Mise en page 1 - Laboratoire National des Champs Magnétiques ...

MAGNET DEVELOPMENT AND INSTRUMENTATION 2009A new magnetometer for use in dc magnetic fields in excess of 28 T.Since many years we have developed intense collaborationwith French and foreign groups in the frame of the studyof the magnetic properties of solids under strong magneticfield and that in the 1.5 − 400 K temperature range. In2009 these exchanges with different groups (France, USA,Poland, Turkey, Romania, Canada.) have been then maintained.A new challenge originates from the capability ofproduction of continuous magnetic field at the 35 T level(M9 magnet). Such a field value leads to an important reductionof the inner bore of the magnet that does not exceed34 mm. The construction of a new home-made magnetometerwas under taken in the second half of the year2008. In March 2009, this new magnetometer has been successfullytested on the M9 magnet with magnetic fields upto 35 T in the 1.5 − 350 K temperature range. It is worthnoting that the two main challenges were (i) one uniquesample holder which can be used either in a 50 mm boreor in a 34 mm bore in Grenoble or in the Vibrating SampleMagnetometer in the NHMFL (Tallahassee USA). Thischoice allows an accurate comparisons of the magnetization(M) values delivered by the different magnetometers underidentical experimental conditions; (ii) Precise absolute calibrationof the magnetometer was performed using differentsingle crystals.Finally, the set sup offers the advantage of a good sensitivityin the order of 2 × 10 −3 emu; the relative accuracy isestimated to be 0.1% when M is of the order of one emu,while the reproducibility on the field and on temperatureare estimated to be 0.01 T and 0.2 K, respectively. Thesample cavity is a cylinder whose axis is parallel to the appliedmagnetic field; its volume is of about 125 mm 3 inthe 4.2 − 400 K temperature range. In the 1.5 − 4.2 K domain(pumped helium bath) the available diameter of thesample increases up to 12 mm. The sample may be eitherpowder or oriented powder or single crystal. Isothermal orisofield magnetization curves may be obtained in positiveand (or) negative field. The quality of the measurementsperformed using this new home made magnetometer is illustratedby the figures 182 and 183. From each isothermalM T (H) obtained for the deuteride Y 0.7 Er 0.3 Fe 2 (D) 4.2the temperature variation of the differential magnetic susceptibility(dM/dH)T versus the applied field was deduced(figure 182). The critical field of the transition is then definedas the field corresponding to the maximum.In November 2009, in collaboration with the Academy ofSciences of Prague magnetic measurements under pressure(P up to 11 kbar) were performed. Although the new M1magnet failed in relatively low field (100 kOe) the figure183 shows that measurements of excellent quality canbe performed. In the following month further experimentsare expected with H up to 330 kOe in the 1.6 − 4.2 K temperaturerange.Figure 182: Differential magnetic susceptibility versus appliedfield (up to 35 T) for the Y 0.7 Er 0.3 Fe 2 (D) 4.2 deuteride.Figure 183: Isothermal magnetization curves for the Ce 2 Fe 17alloy at 4.2 K under different pressures.M. GuillotA. Zdenek, K. Jiri, S. Yuriy, M. Martin, (Institute of Physics, The Academy of Sciences of the Czech Republic, Prague)C.V. Colin, O. Isnard (Institut Néel, CNRS and Université Joseph Fourier)128