Advanced Seminar on Condensed Matter Physics

Sommersemester 2017

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INF 227, SR 1.403
11:15 h

25.7.2017 11:15 h
Dr. Rabindranath Bag, IISER Pune
INF 227, SR 1.403

Low-dimensional quantum magnets are presently an interesting field of study because of their unique and non-trivial properties. Sr14Cu24O41, a well-studied quasi-one-dimensional quantum magnet consisting of a hybrid chain/ladder structure. The ladders in this compound are known to exhibit a spin-singlet ground state, whereas the chains harbor spin-1/2 dimers that form an intervening Zhang-Rice singlet. The presence of some residual ‘free’ spins in the chain exhibit long-distance quantum entanglement at low temperatures [1]. We have grown high quality single crystals of Sr14Cu24O41doped with dilute magnetic and nonmagnetic impurities, using the TSFZ method [2]. We investigate the effect of dilute doping (< 1 %) on the spin-dimerization in the chain sublattice using susceptibilities and specific heat. The dimerization gap remains isotropic and constant in magnitude upon doping with Zn, Ni and Al. However, with Co-doping, we witness an anisotropic closing of the dimerization gap; for H || chain, the gap supresses rapidly, whereas the gap remains almost unchanged for the perpendicular to chain.

Last part, I will be talking on a new system, named orthoferrites (RFeO3). Recently, we have performed highly sensitive torque magnetometry measurement on single crystals of HoFeO3 along crystallographic directions. Since the paramagnetic contribution exerts no torque, a detailed investigation of the ordered Fe moments as a function of temperature and magnetic field is carried out. In addition to the spin reorientation transition, we found a weak and continuous transition sets in below a temperature of ~220 K and a spin-switching transition above the room temperature.

[1] S. Sahling et. al. Nature Physics 11, 255-260 (2015)

[2] R. Bag et. al. Journal of Crystal Growth 458, 16-26 (2017)