases is resulting from the competing ferromagnetic and antiferromagnetic interactions.

Antiferomagnetsko stanje kubiˇcnog TbB6, ispod temperature prijelaza TN = 21 K i u magnetskim poljima do 6 T, istraživano je na monokristalu pomo´cu magnetske susceptibilnosti, magnetostrikcije i difrakcije x-zraka. Magnetska susceptibilnost i magnetostrikcija pokazuju tetragonalnu simetriju antiferomagnetske faze [1]. U njoj nastaju statiˇcki pomaci atoma u obliku valova, kao kompromis med¯udjelovanja izmjene i elasticˇnih sila [2]. Postoje tri ekvivalentne domene koje nastaju uz tetragonalnu deformaciju jediniˇcne ´celije duž jedne od triju glavnih osi kubiˇcnog kristala. U magnetskom polju domene poprimaju razli ˇcite energije. To omogu´cuje da primjenom magnetskog polja duž jedne od glavnih osi odaberemo domenu s najmanjom energijom ˇcime kristal postaje jednodomenski. Potrebna jakost polja ovisi o temperaturi što daje liniju selekcije domena u magnetskom faznom dijagramu. Naglom promjenom smjera polja u drugu os zapoˇcinje nukleacija i rast druge domene. Brzina ovog procesa ovisi o jakosti polja i o temperaturi. U ovom radu istražujemo dinamiku rasta antiferomagnetske domene promatranjem vremenske promjene magnetostrikcije. Prikazani su rezultati mjerenja magnetostrikcije kao funkcije vremena nakon nagle promjene smjera magnetskog polja, za razne jakosti polja i temperature. Diskutiran je oblik linije selekcije domene u magnetskom faznom dijagramu i vremenska ovisnost magnetostrikcije. [1] R. M. Galéra, M. Amara, I. Aviani, F. Givord, F. Zontone, and S. Kunii, Phys. Stat. Sol. (c) 3 (2006) 3184 [2] M. Amara, R.-M. Galéra, I. Aviani, and F. Givord, Phys. Rev. B 82 (2010) 214414

The antiferromagnetic (AFM) ground state of cubic TbB6 is characterized by multiaxial ordering and a complex magnetic phase diagram. Magnetic susceptibility and magnetostriction show a tetragonal symmetry of AFM phase [1]. The x-ray diffraction shows the charge reflections resulting from the formation of static atomic displacement waves which can be described as a compromise between the exchange and a single-ion elastic couplings [2]. The single crystal of TbB6 is studied at the first order AFM phase transition and within the ordered phase by means of magnetostriction and anisotropic magnetic susceptibility in magnetic fields up to 6 T. The tetragonal AFM phase below TN = 21 K is a mixture of three equivalent AFMdomains. Based on the symmetry of spontaneous deformation and the magnetostriction data we conclude that Tb magnetic moments lay in the tetragonal plane. If we apply magnetic field of about 5 T along one of the fourfold axes, the energetically most favorable domain is selected, and the whole crystal tunes into a single-domain state. This state is stable even in zero magnetic field. The observed behaviors are consistent with the tetragonal symmetry of the AFM state. In this work we discuss the the domain selection line observed in the magnetic phase diagram. We relate this line to the measured anisotropic magnetic susceptibilities and the magnetic energy difference for the magnetic field applied along the two characteristic directions of AFM domain. For a sudden change of the field direction to another fourfold axis the nucleation and the growth of another domain emerge. We attain to explain the temperature and field dependent time evolution of this process. We use the time dependence of magnetostriction to study the domain nucleation and growth dynamics. [1] R. M. Galéra, M. Amara, I. Aviani, F. Givord, F. Zontone, and S. Kunii, Phys. Stat. Sol. (c) 3 (2006) 3184 [2] M. Amara, R.-M. Galéra, I. Aviani, and F. Givord, Phys. Rev. B 82 (2010) 214414

The antiferromagnetic state of TbB6 has been investigated by means of magnetic susceptibility, magnetostriction and X-ray diffraction measurements on a single crystal. The anisotropy of the magnetic susceptibility and the magnetostriction data point to a tetragonal symmetry in the antiferromagnetic state. Below TN, the X-ray diffraction investigation shows charge satellites, related to the and h wave vectors stars, similar to those observed in GdB6. The satellites clearly result from the formation of static atomic displacements waves. The displacive phenomenon is described as a compromise between the exchange coupling and a single-ion elastic energy. This mechanism is shown to be responsible for the recurrence of the h i magnetic wave vectors in rare-earth hexaborides. A combined analysis of experimental and theoretical data points to only two stable tetragonal models for TbB6 antiferromagnetic structure. This study confirms the influence of exchange displacements in rare-earth hexaborides and highlights the need for a systematic investigation of the magnetic anisotropy of antiferromagnets

Due to orbital degeneracy, a 4f electronic shell has the ability to distort when influenced by an electrostatic, magnetic or collective intersite field. In case of collective phenomena, the 4f asphericity which develops may result in a strain mode and/or introduce a new charge periodicity. The first is accessible via dilatometric techniques whereas the second needs a microscopic probe, X-rays, to be detected.