A vacuum furnace has been developed, allowing muon-spin-rotation measurements between 300 and ∼1400 K. Excellent temperature homogeneity (±0.1 K over the sample volume) and temperature stability (±0.05 K) have been achieved. Incandescent halide lamps with elliptical reflectors were used for heating. The Pt-Pt10Rh thermocouples were calibrated around the Curie temperature of iron by specific heat measurements. The measured muon-spin precession frequencies in demagnetized ferromagnetic iron are directly proportional to the macroscopic spontaneous magnetization. Near the Curie temperature, an increase of the transverse relaxation of the muon-spin polarization shows that positive muons are trapped by vacancies in thermal equilibrium.
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