I.E.H.M Hagmusa

A specific-heat study of RMn4Al8 compounds (R=Y, La, Pr, Nd, Dy, Er)

Abstract Specific-heat measurements have been performed on the tetragonal ThMn 12 -type RMn 4 Al 8 compounds with R=Y, La, Pr, Nd, Dy and Er in the temperature range 1.5 to 200 K. The compound PrMn 4 Al 8 gives rise to a λ-type anomaly at 14 K. No anomalies indicative of magnetic ordering were found above 1.5 K in the specific-heat curves of the RMn 4 Al 8 compounds with R=Y, La, Nd, Dy, and Er. From the temperature dependence of the magnetic entropy, it is concluded that the overall crystal-field splitting in the compounds with R=Pr, Nd, Dy, and Er is of the order of 200 K or even less.

Magnetic properties of RFe4Al8 compounds studied by specific heat measurements

Specific-heat measurements have been performed on the tetragonal ThMn12-type compounds NdFe4Al8, HoFe4Al8, ErFe4Al8 and YFe4Al8 in the temperature range 1.5–200 K. There are only very small anomalies associated with the magnetic ordering of the Fe sublattice in the high-temperature part of the specific-heat curves and with the magnetic ordering of Nd and Ho in the low-temperature part. A sharp peak in the specific heat, indicative of magnetic ordering of the Er moments at 5.5 K, is observed in ErFe4Al8.

Magnetic phenomena in UNi1−xRhxAl compounds

Abstract We report on structure investigation and magnetization study of UNi 1− x Rh x Al solid solutions between an antiferromagnet UNiAl and a ferromagnet URhAl. The ZrNiAl-type hexagonal crystal structure of the parent compounds is preserved in the whole concentration range. Magnetization was measured as a function of magnetic field, temperature and external hydrostatic pressure. The observed complex evolution of magnetic phenomena with Rh substitution for Ni is discussed in terms of effects of the varying 5f-ligand hybridization. A tentative magnetic phase diagram is proposed.

Improved sample-holder design for specific-heat measurements in magnetic fields up to 17.5 T

By the use of a gold-plated silver sample holder, and a RuO2-Cernox combination thermometer, low-temperature specific-heat measurements in the temperature range from 0.35 to 90 K, and in magnetic fields up to 17.5 T, have become possible with remarkably improved accuracy. At 500 mK, the lower limit for the heat capacity that can be measured amounts to 0.02 mJ/K. The sensitivity in that case is about 0.3 μJ/K. The error margin is 1% for large heat capacities (larger than twice the sample-holder contribution) at higher temperatures, increasing to 3% for small heat capacities (half of the sample-holder contribution) around 500 mK. In high fields, for accurate measurements (error <3%) the temperature range is restricted to above 0.5 K.

A specific-heat study of RCr4Al8 compounds (R=La, Ce, Pr, Gd, Er)

Abstract Specific-heat measurements have been performed on the tetragonal ThMn 12 -type RCr 4 Al 8 compounds with R=La, Ce, Pr, Gd and Er in the temperature range 1.5–200 K. For ErCr 4 Al 8 the measurements were extended down to 0.5 K and were also carried out in an applied field of 12 T. Anomalies associated with the magnetic ordering of the R sublattice were observed in the low-temperature part of the specific-heat curves for the compounds with R=Gd and Er below about 6 and at 0.5 K, respectively. No magnetic ordering was found in PrCr 4 Al 8 and CeCr 4 Al 8 .

A specific-heat study of GdMn4Al8

Abstract Specific-heat measurements have been performed on the tetragonal ThMn 12 -type compound GdMn 4 Al 8 in the temperature range 0.3–90 K. The compound GdMn 4 Al 8 shows a Schottky type anomaly at about 2 K. From the field dependence of the specific heat, it is concluded that this anomaly is due to short-range magnetic ordering.

A specific-heat study of some RFe4Al8 compounds (R=Ce, Pr, Nd, Dy, Ho, Tm)

Abstract Specific-heat measurements have been performed on the tetragonal ThMn 12 -type RFe 4 Al 8 compounds with R=Pr, Dy and Tm in the temperature range 1.5 to 200 K. The compound PrFe 4 Al 8 gives rise to a λ-type anomaly at 11.3 K. In DyFe 4 Al 8 we found anomalies at 8.6 K and at about 30 K, while in TmFe 4 Al 8 there is an anomaly below 1.5 K. From the temperature dependence of the magnetic entropy in the presently studied compounds and from data obtained in earlier investigations, it is concluded that the overall crystal-field splitting in the RFe 4 Al 8 compounds with R=Pr, Nd, Dy, Ho, Er and Tm is less than 200 K.

Specific-heat studies of RCu4Al8 compounds (R=Er,Y)

Specific-heat measurements have been performed on the tetragonal ThMn12-type compound ErCu4Al8 and YCu4Al8 in the temperature range 1.5–200 K. A sharp peak in the specific heat, signals the antiferromagnetic transitions at TN=5.18 K. In order to separate out the effect of the Er sublattice we have also performed measurements on the YCu4Al8 compound in the same temperature range. From the temperature dependence of the magnetic contribution to the specific heat of ErCu4Al8 we obtained the temperature dependence on the magnetic entropy and discuss our results in terms of the crystal field level scheme proposed earlier from inelastic neutron scattering.

Magnetism in UPt

Bulk studies of UPt show clearly that this material orders magnetically below 28 K. In contrast to numerous previous studies we found that the low-temperature properties can be explained only by the presence of an energy gap (22-35 K) in the dispersion relation of magnons which leads to typical exponential temperature dependencies of magnetic, thermal and electrical transport properties. Another magnetic phase transition around 19 K, found by means of magnetization measurements on an as-cast sample, is most likely due to the presence of a minority phase.

Specific heat of UNiGe in high magnetic fields

Specific-heat measurements were performed on a single crystal of UNiGe in magnetic fields up to 17.5 T. This compound crystallizes in the orthorhombic TiNiSi structure and undergoes two magnetic phase transitions at 41.5 and 50 K. Besides these transitions, the specific heat also shows a Schottky contribution due to the crystal-field splitting. The effects of an applied magnetic field are compared with results from previous neutron diffraction, magnetoresistance, and magnetization measurements.