Ⅲ-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 47 (2014)

Muon spin relaxation study of spin-glass freezing in the Heusler
compound Ru1.9 Fe0.1 CrSi†
M. Hiroi,∗1,∗2 T. Hisamatsu,∗2 T. Suzuki,∗1,∗3 K. Ohishi,∗1,∗4 Y. Ishii,∗1,∗5 and I. Watanabe∗1A0 (t) = A1 exp(−λ1 t) + A2 exp(−λ2 t).

(1)

The ﬁrst and second terms represent the fast andslow relaxation components, respectively, and λ1 andλ2 are the muon spin relaxation rates for each component. The initial asymmetry A0 is A0 (0) = A1 + A2 .
The parameters in Eq. (1) were obtained from theﬁtting of the time spectra, and these temperature dependences in the ZF-µSR measurement are shown inFig. 1. As shown in the ﬁgure, a peak of the relaxation
rates was observed at ∼16 K, and this suggests the onset of spin freezing at ∼ Tg . Furthermore, LF-µSR
measurement for diﬀerent values of magnetic ﬁeld wasperformed at 0.3 K, which conﬁrmed the presence ofa static internal magnetic ﬁeld. The internal ﬁeld wasestimated to be approximately 0.1308 ± 0.005 T. Fromthese results we conclude that SG freezing occurs atTg .
On the other hand, an anomaly in the relaxation rate†∗1∗2∗3∗4∗5Condensed from the article in Phys. Rev. B 88 024409(2013)RIKEN Nishina Center
Department of Physics and Astronomy, Kagoshima University
Faculty of Engineering, Shibaura Institute of Technology
CROSS, JAEA
Department of Physics, Tokyo Medical University- 253 -

Ru1.9Fe0.1CrSi
ZF-µSR

0.5

A0A2(a)020 (b)λ2
λ10.150.1

100.0500102030T (K)40

λ2 (µs-1)

A0, A21

λ1 (µs-1)

The magnetic properties of the Heusler compounds
Ru2−x Fex CrSi have attracted interest. It has been revealed that Fe-rich compounds are ferromagnetic1) andthat the Ru-rich compound Ru2 CrSi shows an antiferromagnetic transition at TN = 14 K.2) Although
the Ru-rich compound Ru1.9 Fe0.1 CrSi was found toshow a peak in magnetic susceptibility at TN∗ ∼ 30 K,
which seemed to indicate an antiferromagnetic transition, no phase transition was found around TN∗ orat any other temperatures in the speciﬁc heat.3,4) Instead, the diﬀerence between the magnetic susceptibilities observed in a zero-ﬁeld-cooling process anda ﬁeld-cooling process increased signiﬁcantly below
Tg ∼ 15 K, which was regarded as the onset of strong
irreversibility.3) This observation suggests the formation of a spin-glass (SG) state. In order to reveal thenature of the magnetic transitions, we have performed
zero-ﬁeld (ZF) and longitudinal-ﬁeld (LF) muon-spinrelaxation (µSR) measurements for Ru1.9 Fe0.1 CrSi.
The measurements were carried out at the RIKENRAL Muon Facility using a spin-polarized single-pulse
positive surface muon beam. In these measurements
the time spectra of muon spin depolarization consistedof two components, and the asymmetry, A0 (t), can be
expressed as0Fig. 1. Temperature dependences of (a) A0 = A1 + A2
and A2 , and (b) λ1 and λ2 , for ZF-µSR. Solid lines are
guides to the eye.

of ZF-µSR, indicating a phase transition, appeared tobe absent around TN∗ , whereas with decreasing temperature a large decrease in the initial asymmetry anda gradual increase in the relaxation rates were observed starting at ∼40 K, which is slightly higher thanTN∗ . The loss of the initial asymmetry may have beencaused by a static internal ﬁeld. To investigate theorigin of the large decrease in the initial asymmetry
below ∼40 K, we performed LF-µSR measurements asa function of magnetic ﬁeld HLF between Tg and ∼ TN∗ .
The HLF dependence of A2 was analyzed, and it wasfound that at temperatures below 30 K, A2 increases
from approximately the same ﬁeld as at 0.3 K. This
analysis suggests that a static ﬁeld arises at the muonsite from temperatures higher than TN∗ ∼ 30 K and
the value of the static ﬁeld does not change much below ∼30 K. These results indicate an inhomogeneous
magnetic state. It appears that the formation of independent spin-frozen regions begins at ∼40 K. As
the temperature decreases, these static regions extend
gradually, and this results in the observed decrease in
the initial asymmetry. The correlation between staticregions becomes larger and eventually SG freezing occurs at Tg .
References
1) M. Hiroi et al.: Phys. Rev. B. 76 132401 (2007).
2) M. Hiroi et al.: J. Phys.: Conf. Series 400 032020(2012).
3) M. Hiroi et al.: Phys. Rev. B. 79 224423 (2009).
4) M. Ito et al.: Phys. Rev. B 82 024406 (2010).